Natural Sugar Assisted Chemically Reinforced Highly Durable Piezo

Subscriber access provided by Kaohsiung Medical University

Applications of Polymer, Composite, and Coating Materials

Natural Sugar Assisted Chemically Reinforced Highly Durable Piezo-Organic Nanogenerator with Superior Power Density for Self-Powered Wearable Electronics Kuntal Maity, Samiran Garain, Karsten Henkel, Dieter Schmeißer, and Dipankar Mandal ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b15320 • Publication Date (Web): 20 Nov 2018 Downloaded from http://pubs.acs.org on November 21, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Natural

Sugar

Assisted

Chemically

Reinforced

Highly

Durable

Piezo-Organic

Nanogenerator with Superior Power Density for Self-Powered Wearable Electronics

Kuntal Maity,a Samiran Garain,a,b Karsten Henkel,b,c Dieter Schmeißer,b and Dipankar Mandala,d * a

Organic Nano-Piezoelectric Device Laboratory (ONPDL), Department of Physics, Jadavpur

University, Kolkata 700032, India b

Applied Physics and Sensor Technology, Brandenburg University of Technology Cottbus-

Senftenberg, K.-Wachsmann-Allee 17, 03046 Cottbus, Germany c

Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology

Cottbus-Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany d

Institute of Nano Science & Technology (INST), Mohali160062, India

* Corresponding author. E-mail addresses: [email protected], [email protected]

ABSTRACT

Natural piezoelectric material is of increasing interest particularly for applications in biocompatible, implantable, and flexible electronic devices. In this paper we introduce a cost effective, easily available natural piezoelectric material, i.e., sugar in the field of wearable piezoelectric nanogenerator (PNG) where low electrical output, biocompatibility and

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

performance durability are still critical issues. We report on a high performance piezo-organic nanogenerator (PONG) based on the hybridization of sugar encapsulated polyvinylidene fluoride (PVDF) nanofiber webs (SGNFW). We explore the crucial role of single crystal sugar having fascinating structure along with the synergistic enhancement of piezoelectricity during nanoconfinement of sugar interfaced macromolecular PVDF chains. As a consequence, the SGNFW based PONG exhibits outstanding electricity generation capability (for example ~100V under 10 kPa human finger impact and maximum power density of 33 mW/m2) in combination with sensitivity to abundantly available different mechanical sources (such as wind flow, vibration, personal electronics and acoustic vibration). Consequently, it opens up suitability in multifunctional self-powered wearable sensor designs for realistic implementation. In addition, commercially available capacitors are charged up effectively by the PONG due to its rapid energy storage capability. The high performance or the PONG not only offers the “battery free” energy generation (several portable units of LEDs and a LCD screen are powered up without using external storage) but also promises its use in wireless signal transmitting systems that widens the potential in personal health care monitoring. Furthermore, owing to the geometrical stress confinement effect, the PONG is proven to be a highly durable power generating device validated by stability test over 10 weeks. Therefore, the organic nanogenerator would be a convenient solution for portable personal electronic devices that are expected to operate in a selfpowered manner.

Keywords: Natural piezoelectric material, sugar, PVDF, organic piezoelectric nanogenerator, high performance and durability, self-powered electronics.


Page 2 of 60

Page 3 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION The recent trend of autonomous, wireless, smart and wearable electronic devices has prompted a great interest in “battery free” environment-friendly energy harvesting devices. The growing demand of alternative energy generation leaves a significant challenge to develop self-powered energy harvesting devices such as nanogenerator (NG).1─5 In this aspect piezoelectric NG (PNG) could play a significant role for scavenging energy from any type of abundant mechanical vibration available in our environment to realize a cost-effective, sustainable and portable energy source.6─9 In particular, there has been paid a considerable attention for its suitability in wearable, portable and smart electronic devices. However, key challenges still exist to enable the adoption in practical use-cases such as (i) the lack of thin wearable NG, (ii) limited power supply and energy storing capacity, (iii) biocompatibility etc. Earlier reports either rely on the integration of bulky batteries, which severely

compromise

wear

ability

or

developing

thin,

stretchable

batteries

and

supercapacitors.10─13 In addition, such systems require frequent recharging. Wang et al. first reported on a PNG in 2006 based on inorganic piezoelectric nanowire arrays.14 However, the use of inorganic material (such as BaTiO3, PZT, ZnSnO3, ZnO, ZnS, CdS and GaN) based PNGs have been limited especially in embedded in vivo self-powered wearable device realizations due to the brittleness, weight, flexibility, and biocompatibility issues.15─19 On the other hand natural piezoelectric materials such as bones, cellulose, hairs, sugar cane, collagen fibrils, peptide are increasingly interesting for self-powered biomedical systems owing to their unique crystal structure, spontaneous piezoelectricity, endless availability, costeffectiveness and adequate biocompatibility.20,21 However, many natural piezoelectric materials in this group still remain undiscovered. For example, natural sugar, a novel piezoelectric material



is always available (mainly found in the tissues of most plants and present in sugar cane and sugar beet) possess fascinating natural structure and also treated as biocompatible organic product. In particular, sugar is used in prepared foods (e.g., cookies, cakes etc.) and is also incorporated to some foods and beverages. Basically sugar is constituted of sucrose (C12H22O11), one of the most important saccharides built of fructose and glucose. The singlecrystals of sucrose belong to a monoclinic structure with P21 space group and possess only element of symmetry, i.e., binary rotation around the b-axis.22 The other crystal axes a and c are perpendicular to the b-axis where the angle between them is about 103.3o. So, the piezopotential created in the crystal due to stress application has a strong effect on the carrier transport of the materials. Thus, it is interesting to investigate the performance of natural sugar in terms of spontaneous piezoelectricity and its practical application in energy harvesting devices. However, the stability of this material is a point of agitation for their use in the self-powered technology where moisture is being considered as the main degradation source due to their intrinsic hydrophilic property.23 In such a case, encapsulation of sugar material may be an effective alternative solution for improvement of the lifecycle of the devices. Here, an interesting functionality could be added by introducing an encapsulation layer which is simultaneously useful for protecting the materials as well as for harvesting mechanical energies. Currently, flexible piezoelectric polymer materials have been increasingly used in energy harvesting devices especially in flexible electronics owing to its several advantages over inorganic materials.24 But it is still desirable to further raise the output power of these PNGs due to miniaturization of electronic devices and improvements in wireless communication technology. Thus, a hybrid organic energy harvester may be designed where the piezo-active natural component is being introduced in piezoelectric polymers. It has been found that flexible,


Page 4 of 60

Page 5 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lightweight, nontoxic PVDF is one of the best known piezoelectric polymers which has excellent potential to be used in PNGs, sensors, actuators, and biomedical applications due to its spontaneous polarization, chemical resistiveness, high thermal stability and brilliant electroactive properties, viz., piezo-, pyro-, and ferroelectricity.25,26 PVDF mainly consists of four different crystalline phases (viz., α, β, γ, and δ) in nature depending on the stereo-chemical macromolecular conformation but the main drawback is that it mainly contains stable nonelectroactive - phase (TGTG⁄ conformation). The most desired piezoelectric - phase (TTTT conformation) possess largest spontaneous polarization which is perfectly suitable for the PNG fabrication.27 In contrast, poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)), a copolymer of PVDF contains a high content of the piezoelectric -phase, but has several limitations that restrict its practical application such as a lower Curie temperature (Tc~80–110 oC, depending on the molar ratio of VDF and TrFE), less dipole (-CH2‒/-CF2‒) density due to the defect containing TrFE unit, and much higher cost than PVDF. Therefore, the nucleation of the piezoelectric -phase in PVDF is one of the prime challenges for electronic device fabrication. Over the years, several techniques (such as mechanical stretching, poling, high pressure annealing, casting from solutions and spin coating) have been used to induce the piezoelectric -phase in PVDF.28─31 However these cost-intensive and tedious processes are not so attractive due to its several disadvantages including damages of flexibility and limitation of large scale production of the films. At the same time, piezoelectric phases cannot be achieved typically unless the application of an electric field which aligns the randomly oriented molecular ‒CH2‒/‒CF2‒ dipoles along the electric field direction (called electrical poling). In addition, nanostructure based piezoelectric device designing is especially appealing due to the apparent strain confinement effect and



improved strain tolerance capability, which is usually not achievable by bulk material based designs. To overcome these issues, electrospinning, a simple, scalable and smart technique offers to induce the piezoelectric -phase in PVDF nanofiber webs (NFW) where the in-situ dipole alignment and electrical poling simultaneously take place.32,33 Thus, an electrospun PVDF NFW based PNG has become highly desirable being lightweight and comfortable to wear especially for wearable electronics devices.33 It is worth to mention that the content, dipole orientation and the degree of crystallinity are the crucial factors that result in the macroscopic piezoelectric response of the PNG. However a problem associated with the -phase orientation is that relaxation take place during the downstream electrospinning in spite of its dominance during the early stage of rapid jetting under a high electric field.34 To overcome this problem the incorporation of external assisting agents into the PVDF matrix has become one of the good alternatives.35,36 In this aspect the idea behind introduction of natural sugar into the piezoelectric PVDF could greatly assist the formation and stabilization of the oriented phase while forming oriented -CH2-/-CF2- dipoles. Hence, the enhancement of polar β-phase and the role of piezoelectric sugar in accordance with PVDF NFW are both of great importance for making composite suitable for a mechanical energy harvester. In this paper, we report on a PONG based on a novel, flexible, lightweight hybridized composite NFW, i.e., a natural piezoelectric material containing particularly sugar in the PVDF NFW. Here, sugar plays a crucial role in the performance enhancement of the PNG while it can synergistically act even as a spontaneous piezoelectric component as well as stabilizing agent. Besides, the encapsulation of the PVDF matrix prevents the degradation of the sugar from moisture and oxygen. To the best of our knowledge, no relevant study has been reported so far


Page 6 of 60

Page 7 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


where piezo-active natural sugar is explored as an assisting agent in hybridized piezo-organic NG making it superior for mechanical energy harvesting and wearable electronics. The performance durability is another crucial issue in flexible PNGs explicitly in wearable electronics owing to the use of metal foil electrodes or metal coated thin film electrodes. So, it is a great challenge to enhance the performance of the PNG particularly by keeping their flexibility and wear ability unchanged. Herein, we explore a simple, cost-effective and one-step approach to fabricate a PONG where a hybridized organic composite i.e. SGNFW act as stretchable and flexible piezoelectric component keeping soft conducting textile as top and bottom electrodes in order to overcome the drawbacks of the existing devices. Surprisingly the as-fabricated mechanically robust SGNFW based PONG offers exceptionally high power generating performance from human finger touch (Power density of 33mW/m 2 and output voltage ~ 100 V under the application of 10kPa stress) to drum beats of a toy. As a direct proof of evidence, it can drive several light emitting diodes (LEDs) instantly or power up a LCD screen in accordance with the fast energy storing capability of the PONG for different commercially available capacitors (capacitances of 1, 2.2 and 4.7 F). The high performance can be attributed to the hybridization of two piezoelectric organic materials where the single crystal sucrose encapsulated in the crystalline (β-phase) PVDF matrixes via electrostatic interactions (such as H bonding) may be considered as an overall composite of giant crystal-like structures. Therefore we hypothesize that this type of interaction and overall deformation of the composite crystal having non-centrosymmetric structure create a huge piezo-potential difference during the application of external stress between the top and bottom electrodes exhibiting an enhanced piezoelectric response.



We further demonstrate the effective electric power generation via abundantly available wind vibration and subsequently by real-life device such as “massage belt” vibration giving a meaningful energy harvesting performance. In addition, the tactile sensing performance of the PONG is also tested in front of a sound speaker driven by different musical instruments in operation such as violin, piano, guitar and kick drum. Furthermore, the PONG transmits wirelessly signals and sustains its high power under repeated mechanical impact over 10 weeks of measurements exploring its potential to be used as a sustainable energy harvester in selfpowered, multifunctional devices suitable for wearable electronics. RESULTS AND DISCUSSION Design strategy The fabrication steps of the PONG architecture are schematically illustrated in Figure 1 (a~f) . The fabrication starts with the preparation of sugar incorporated PVDF-DMF solution. Briefly, sugars were added (Figure 1a) into stock PVDF-DMF solutions (12 wt%) at an initial concentration of 0.01 g/L, homogenized by stirring for 24 h, and then sonicated by using an ultrasonic bath at 300 W for 1 h. The initial dispersion turned clear, which indicates the completion of hybridization and afterwards the solution was ready for the electrospinning process. The interaction between the sugar and PVDF chain is shown by a schematic in the right side of Figure 1a. The detailed phenomenon will be discussed below. The electrospinning of sugar containing whitish PVDF nanofiber webs (SGNFW) was started from the mentioned solution upon a grounded plate collector wrapped by an aluminum foil at an optimized distance (Figure 1b). Then the NFW was dried at 60 oC for 12 h to remove the remnant solvents. Figure 1c shows an optical image of a section of prepared SGNFW in omni-directionally stretched condition. In the next step as-prepared SGNFW (thickness of 150 m, area 12×9 cm2) was cut


Page 8 of 60

Page 9 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for the fabrication of the device (Figure 1d). Then, conducting textiles were attached as bottom and top electrodes by means of pasting adhesive tapes (Figure 1e) followed by attaching wires (Figure 1f). Finally, the as-prepared SGNFW with wired electrodes having an effective electrode area of (10.5×8) cm2 were ready for characterizations (Figure 1f). It is worthy to mention that here two types of electrospun NFWs were basically prepared for comparison, one in which sugar was introduced into the PVDF matrix and the other one, as a reference, from only neat PVDF (PNFW) followed by fabrication of two PNGs (i.e. PONG and Ref. PNG without sugar) keeping all conditions including device dimensions unchanged. Materials characterization/evaluation The encapsulation of sugar into the PVDF matrix leads to the plausible electrostatic interaction and hydrogen bonding between the hydroxyl group of sugar and PVDF dipoles. In sugar, the electropositive hydrogen is present due to the attached electronegative oxygen in the hydroxyl group and thus the surface active positive charge forms hydrogen bonds with adjacent PVDF chains at the interface to PVDF via its negative pole (i.e., fluorine atoms) as illustrated in the schematic on the right-hand side of Figure 1a. Therefore, these bonds may effect in the rearrangement of fluorine atoms up to certain extent, and consequently align more dipoles throughout the polymer chain. To provide evidence for the explanation given above, the Fourier transform infrared spectroscopy (FT-IR) spectra of sugar-PVDF composite and neat PVDF NFWs were compared in the higher wavenumber region (3700–2900 cm−1). The appearance of a broad absorption band in the SGNFW data signifies the H-bonding interaction; in contrast, there are no observable peaks in the reference data of PNFW (Figure 2a). 37,38 Notably, a huge broadening of this vibrational band occurs due to the variation of the micro–environments of the ground state of the –OH stretching vibration. In other words, the strong H-bonding interaction of



hydroxyl groups present in sucrose towards the F– ions of PVDF (i.e., O–H…F–C) leads the – CH2–/–CF2– dipoles in PVDF to be more unidirectional oriented. On the other hand, single crystal sucrose may be considered as a combination of dipole as a whole. So, there will be a bipolar interaction between the opposite poles of sucrose and the PVDF matrix, respectively. This type of electrostatic interaction may enhance the polar β-phase generation in PVDF and self-orientation as well which in turn help to reduce the threshold electric field strength required to be applied during the nanoscale device fabrication.30,34 In addition, the polar PVDF can be oriented in a much more effective way along the applied electric field during the electrospinning process which plays an effective role in directing the dipole alignment.33,39 Thus the synergistic effect of sugar induced polar configuration and subsequent electric field induced dipole alignment through electrospinning result in macromolecular chains preferentially aligned along the fiber longitudinal axis and the electric dipoles (–CH2–/–CF2–) transversely isotropic to the chains in the SGNFW.32,33,39 This interfacial interaction model is quite consistent with the FT-IR results, where the –CH2 dipoles are stretched as evident from the clear shifting of the CH2 asymmetric (νas) and symmetric (νs) stretching vibrational bands toward lower frequency for SGNFW in comparison to that of the PNFW (Figure 2b). The electrostatic interactions result in a damping of the oscillations of the –CH2– dipoles and thereby support the aforementioned shifts in the vibrational bands. In order to get a better understanding of the interfacial interaction between sugar and –CH2–/–CF2– dipoles of the PVDF matrix, X-ray photoelectron spectroscopy (XPS) was performed for SGNFW and PNFW.24,40 The high-resolution F1s core level spectra for SGNFW and PNFW exhibit a slight asymmetry when peak intensities are normalized at 688.1 eV as evident from Figure 2c.40 The asymmetry arises due to the strong interfacial interactions between sucrose and PVDF. Subsequently, this observation is strongly confirmed by the high-


Page 10 of 60

Page 11 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


resolution C1s core level spectra (Figure 2d). The C1s data of the PNFW show two peaks with binding energies of 286.7 and 291.2 eV attributed to the two main carbon species i.e. CH2 and CF2, respectively. Interestingly, a significant shift toward lower binding energies can be observed in the SGNFW, where the CH2 and CF2 peaks appeared at 285.6 and 290.2 eV respectively (illustrated by ΔBECF2) in the SGNFW data. These changes suggest a notable variation in the electronic environment of the CH2 and CF2 species of PVDF due to electrostatic interactions between the sucrose molecules and PVDF moieties in the SGNFW.27 Furthermore, in the C1s data, a substantial difference in the peak intensity (area) between the spectra of SGNFW and PNFW is monitored, particularly if the data are normalized to the CH 2 peak. The SGNFW spectrum clearly exhibits a reduction of the CF2 peak area particularly when the CH2 peak intensities are normalized, confirming further the aforementioned interfacial interactions.40 In addition, the O1s spectrum of the SGNFW (Figure 2e) confirms the presence of oxygen in the sucrose molecule, whereas no related oxygen signal could be sensed for the PNFW. The deconvolution of the O1s spectrum clearly indicates two main components, where the peak at 532.8 eV is assigned to C–O, and the one at 533.7 eV to O–C–O. This observation is consistent with the strong OH stretching vibrational band in the FT-IR spectra (Figure 2a) strongly confirming the presence of sugar in the PVDF molecular chain. Subsequently, elemental quantification was performed using the energy-dispersive X-ray (EDX) spectrum of the SGNFW which shows O along with C and F (Figure 2f). The appearance of F and carbon C signal is mainly arising from the PVDF matrix while O contributions originate from the presence of sugar in the SGNFW. It also suggests that the solvent was evaporated completely because no nitrogen signals were detected. This is further evidenced by the elemental mapping images of oxygen (O) along with carbon (C) and fluorine (F) (Figures 2 g,h,i).



Page 12 of 60

Overall, the afore-described interfacial interaction promotes the -phase formation of PVDF in the SGNFW. Here, it is worthy to mention that a very small amount of sugar can hinder the phase nucleation and increase the-phase content in the PVDF matrix as evident from the comparison of the FT-IR spectra of SGNFW and PNFW (Figure 2j). The vibrational bands at 614, 763, and 975 cm─1 in PNFW are mainly attributed to the non-polar -phase. In contrast, these the bands are diminished in the spectra of SGNFW while two other arrow-marked new peaks at 1053 and 995 cm─1 are appearing, indicating the interaction between sugar and the PVDF matrix. These bands are assigned to the C–O stretching modes ν(C-O) of a sucrose molecule which in turn confirm the presence of sugar in the PVDF composite. 41 At the same time the piezoelectric β-phase can be well-identified from the vibrational bands at 1276 and 840 cm─1, respectively (Figure 2j). Due to the electrospinning process, also in the PNFW spectrum the β-phase is clearly present; however the β-phase related peaks are more intense in the SGNFW data evidencing the higher yield of the polar β-phase24. The relative proportions of the electroactive phases (𝐹𝐸𝐴 ) within the NFWs are quantified from Beer-Lambert law using the following equation: 𝐹𝐸𝐴 =

𝐴840 𝐾 ( 840 )𝐴763 +𝐴840

× 100%

(1)

𝐾763

where 𝐴840 and 𝐴763 are the absorbance intensities at 840 and 763 cm-1 respectively, and K840 (7.7 × 104 cm2 mol−1) and K763 (6.1 × 104 cm2 mol−1) are the absorption coefficients at the respective wavenumbers.30 An FEA value of less than 90% is achieved in PNFW whereas this value is more than 95% for SGNFW attributing the formation of the enhanced piezoelectric phase due to the hybridization of sugar and PVDF. Here, the role of sugar is very crucial; it not only induced but also stabilizes the electroactive phases during rapid crystallization of SGNFW


Page 13 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


during the electrospinning process. In addition, we have also recorded the FT-IR spectra of the SGNFW under increasing relative humidity to observe its effect upon SGNFW (Supporting information, Figure S1a). However the respective results clearly exhibit the presence of the same content of the polar -phase and no significant change is observed although the relative humidity is changed. As a result, the generation of the polar crystalline β-phase is irreversible in SGNFW and no back-relaxation to the α-phase by any thermal treatment occurs. This statement is further supported by the observation from in-situ temperature dependent FT-IR spectroscopy (Figure 2k).42 The thermal behavior of the crystalline polymorph (- phase) is achieved when the absorbance intensity of the -phase (1276) is plotted vs. temperature (Figure 2k). Though, the melting point (tm) of the -phase at 158 oC is confirmed from this plot (Figure 2k), the β-phase representing vibrational band at 1276 cm-1 still exists even at 180 oC (inset of Figure 2k). Therefore, it is expected that the device could operate up to a wide temperature region (27 oC to 158 oC), as polar phase is mainly responsible for the piezoelectric outcome.42 Thus the introduction of sugar in PVDF acts as an assisting agent for the crystalline β-phase in SGNFW, the all-trans conformation of PVDF is thermodynamically stabilized with interfacial interaction phenomena. In addition, the crystallization behavior of the NFWs was investigated to identify their crystalline phases and to quantify the degree of crystallinity by curve-deconvoluted X-Ray diffraction (XRD) patterns (Figures 2 l,m). In the XRD spectra, the curve-deconvoluted sharp peak at 20.8° [(110)/(200)] indicates that the β-phase is predominant in SGNFW as well as in PNFW where this peak is, however, a bit less intense. Furthermore, it is obvious that PNFW carries a higher fraction of the non-polar -phase as evident from the more pronounced diffraction peaks of the -phase at 2 = 19.6° (110) and 18.3° (020).24,27,30 So, it implies that the



Page 14 of 60

content of the -phase decreases and that of polar -phase increases in SGNFW in contrast to the neat one (PNFW). This result is in good agreement with the FT-IR spectra supporting our observations given before. The total degree of crystallinity could be deduced from the following equation, 𝜒𝑐 𝑡 = ∑ 𝐴

∑ 𝐴𝑐𝑟

𝑐𝑟

+ ∑ 𝐴𝑎𝑚𝑟

× 100%

(2)

where ΣAcr and ΣAamr are the summation of the integral areas of the crystalline peaks and the amorphous halo respectively.27,30 Therefore the degrees of β-crystallinity (𝜒𝑐 𝛽 ) and crystallinity (𝜒𝑐 𝛼 ) are calculated by the following equations: 𝜒𝑐 𝛽 = 𝜒𝑐 𝑡 × ∑ 𝜒𝑐 𝛼 = 𝜒𝑐 𝑡 × ∑

∑ 𝐴𝛽 𝐴𝛽 + ∑ 𝐴𝛼 ∑ 𝐴𝛼

𝐴𝛽 + ∑ 𝐴𝛼

×100%

×100%

(3) (4)

The corresponding values were calculated and are labeled in Figure 2 l,m. Obviously, the interaction of sugar in the PVDF matrix leads to the yield of the piezoelectric -phase in SGNFW (𝜒𝑐𝛽 ≈ 56%) in comparison to PNFW (𝜒𝑐𝛽 ≈ 43%). Thus, the total crystallinity (𝜒𝑐𝑡 ) of the SGNFW becomes higher (≈ 59%) than that of PNFW (≈ 53%). So, the hybridization of single crystal sugar and the PVDF matrix affects the resultant properties significantly because of the overall improvement of crystallinity.30,43 Basically, the NFW was the prime component of the NG owing to their excellent flexibility. So, it is necessary to study the surface morphology and nanostructure. The field emission scanning electron microscope (FE-SEM) images reveal that the NFWs were randomly oriented having rough surfaces and no bead defects were observed for PNFW and SGNFW (Figures 3a and 3b). Notably, the incorporated sugar is well dispersed in

the PVDF matrix making

considerably reduced diameter for SGNFW (average fiber diameter ~ 125 nm) compared to that


Page 15 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of PNFW (average fiber diameter ~250 nm) which is also evident from the corresponding histogram profiles (insets of Figures 3 a,b). It should be mentioned that a fixed humidity (2030%) was maintained during the electrospinning process within the SGNFW preparation routine because the increase of humidity results in the appearance of bead defects. Beyond a certain level of humidity the web is full of beads which are not useful for device fabrication (Supporting Information, Figures S1b and S1c). The two dimensional (2D) fast Fourier transform (FFT) of the FE-SEM image of SGNFW yields the quantitative analysis on the degree of alignment. A highly symmetric, circular distribution of the pixel intensity confirms the randomly oriented nanofiber webs along with a featureless behavior of the radial pixel intensity versus polar angle (Figure 3c and inset). In other words, a symmetric distribution of the pixel intensity implies that the particular frequency at which pixel intensities occur in the respective 2D FFT image (inset of Figure 3c) is almost identical in any direction and this observation is also confirmed from no observable peaks when plotting the sum of the pixel intensity as a function of the polar angle in the region of 0–180° (Figure 3). This analysis further evidences the randomly networked structure of the SGNFW. However, the molecular orientation of the SGNFW neither depends on randomized nanofiber distribution nor on nanofiber diameter rather upon the synergistic effect of applied high electric field and mechanical stretching during electrospinning process.33 This is already confirmed by our FT-IR data reported above. In addition, for the decreasing of the fiber diameter, the resultant crystallinity, and overall piezoelectric performance has been greatly improved.24,34,43 The present state of the art depending on nanofiber orientation and device performance is shown in a comparison table (Supporting Information, Table S1).



Page 16 of 60

The transmission electron microscopy (TEM) image (Figure 3d) and high resolution TEM image (right upper inset of Figure 3d) of the SGNFW reveal that sugar is encapsulated within the PVDF which implies the nanoscale interfacing of sugar within the macromolecular chain of PVDF. The corresponding selected area electron diffraction (SAED) pattern (left lower inset of Figure 3d) of the SGNFW unveils the highly crystalline structure of sugar and respective lattice planes are indexed.44 The clear diffraction spots from single crystal sugar embedded within the diffraction rings of PVDF are well identified in the SAED pattern which further confirms the presence of sugar in the PVDF matrix. In addition, the XRD peaks of SGNFW appeared at 31.9°, 33.3°, 36.0°, 37.2°, 38.3°, 46.7°, 50.6° and 56.6° corresponds to the diffraction from lattice planes of sugar as evident from the respective XRD peaks of sugar (Supporting Information, Figure S2).44 This result further confirms the presence of sugar within the PVDF NFW. Subsequently, the mechanical properties of the SGNFW and PNFW were investigated under extreme stress to get an idea of its applicability in environmentally harsh conditions. In general, the output response of a piezoelectric material can be presented by the constitutive piezoelectric strain-charge equation, 𝐷𝑖 = 𝑑𝑖𝑗 𝜎𝑗 = 𝑑𝑖𝑗 𝑌𝑘𝑗 𝜀𝑘

(5)

where 𝐷𝑖 is the electric charge separation, 𝑑𝑖𝑗 is the piezoelectric coefficient, 𝜎𝑗 is the applied stress, 𝑌𝑘𝑗 is the Young's modulus and 𝜀𝑘 is the applied strain. It is evident from the equation that changes of 𝑑𝑖𝑗 and 𝑌𝑘𝑗 both collectively contribute to the piezoelectric output performance and affect the energy harvesting efficiency significantly.43 Thus, the mechanical aspects of piezoelectric materials are equally important along with the contribution of the piezoelectric coefficient to enhance the overall piezoelectric response. Figure 3e presents the corresponding stress-strain curves which clearly display an enhanced stretch-ability of up to 60% for the


Page 17 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SGNFW compared to 21% for the PNFW accompanied by a significantly higher Young’s Modulus (Y) of 40 MPa for the SGNFW than of 9 MPa for the PNFW. The improvement of mechanical properties in SGNFW may be ascribed to the stress concentration caused by the sucrose molecule within the PVDF matrix resulting in an enhanced degree of crystallinity. It is noteworthy that polymer chains become less mobile in accordance with the raising of the crystalline part in the composite and hence it is more difficult to stretch the material, thereby assisting improved mechanical responses. Thus the higher toughness of the SGNFW than that of the PNFW upon the application of tensile stress makes it more promising for practical applications. In addition, the flexible nature of the SGNFW is also demonstrated in the optical images by rolling, twisting and folding (Fig. 3 f-h). Therefore, the good stretch-ability, enhanced elasticity and higher toughness of the SGNFW open its potential for wearable PONG fabrication. Next, we discuss the macroscopic polarization responses of the NFWs to support our previous observations. A superior response is observed for the SGNFW (Figure 4a,b) in comparison with the PNFW (Supporting Information, Figure S3). The SGNFW possesses a high remnant polarization (Pr) of 0.13 μC/cm2 with negligible loss of spontaneous polarization (Ps) at E = 0 (i.e., Pr/Ps ~ 0.7) whereas the PNFW exhibits Pr/Ps ~ 0.3 as evident from Figure 4a and Supporting Information, Figure S3a. The corresponding current density vs. electric field (J-E) loops of the PNFW and SGNFW are shown in the Supporting Information, Figure S3 (b and c). The average coercive field (Ec) of the SGNFW above which the dipoles are switched back and forth is found to be 10 kV/cm. The switching current density at the E c is 0.2 μA/cm2. The symmetrical current curves for both increasing and decreasing electric field mainly arise due to the current induced by the dipole reversal where leakage and capacitive charging currents are comparatively negligible.45 In addition, the electric field induced strain amplitude (S) response



Page 18 of 60

corresponding to the P-E loop due to the converse piezoelectric effect is shown by butterfly shaped hysteresis loop (S vs. E) (Figure 4b). This observation further confirms that the polarization response arises only due to the dipole reversal process and is not based on conduction mechanism. The piezoelectric charge coefficient (d33) can be obtained as, 𝑑33 = −

𝑃𝑟 𝑌

= −33 𝑝𝐶/𝑁

(6)

where Y is the Young’s modulus determined above (refer to Figure 3e). Hence, the SGNFW possess a negative longitudinal piezoelectric coefficient and contracts under the electric field. In addition, the longitudinal electrostrictive coefficient (Q) can be evaluated as S= QP2 from the SE loop. The slope of S vs. P2 yields Q ~ 0.78 m4 C−2 (Supporting Information, Figure S3d) which is a higher value than that of many inorganic and organic piezoelectric materials. Thus the P-E and S-E hysteresis loops of the SGNFW suggest the preferential alignment of electric dipoles along the direction of the applied electric field within the crystalline regions. This polarization response may be attributed to the combined effect of piezoelectric β-phase acting as nanodimensional dipoles (nano-dipole) and piezo-electret properties of micro-voids in the SGNFW behaving as micro-dipoles under the applied electric field.39,46 It is well known that the aligned dipoles in the nanofiber webs can create boundaries carrying the polarity charges at the nanofiber surfaces. Subsequently, a large amount of space charges are localized to form charged voids and electret dipoles between these polarized nanofibers resulting in inhomogeneous surface charge distributions.39 Generally, charges are artificially injected into macroscopic voids of porous polymers which subsequently assist to create the oriented “quasi-dipoles” known as electrets.45,46 In this case, a large amount of charges are primarily being localized caused by the fibrous structure of the SGNFW. In addition, the sugar incorporation influences the charge mobilization in the SGNFW, and thereby assists the hetero-polarization inside the NFW.39 Therefore, a charge


Page 19 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


separation has already occurred during nanofabrication of the SGNFW. Thus this co-operative phenomenon from piezoelectric β-phase and piezo-electret may result in a phase-lag of loop under the sweeping of electric field identified by a not perfectly closed hysteresis loop in Figure 4a.46,47 Figures 4c and 4d exhibit the dielectric permittivity (εr) and dielectric loss (tan δ) of the SGNFW and the PNFW as a function of frequency in the range of 1 kHz to 1 MHz at room temperature. The sugar incorporation assists the enhanced dielectric constant (εr ~ 12 at 1 kHz) of the SGNFW in comparison to the PNFW (εr ~ 6.2 at 1 kHz) whereas the dielectric loss is higher at low frequencies for the SGNFW (e.g., tan δ ~ 0.04 at 1 kHz) compared to PNFW (e.g., tan δ ~0.004 at 1 kHz).This is a well-known phenomenon that the dielectric constant of a material is related to the degree of polarizations which mainly contributes to the enhancement of the dielectric constant at lower frequency, whereas at higher frequency the molecules can’t follow the alternation of the electric field. On the other hand, the strong hydrogen bonding between hydroxyl group of sucrose and the PVDF matrix (e.g., O–H and C–F) (scheme of Figure 1a) results in the highest dipole moment because dipole–dipole correlation is more prominent than its dipolar aprotic counterpart. So it is conclusive that this fact mainly contributes to the enhanced value of εr of the SGNFW. Piezoelectric energy harvesting performance In order to check the energy harvesting performance of a PONG based on the SGNFW, the PONG was impacted by human finger (covered in a polyethylene (PE) glove) applying different compressive normal stress (a) periodically through pressing and releasing. The corresponding test bench setup is shown in Supporting Information, Note S1 and Figure S4. The harvested open-circuit voltage (Voc) of the PONG increases remarkably from 35V to 100V when a raises from 1 kPa to 10 kPa (Figure 5a). In contrast, the Ref. PNG exhibits smaller Voc of 12 V to 43 V



Page 20 of 60

under the application of the same a as shown in Figure 5b. The PONG easily converts the mechanical human finger touch into electricity under press-release motions (inset of Figure 5a). The average mechanical sensitivity (Sm) of the PONG can be calculated from the following equation: 𝑆𝑚 =

∆𝑉𝑂𝐶

(7)

∆𝜎𝑎

It is found to be 7.2 V(kPa)─1 in the pressure range of 1–10 kPa from the slope of the curve of Figure 5a (upper inset) which is superior compared to previously reported PNG.24,30,48,49 It implies that the hybridization of two piezoelectric materials greatly influences the output piezoelectric performance of NG devices. The superior energy harvesting performance of the PONG is attributed to the higher piezoelectric charge coefficient (d33) and as a result it exhibits superior piezoelectric figure of merit (FoM ≈ d33. g33 ≈ 10.23 × 10-12 Pa-1) than the Ref. PNG (FoM ≈ 7 × 10-12 Pa-1) where the g3j can be calculated as, 𝑔3𝑗 =

𝑑3𝑗 𝜀0 𝜀𝑟

. Here the subscript ‘j’

denotes the direction 1 (X-axis) or 3 (Z-axis) of induced strain of a three-dimensional coordinate system and 𝜀0 is the permittivity of free space. The corresponding switching polarity test was performed by reversing the electrode connections to verify that the output voltage is governed by the piezoelectric properties of the PONG (Supporting Information, Figure S5).48,50 In this case, the same amplitude of output voltage with opposite polarization cancels out any additional contribution of artefacts or friction. In addition, it also confirms that the piezoelectric output voltage is coming only from the SGNFW. So, this is an indirect proof of dipole alignment which is in good agreement with the FT-IR spectra (Figure 2f).32,33 Additionally, for ruling out electrostatic contributions to the output electrical response of the PONG a control device made only with a non-piezoelectric material polydimethylsiloxane (PDMS) (without NFWs) keeping device dimension (area 12×9, thickness ~ 150 m) and other conditions unchanged was


Page 21 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


fabricated and tested, where indeed no considerable output voltage is observed (Supporting Information, Figure S6).48 Furthermore, the high sensitivity of the PONG is also demonstrated by attaching the device upon a drum of a toy and the respective output voltage response was recorded during the repeated drum beats (Figure 5c). It is remarkable that a significant output voltage of ~ 5 V under the gentle imparting of drum beats of a toy is detected opening the potential use of the PONG in real life applications. Subsequently, the current measurements of the PONG showed a well–behaved periodic alternation of positive and negative peaks of short-circuit current (Isc) of about 6.2 A during human finger imparting (10 kPa) (Figure 5d). The magnitude of generated charge (Q) under the applied force, F ~ 84 N, is calculated by the integration of a current pulse, i.e., using the following equation: 𝑄 = ∫ 𝐼𝑆𝑐 𝑑𝑡.

(8)

It evaluates Q ~ 3192 pC (Supporting Information, Figure S7). Thus, the estimated magnitude of piezoelectric coefficient is given by, 𝑑33 =

𝑄 𝐹

(9)

which leads to the value of 38 pC/N.51 This result is in close agreement with the value calculated by the P-E loops (d33 ~ 33 pC/N) using Equation 4. So the axial strain ε achieved in the PONG by human finger application is 2.5 × 10-4, calculated from Equation 5𝑢𝑠𝑖𝑛𝑔 Y~ 40 MPa. The corresponding strain rate ε̇ is developed by 0.5 % s-1 assuming that the PONG undertook compressive strain for a repetitive mechanical stress, using the relation 𝜀̇ = 4𝑓𝜀 × 100 % 𝑠 −1 , where the average frequency of the axial stress is 𝑓~ 5 Hz.46 Furthermore, the bridge rectified instantaneous output voltage (VL) and current (IL) of the PONG are measured as a function of an



Page 22 of 60

externally connected load resistance (RL).24,34 It has been observed that VL across the resistance gradually increases with the change of RL accordingly and saturated at infinitely high resistance (~ 30 M) comparable to the open circuit voltage (Figure 5e). The calculated IL is gradually decreased upon increasing the RL (Figure 5e). The PONG is able to deliver a maximal instantaneous power density of 33 mW/m2 at the RL of 15 MΩ converting mechanical energy to electric energy taking into account the following equation: 𝑃=

𝑉𝐿2 𝑅𝐿

(10)

The variation of P with RL is shown in Figure 5f. Thus, with this superior power density the PONG is able to drive several blue or green LEDs separately without the need of any external batteries (upper and lower insets of Figure 5f). The corresponding LEDs driving circuit and typical current–voltage (I–V) characteristic curve of the blue LEDs powered by the PONG are shown in Supporting Information, Figure S8. The latter one clearly indicates the threshold voltage and current requirement to light up the LEDs. Therefore, the power delivered by the PONG is well above the threshold requirement.24 Furthermore, superior instantaneous piezoelectric energy conversion efficiency (ηpiezo) of the PONG up to 64% is also achieved (see Supporting Information, Note S2 and Figure S9, for details). Therefore, the PONG acts as an excellent power source under mechanical impact. The internal resistance (Ri) of the PONG is evaluated as 13.5 MΩ using linear circuit theory (see Supporting Information, Note S3 and Figure S10, for details). The output power is found to be maximal approximately at R i≈RL due to impedance matching between internal and external systems. To the best of our knowledge, the output performance of the PONG is much higher than that achieved with previous reported PNGs made with PVDF NFs as shown in Table 1. Discussion of the improved piezoelectric performance of the hybrid PONG


Page 23 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The superior performance of the PONG could be attributed to the hybridization of sugar and PVDF. In sugar, glucose and fructose are connected via an oxygen atom (Figure 6a) where the cell dimensions are as follows, a = 10.89 Å, b = 8.69 Å, c= 7.77 Å and  = 103o. Each unit cell consists of two sucrose molecules and most of the dipoles share approximately the same orientation via hydrogen–oxygen bonds between the molecules. The typical shape of sucrose single-crystals and the axes orientation are shown in the schematic of Figure 6b where the main planes are indicated by arrow marks. In the crystalline structure of sucrose, the molecule is folded and two additional hydrogen bonds to oxygen atoms are built within the molecule. The binding between the molecules in the crystal structure is also formed by hydrogen bonds to oxygen atoms.22 Thus, every sucrose molecule is interconnected with the adjacent molecules via several weak bonds in this way. It is noteworthy that these bonds between them are not stiff as the molecules itself are heavy. So, any type of stress application easily deforms the crystalline lattice of sucrose and therefore the stress-induced net charges can result in the variation of carrier transport in the single crystal of sugar. The plausible explanation behind the enhanced piezo-response of the hybrid SGNFW composite is based on a combined effect of two piezoelectric materials with increased overall polarization where the single sugar crystal is attached to PVDF via electrostatic interaction/H-bonding. In other words, PVDF chains occupy the interstitial positions in sugar (and vice versa) where the -CF2 dipoles interact with H and the CH2 dipoles with O. As a synergistic effect of this kind of interaction and intercalation, the improvement of electroactive crystalline phases in PVDF along with the generation of piezoactive sugar is favored. Thus, the deformation of the overall giant crystal structures in sugarPVDF composite causes the huge enhancement in piezoelectric performance. Interestingly when



the PONG is subjected to vertical compressive pressing/releasing (Figure 6c), the crystal structure of the SGNFW is deformed creating a positive potential at the bottom electrode and a negative potential at the top electrode surface of the PONG. Thus, a huge potential difference between the top and bottom electrodes causes the electrons in the external circuit to flow back and forth leading to the alteration of the piezoelectric charge polarization of Voc~ 100 V and Isc~ 6.2 μA with very fast response time (5 ms) (Supporting Information, Figure S11). In order to get quantitative explanation on this piezoelectric mechanism exclusively, we further made theoretical simulations where compressive forces are applied in the direction normal to the plane constructed by the networked structure of the SGNFW. The simulation was conducted by the Finite Element Method (FEM) using COMSOL multiphysics software to describe how the electromechanical interaction among nanofibers at micro-scale affects the resulting longitudinal polarization under compressive stress.49,3 It is mainly presented by six SGNFWs constructing a network-like structure and the piezo-voltage distribution (colored zaxial scale bar) between two electrodes inside the deformed SGNFW under stress of σa ~ 10 kPa (Figure 6d). A 3-dimensional geometry is required for the simulation in COMSOL where a single nanofiber is considered as a cylinder with a diameter of 125 nm. In this study, we consider isotropic bulk material properties of the SGNFW. The used material properties within the FEM simulation are given in the Table S2. The model is meshed with ‘physics controlled mesh’ and element size ‘fine’ is used. The meshed model is shown in Figure S12. The detailed simulation process is described in Supporting Information, Note S4, Table S2 and Figure S12.49,3 The experimentally measured maximum piezo-potential (~100V) was slightly lower than the simulated result of 118 V. This variation occurs probably due to the voltage drop from internal leakage paths and charge losses in the electrode-insulator junctions.60 The corresponding surface


Page 24 of 60

Page 25 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


charge density and displacements distributions due to the applied stress are determined consecutively and are shown in Figures 6e and 6f respectively. In an obvious manner, charge density differences between the top and bottom surfaces of the SGNFW exhibit the potential differences as evident from the color bar whereas the deformations are shown in the region of applied stress resulting in attenuated displacements from its original position among the NFWs. The interaction behavior between structural and electrical properties of the PONG can be classically described by the following equations: 𝑇 = 𝑐𝐸 𝑆 + 𝑒 𝑇 𝐸

(11)

𝐷 = 𝑒𝑆 + 𝜀0 𝜀𝑟𝑆 𝐸

(12)

where 𝑇 and 𝑐𝐸 are the stress tensor and the elasticity tensor respectively, (𝑒)𝑖𝑗𝑘 is the piezoelectric tensor, S is the mechanical strain, 𝜀𝑟𝑆 is the dielectric tensor, 𝜀0 is the permittivity in vacuum and 𝐸 is the electric field.61 As the piezoelectric SGNFW is anisotropic in nature, the piezoelectric polarization field (P) under a small uniform mechanical strain is given by: 𝑃𝑖 = (𝑒)𝑖𝑗𝑘 (𝑆)𝑗𝑘

(13)

Then the calculated displacement current from the media polarization is 𝐽𝐷𝑖 =

𝜕𝑃𝑖 𝜕𝑡

𝜕𝑆

= (𝑒)𝑖𝑗𝑘 ( 𝜕𝑡 )

𝑗𝑘

(14)

which implies that the changing rate of the applied strain is directly proportional to the output current density of the PONG. Thus, the measured output piezoelectric performance of the PONG upon different applied strain strongly agrees with the above theory. Energy harvesting performance from abundant sources



Now we demonstrate the piezoelectric power generation from normally wasted mechanical energy surrounding systems as our environment is full of abundant vibration (for example, wind, acoustics, human movement etc.). As a result we can convert it into usable energy for operating electronic devices. Besides, the ability to differentiate multiple frequencies of vibrations is also critical for an efficient device performance. So at first, we started with wind vibration, the corresponding setup is sown in the scheme (Figure 7a). For exclusive optimization, we varied different depending parameters such as distance from wind-blower to PONG (60, 120, 176, 234 and 300 cm), speed of the wind-blower (1, 4, 8, 12, 16 and 20 ms-1) and effective area of the PONG (45, 63, 81 and 108 cm2). The respective real-time voltage signal responses from the PONG are shown in the Figures 7b-d and the insets show the voltages as a function of corresponding parameters i.e. distance velocity and effective area respectively. It was expected that the variation of the distance affects the wind vibration-to-electric conversion. We observed decreasing output voltage response and sensitivity with increasing distance (from 60 to 300 cm) between the wind-blower and the PONG (Figure 7b). The speed of the wind blower also affected the voltage output response of the PONG. When the velocity increased from 1 to 12 ms -1, the output voltage increased from 0.5 to 3.5 V. Further increasing the speed of the blower (16 to 20 ms-1) led to decrease in both sensitivity and voltage (Figure 7c). Also, the effective area of the PONG was found to be an important parameter for the output response when the PONG is placed in front of the wind vibration keeping distance and wind blowing speed fixed. The output voltage of the PONG showed a moderate increase with the effective area increasing (45 to 108 cm 2) (Figure 7d). Apparently, it is evident that the voltage output profile and sensitivity of the PONG is greatly affected by the wind vibration influenced by different experimental parameters. This can be explained by the effect of the wind-vibration upon the main piezo-active component of


Page 26 of 60

Page 27 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the PONG, i.e., SGNFW. It is well-known that polymeric NFWs are flexible and thereby easy to vibrate under external mechanical waves. It is worthy to mention that the absorbed vibration in the NFW caused by external source is mainly localized and in this case the nanofiber deformations differ to those resulted from compression or bending of the NFW as the mechanical deformation in the latter case spans the whole fibrous networked structure. Thus, the decreasing output response of the SGNFW based sensor device with increasing distance of the wind-blower could be attributed to the fact that the weak vibrational waves are damped in the surrounding medium. In contrast, the vibration-effect becomes higher with increased effective active area of the PONG exposed in-front of the wind-blower. However, the effect of the speed of the windblower is different as the output voltage response first increases to a certain point of external stimulation (12 ms-1) and beyond it decreases. Here different effects such as turbulences in the stimulating wind or the disability of the active dipoles to follow the exciting vibrational frequency might be responsible. Then, we proceed with a real-life tool demonstration by a massage belt attached to human body parts and the PONG is fixed with the belt (inset of Fig. 7e). The open-circuit voltage response is shown in the Figure 7e during message belt vibration “OFF” and “ON” conditions, which implies the sensitivity and promising output performance of the PONG. Furthermore, the acoustoelectric conversion sensitivity of the PONG is demonstrated (Figure 7f) by different musical instruments (violin, piano, guitar and kick drum) in operation where the PONG device is placed in front a sound speaker connected to the instruments under the sound pressure label (SPL) of 85 dB at a frequency of 130 Hz (scheme is shown in the inset of Figure 7f). The distinguishable output voltages patterns show the potential of the PONG as an acoustic sensor as



Page 28 of 60

well as energy harvester. Thus the energy harvesting performance of the PONG from different abundant sources makes it a stand-alone device in self-powered application system. Energy storing performance, application in wireless system and stability test Besides instantaneous energy generation, some applications effectively require fast charging or reaching a higher voltage at a certain time. In view of this practical requirement, we investigate the unique charging ability of the PONG by choosing capacitors as an energy storage system. Thus, three capacitors (e.g., 1, 2.2, and 4.7 F) are connected to the PONG via full wave bridge rectifying circuit and charged them up via repeated applied stress (Supporting Information, Figure S13). Figure 8a shows that the generated voltage of the PONG is rectified to charge the capacitors exponentially to reach the steady state. All the three capacitors are charged under identical conditions, and the stored voltages increase exponentially and reached steady states in a very short time. The fast charging ensures the rapid energy supply ability of the PONG. The average power stored inside the capacitors can be calculated from the following equation: 𝑃=

𝐶𝑉𝑠 2 2𝑡

(15)

where C is the capacitance of the capacitor, Vs is the saturation voltage and t is the time taken for the capacitor to reach the steady state (Figure 8b). Thus the outstanding capacitor charging performances greatly promise to power up tiny portable electronics. Subsequently, for potential application of our organic nanogenerator, we used the PONG to power up a LCD screen from “OFF” state to “ON” state from the stored energy in the 1F capacitor under the repeated applied stress of about 10 kPa via the bridge rectifying circuit (mentioned in experimental section) without using any external power sources (Figure 8b upper inset). Moreover, the PONG is also demonstrated to be useable as power source for the wireless signal transfer of the pressure impact in terms of the applied voltage. The setup for this application can be arranged by


Page 29 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


integrating a transmitter (here an infrared LED is used) which actually transmits the signal generated by the PONG under pressure impact (~2 kPa) and a receiver (here a photodiode is used) captures the transmitted signal. Finally we measure the output signal by a digital oscilloscope (the circuit diagram is shown in Figure 8c). In particular, the PONG generated signal acted as a source that is possible to be detected wirelessly via photodetectors (Figure 8d). Thus, the PONG is expected to be suitable for wireless signal transfer system in short scale, which is particularly useful in personal health care monitoring. Finally, the robustness of the PONG device has been tested by the stability of the electrical output to demonstrate its advantage and reliability. Average stable amplitude of the output voltage is observed during the continuous operation of 24,000 cycles (impacting the device at 3 Hz for ~ 8000 s by a stepping motor under the pressure of 0.9 kPa) (Figure 8e). In addition, the long term period (~ 10 weeks) mechanical durability test shows less than ±6% of electrical output fluctuation without remarkable degradation which strongly affirms that the environmental moisture does not affect any more the performance of the PONG (Figure 8f). Meanwhile, the nanofibers morphology of the SGNFW surface exhibits no significant distortion or serious damage after continuous impact for long term period (10 weeks), as shown in the insets of Figure 8f. This validates the fatigue test of the PONG. Furthermore, we study the effect of different humidity conditions upon the piezoelectric performance of the PONG keeping other conditions unchanged (Supporting Information, Figure S14). The corresponding results evidence no significant changes in the piezoelectric responses from the PONG under finger imparting (a ~ 10 kPa) in spite of increasing relative humidity. Thus, the outstanding robustness of the PONG enables long-term stability under harsh environment, which is considered to be a significant factor of organic nanogenerators in mechanical energy harvesting applications.



The superior performance and robustness of the PONG are primarily attributed to its all-fiber structure, which enables the enhanced collection of charges by the conducting fabric electrodes and thereby improved energy conversion efficiency of the device. CONCLUSIONS In summary, we have demonstrated a fully packaged high performance PONG based on natural sugar introduced PVDF NFW that can be used for enhanced electrical energy generation with superior power density for self-powered multifunctional wearable electronics. Furthermore, the energy generation capability and sensitivity from abundant mechanical sources (such as wind, personal electronics and acoustic vibration) are exclusively demonstrated (optimizing different depending parameters) besides its rapid energy storage capability (commercial available capacitors are charged up). The high performance is sufficient enough to power up several LEDs and a LCD screen without using any external battery besides its suitability in wireless signal transmitting system. Finally, the mechanical durability and robustness of the PONG has been tested by observing stable amplitude of the electrical output during continuous mechanical impact for long term period (~10 weeks). Therefore, this organic nanogenerator provides an effective prospect for harvesting energy in self-powered wearable electronics. EXPERIMENTAL SECTION Materials. PVDF pellets (M̅w ≈ 275 000, Sigma-Aldrich, USA), N,N-dimethylformamide (DMF), acetone (Merck Chemical, India), Sugar (Commercially available). Preparation of nanofiberwebs. The schematic of the preparation of NFW is shown in Figure 1 a,b. At first the PVDF solution was prepared by dissolving PVDF pellets in DMF/acetone (6:4) at a polymer/solvent concentration of 12% w/v under continuous stirring until a clear solution was obtained. Then sugar was incorporated into the stock PVDF solution. The NFW was


Page 30 of 60

Page 31 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


prepared by using a typical electrospinning setup.24 Electrospinning was performed by placing 10 ml of solution within 15 ml commercially available plastic syringe (DISPOVAN) tipped with a 22 G stainless steel needle fed by using a syringe pump with a constant rate of 0.6 mlh -1. A positive high voltage (11 kV) was applied between the metal needle and the Al foil wrapped collector, where the needle-to-collector distance of 12 cm was adjusted. A relative humidity of 20−30% is maintained throughout the electrospinning process at room temperature. For the investigation of the influence of the humidity during the electrospinning some SGNFWs were also prepared under elevated humidity conditions (R.H. up to 50/60%). Characterization. The crystalline phases of NFWs were identified by FT-IR in attenuated total reflection mode (A529-P/QMIRacle-ATR-unit) (Pike), (TENSOR II, Bruker). The XPS was performed by an instrument attached with Mg Kα X-ray source and a semispherical electron analyzer (Leybold−Heraeus). The crystallographic properties of the NFWs were studied using XRD patterns measured by X-ray diffractometer (Bruker, D8 Advance). The surface morphologies and diameters of the NFWs were studied with a FE-SEM; INSPECT F50 and HRTEM; JEOL, JEM-2100. The chemical composition and elemental mapping were obtained by using EDX spectroscopy recorded by using a Bruker Nano X-flash detector (410M) equipped with a FE-SEM chamber. The stress-strain measurements were performed by universal testing machine (Tinius Olsen H50KS) in order to study the mechanical properties of the NFWs where four specimens were tested for each NFW. The polarization (P)–electric field (E) hysteresis loops were acquired from the ferroelectric testing system (P-E, P-LC100V, Radiant Technology Precision) at room temperature. Dielectric properties were studied using a precision impedance analyzer (Wayne Kerr, 6500B) at room temperature.



Fabrication of the PONG. The PONG was basically fabricated via a simple sandwich like structure. The fabrication begins with the SGNFW placed in the middle as a piezoelectric component between two electrodes. The copper (Cu)–nickel (Ni) plated fine knit polyester fabric (Coatex Industries, India) with surface resistance of 0.05−0.1 /cm2 was used for top-bottom electrodes as shown in Figure 1. The conducting fabric was cleaned several times in ethanol, acetone, and deionized water in order to avoid any unwanted dust. After placing the textiles, the whole structure (top electrode/SGNFW/bottom electrode) was tightly sandwiched using a roller machine ensuring that there was no air-gap between the electrode and the piezo-active component. Finally, the edges are encapsulated by adhesive tape to make the structure more compact. Then, electrical leads were connected to the top and bottom electrodes. Performance characterizations. The piezoelectric performances of the PONG were recorded in terms of open-circuit output voltage using a digital storage oscilloscope (Tektronix TDS 2024C). A calibrated 3-axial force pressure sensor (Flexi-Force A201) was placed underneath the PONG to directly record the applied pressure. The output voltages from the PONG under wind and continuous mechanical impact measurements were performed using a National Instruments (NI) DAQ board (USB 6000) via LabVIEW interfacing with 1000 samples/s sampling rate. Shortcircuit current (Isc) were measured with a picoammeter (Keithley 6485). In wireless data transfer system, a photo diode (BPW34) was used as a receiver and IR Light Emitting Diode (LED) (TSHG8400) was used as an infrared (IR) transmitter. All the measurements were performed in 20-30 % humidity and 300 K temperature. To investigate the influence of the ambient humidity on the output performance of the PONG the relative humidity was increased up to 60% in selected experiments.


Page 32 of 60

Page 33 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information FT-IR spectra of SGNFW recorded under different humidity conditions, FE-SEM images of SGNFW prepared at different humidity conditions, Comparison table of present state-of-the-art device performance of the PNG in terms of nanofiber orientation, XRD patterns of the SGNFW in the range of 2θ ~ 30–60°, plot of polarization vs. electric field (P-E) and current density vs. electric field (J-E) of the PNFW, current density vs. electric field (J-E) of the SGNFW, strain (S) vs. P2 plot of the SGNFW, custom-built test bench for the PONG output characterizations, open circuit output voltage responses of the PONG by reversing the electrode connections, reverse connection condition of the PONG, output voltage from control device prepared in analogy to the PONG set-up and preparation and its enlarged view of the marked region, short-circuit current of the PONG and its enlarged view of the selected positive peak, several LEDs driving circuit (connected in series connection) and its respective I-V characteristic of powering up by the PONG, recorded output voltage response at an external load of 15 M and square of the output voltage, plot of the 1/VLvs. 1/RLand its linear fit to calculate the internal resistance of the PONG, enlarged view of the open circuit voltage in one cycle and response time (τR)of the PONG, table providing material properties of the SGNFW for finite element method (FEM) simulation, 3D-FEM model for simulation after meshing, capacitors charging circuit of the PONG, Open circuit output voltage responses of the PONG under different humidity conditions.

Notes The authors declare no competing financial interest.



ACKNOWLEDGEMENTS This work was financially supported by a grant from the Science and Engineering Research Board (SERB/1759/2014-15), Government of India. Kuntal Maity is thankful to UGC for his fellowship (No P-1/RS/319/14). Samiran Garain was partially supported by German Federal Ministry for Economic Affairs and Energy (BMWi, ZIM, 16KN033522).

REFERENCES (1) Zhao, G.; Zhang, X.; Cui, X.; Wang, S.; Liu, Z.; Deng, L.; Qi, A.; Qiao, X.; Li, L.; Pan, C.; Zhang, Y.; Li, L. Piezoelectric Polyacrylonitrile Nanofiber Film-Based Dual-Function SelfPowered Flexible Sensor. ACS Appl. Mater. Interfaces 2018, 10, 15855-15863. (2) Wang, Z. L.; Zhu, G.; Yang, Y.; Wang, S.; Pan, C. Progress in Nanogenerators for Portable Electronics. Mater. Today 2012, 15, 532 –543. (3) Maity, K.; Mandal, D. All-Organic High-Performance Piezoelectric Nanogenerator with Multilayer Assembled Electrospun Nanofiber Mats for Self-Powered Multifunctional Sensors. ACS Appl. Mater. Interfaces 2018, 10, 18257-18269. (4) Soin, N.; Shah, T. H.; Anand, S. C.; Geng, J.; Pornwannachai, W.; Mandal, P.; Reid, D.; Sharma, S.; Hadimani, R. L.; Bayramol, D. V.; Siores, E. Novel “3-D Spacer” All Fibre Piezoelectric Textiles for Energy Harvesting Applications. Energy Environ. Sci. 2014, 7, 1670− 1679. (5) Lee, S. H.; Jeong, C. K.; Hwang, G. T.; Lee, K. J. Self-powered Flexible Inorganic Electronic System. Nano Energy 2015, 14, 111 –125.


Page 34 of 60

Page 35 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Persano, L.; Dagdeviren, C.; Su, Y.; Zhang, Y.; Girardo, S.; Pisignano, D.; Huang, Y.; Rogers, J. A. High Performance Piezoelectric Devices Based on Aligned Arrays of Nanofibers of Poly(vinylidenefluoride-co-trifluoroethylene). Nat. Commun. 2013, 4, 1633 – 1643. (7) Sun, C., Shi, J., Bayerl, D. J., Wang, X. PVDF Microbelts for Harvesting Energy from Respiration. Energy Environ. Sci. 2011, 4, 4508 – 4512. (8) Steven, R. A.; Henry, A. S. A Review of Power Harvesting Using Piezoelectric Materials (2003–2006). Smart Mater. Struct. 2007, 16, R1– R21. (9) Almusallam, A.; Luo, Z.; Komolafe, A.; Yang, K.; Robinson, A.; Torah, R.; Beeby, S. Flexible Piezoelectric Nano-Composite Films for Kinetic Energy Harvesting from Textiles. Nano Energy 2017, 33, 146–156 (10) Schazmann, B.; Morris, D.; Slater, C.; Beirne, S.; Fay, C.; Reuveny, R.; Moyna, N.; Diamond, D. A Wearable Electrochemical Sensor for the Real-time Measurement of Sweat Sodium Concentration. Anal. Methods, 2010, 2, 342–348 (11) Koo, M.; Park, K. I.; Lee, S. H.; Suh, M.; Jeon, D. Y.; Choi, J. W.; Kang, K.; Lee, K. J. Bendable Inorganic Thin-Film Battery for Fully Flexible Electronic Systems. Nano Lett., 2012, 12, 4810–4816. (12) Yu, C. J.; Masarapu, C.; Rong, J. P.; Wei, B. Q.; Jiang, H. Q. Stretchable Supercapacitors Based on Buckled Single-Walled Carbon Nanotube Macrofilms. Adv. Mater., 2009, 21, 4793– 4797. (13) Xie, B. H.; Yang, C.; Zhang, Z. X.; Zou, P. C.; Lin, Z. Y.; Shi, G. Q.; Yang, Q. H.; Kang, F. Y.; Wong, C. P. Shape-Tailorable Graphene-Based Ultra-High-Rate Supercapacitor for Wearable Electronics. ACS Nano, 2015, 9, 5636–5645.



(14) Wang, Z. L.; Song, J. Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays. Science 2006, 312, 242 –246. (15) Qi, Y.; McAlpine, M. C. Nanotechnology-enabled Flexible and Biocompatible Energy Harvesting. Energy Environ. Sci. 2010, 3, 1275 – 1285. (16) Jeong, C. K.; Kim, I.; Park, K. I.; Oh, M. H.; Paik, H.; Hwang, G. T.; No, K.; Nam, Y. S.; Lee, K. J. Virus-Directed Design of a Flexible BaTiO3 Nanogenerator. ACS Nano 2013, 7, 11016 –11025. (17) Park, K. I.; Son, J. H.; Hwang, G. T.; Jeong, C. K.; Ryu, J.; Koo, M.; Choi, I.; Lee, S. H.; Byun, M.; Wang, Z. L.; Lee, K. J. Highly-Efficient, Flexible Piezoelectric PZT Thin Film Nanogenerator on Plastic Substrates. Adv. Mater. 2014, 26, 2514 –2520. (18) Alam, M. M.; Ghosh, S. K.; Sultana, A.; Mandal, D. Lead-free ZnSnO3/MWCNTs-Based Self-poled Flexible Hybrid Nanogenerator for Piezoelectric Power Generation. Nanotechnology 2015, 26, 165403−165408. (19) Huang, C. T.; Song, J.; Lee, W. F.; Ding, Y.; Gao, Z.; Hao, Y.; Chen, L. J.; Wang, Z. L. GaN Nanowire Arrays for High-Output Nanogenerators. J. Am. Chem. Soc. 2010, 132, 4766 – 4771. (20) Kholkin, A. L.; Pertsev, N. A.; Goltsev, A. V. Piezoelectricity and Crystal Symmetry. In Piezoelectric and Acoustic Materials for Transducer Applications; Safari, A., Akdogan, E. K., Eds.; Springer: New York, 2008. (21) Alam, M. M.; Mandal, D. Native Cellulose Microfiber-based Hybrid Piezoelectric Generator for Mechanical Energy Harvesting Utility. ACS Appl. Mater. Interfaces 2016, 8, 1555−1558.


Page 36 of 60

Page 37 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(22) Beevers, C. A.; McDonald, T.R.R.; Robertson, H. J.; Stern, F. The Crystal Structure of Sucrose. Acta Cryst. 1952, 5, 689−690. (23) Dittmar, J. H. Hygroscopicity of Sugars and Sugar Mixtures. Ind. Eng. Chem. 1935, 27, 333–335 (24) Maity, K.; Mahanty, B.; Sinha, T. K.; Garain, S.; Biswas, A.; Ghosh, S. K.; Manna, S.; Ray, S. K.; Mandal, D. Two-Dimensional Piezoelectric MoS2-Modulated Nanogenerator and Nanosensor Made of Poly(vinlydine Fluoride) Nanofiber Webs for Self-Powered Electronics and Robotics. Energy Technol. 2017, 5, 234 – 243. (25) Lovinger, A. J. Ferroelectric Polymers. Science 1983, 220, 1115−1121. (26) Ince-Gunduz, B. S.; Alpern, R.; Amare, D.; Crawford, J.; Dolan, B.; Jones, S.; Kobylarz, R.; Reveley, M.; Cebe, P. Impact of Nanosilicates on Poly(vinylidene fluoride) Crystal Polymorphism: Part 1. Melt-Crystallization at High Supercooling. Polymer 2010, 51, 1485−1493. (27) Martins, P.; Lopes, A. C.; Mendeza, S. L. Electroactive Phases of Poly(vinylidene fluoride): Determination, Processing and Applications. Prog. Polym. Sci. 2014, 39, 683−706. (28) Sencadas, V.; Gregorio, R.; Lanceros-Mendez, S. α to β Phase Transformation and Microestructural Changes of PVDF Films Induced by Uniaxial Stretch. Macromol. Sci., Part B: Phys. 2009, 48, 514 – 525. (29) Davis, G. T.; McKinney, J. E.; Broadhurst, M. G.; Roth, S. C. Electric-field-induced Phase Changes in Poly(vinylidene fluoride). J. Appl. Phys. 1978, 49, 4998. (30) Garain, S.; Sinha, T. K.; Adhikary, P.; Henkel, K.; Sen, S.; Ram, S.; Sinha, C.; Schmeiser, D.; Mandal, D. Self-Poled Transparent and Flexible UV Light-Emitting Cerium Complex−PVDF



Composite: A High-Performance Nanogenerator. ACS Appl. Mater. Interfaces 2015, 7, 1298−1307. (31) Chen, S.; Yao, K.; Tay, F.; Liow, C. L. Ferroelectric Poly(vinylidene fluoride) Thin Films on Si Substrate with the Phase Promoted by Hydrated Magnesium Nitrate. J. Appl. Phys 2007, 102, 104108. (32) Chang, C. E.; Tran, V. H.; Wang, J. B.; Fuh, Y. K.; Lin, L. W. Direct-Write Piezoelectric Polymeric Nanogenerator with High Energy Conversion Efficiency. Nano Lett. 2010, 10, 726− 731. (33) Mandal, D.; Yoon, S.; Kim, K. J. Origin of Piezoelectricity in an Electrospun Poly(vinylidene fluoride-trifluoroethylene) Nanofiber Web-Based Nanogenerator and NanoPressure Sensor. Macromol. Rapid Commun. 2011, 32, 831−837. (34) Garain, S.; Jana, S.; Sinha, T. K.; Mandal, D. Design of In Situ Poled Ce3+-Doped Electrospun PVDF/Graphene Composite Nanofibers for Fabrication of Nanopressure Sensor and Ultrasensitive Acoustic Nanogenerator. ACS Appl. Mater. Interfaces 2016, 8, 4532−4540. (35) Liu, X.; Ma, J.; Wu, X.; Lin, L.; Wang, X. Polymeric Nanofibers with Ultrahigh Piezoelectricity via Self-Orientation of Nanocrystals. ACS Nano 2017, 11, 1901−1910. (36) Huang, S.; Yee, W. A.; Tjiu, W. C.; Liu, Y.; Kotaki, M.; Boey, Y. C. F.; Ma, J.; Liu, T.; Lu, X. Electrospinning of Polyvinylidene Difluoride with Carbon Nanotubes: Synergistic Effects of Extensional Force and Interfacial Interaction on Crystalline Structures. Langmuir 2008, 24, 13621-13626. (37) Tamang, A.; Ghosh, S. K.; Garain, S.; Alam, M. M.; Haeberle, AJ.; Henkel, K.; Schmeisser, D.; Mandal, D. DNA-Assisted β‑phase Nucleation and Alignment of Molecular Dipoles in


Page 38 of 60

Page 39 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PVDF Film: A Realization of Self-Poled Bioinspired Flexible Polymer Nanogenerator for Portable Electronic Devices. ACS Appl. Mater. Interfaces 2015, 7, 16143 –16147. (38) Jana, S.; Garain, S.; Sen, S.; Mandal, D. The Influence of Hydrogen Bonding on the Dielectric Constant and the Piezoelectric Energy Harvesting Performance of Hydrated Metal Salt Mediated PVDF Films. Phys. Chem. Chem. Phys. 2015, 17, 17429−17436. (39) Yousry, Y. M.; Yao, K.; Chen, S.; Liew, W. H.; Ramakrishna, S. Mechanisms for Enhancing Polarization Orientation and Piezoelectric Parameters of PVDF Nanofibers. Adv. Electron. Mater. 2018, 4, 1700562. (40) Mandal, D.; Kim, K. J.; Lee, J. S. Simple Synthesis of Palladium Nanoparticles, β-Phase Formation, and the Control of Chain and Dipole Orientations in Palladium-Doped Poly(vinylidene fluoride) Thin Films. Langmuir 2012, 28, 10310−10317. (41) Brizuela, A. B.; Bichara, L. C.; Romano, E.; Yurquina, A.; Locatelli, S.; Brandan, S. A. A Complete Characterization of the Vibrational Spectra of Sucrose. Carbohydrate Research 2012, 361, 212–218. (42) Adhikary, P.; Mandal, D. Enhanced Electro-Active Phase in A Luminescent P(VDF– HFP)/Zn2+ Flexible Composite Film for Piezoelectric Based Energy Harvesting Applications and Self-Powered UV Light Detection. Phys. Chem. Chem. Phys. 2017, 19, 17789-17798. (43) Ico, G.; Showalter, A.; Bosze, W.; Gott, S. C.; Kim, B. S.; Rao, M. P.; Myung, N. V.; Nam, J. Size-dependent Piezoelectric and Mechanical Properties of Electrospun P(VDF-TrFE) Nanofibers for Enhanced Energy Harvesting. J. Mater. Chem. A 2016, 4, 2293 – 2304. (44) Hanson, J. C.; Sieker, L. C.; Jensen, L. H. Sucrose: X-ray Refinement and Comparison with Neutron Refinement. Acta Cryst. 1973, B29, 797–808.



(45) Yao, Y.; Wang, Q.X.; Wang, H.; Zhang, B.; Zhao, C.; Wang, Z.; Xu, Z.; Wu, Y.; Huang, W.; Qian, P.Y.; Zhang, X. X. Bio-Assembled Nanocomposites in Conch Shells Exhibit Giant Electret Hysteresis. Adv. Mater. 2013, 25, 711–718. (46) Ghosh, S. K.; Sinha, T. K.; Mahanty, B.; Mandal, D. Self-poled Efficient Flexible “Ferroelectretic” Nanogenerator: A New Class of Piezoelectric Energy Harvester. Energy Technol. 2015, 3, 1190−1197. (47) Alam, M. M.; Ghosh, S. K.; Sultana, A.; Mandal, D. An Effective Wind Energy Harvester of Paper Ash-Mediated Rapidly Synthesized ZnO Nanoparticle-Interfaced Electrospun PVDF Fiber. ACS Sustainable Chem. Eng. 2018, 6, 292−299. (48) Dahiya, A. S.; Morini, F.; Boubenia, S.; Nadaud, K.; Alquier, D.; Vittrant, G. P.Organic/Inorganic Hybrid Stretchable Piezoelectric Nanogenerators for Self-Powered Wearable Electronics. Adv. Mater. Technol. 2017, 1700249. (49) Chen, X.; Tian, H.; Li, X.; Shao, J.; Ding, Y.; An, N.; Zhou, Y. A High Performance P(VDF-TrFE) Nanogenerator with Self-Connected and Vertically Integrated Fibers by Patterned EHD Pulling. Nanoscale 2015, 7, 11536–11544. (50) Nadaud, K.; Morini, F.; Dahiya, A. S.; Justeau, C.; Boubenia, S.; Rajeev, K. P.; Alquier, D.; Vittrant, G. P.- Double Buffer Circuit for the Characterization of Piezoelectric Nanogenerators Based on ZnO Nanowires. Appl. Phys. Lett. 2018, 112, 063901−063901-5. (51) Ramadan, K. S.; Sameoto, D.; Evoy, S. A Review of Piezoelectric Polymers as Functional Materials for Electromechanical Transducers. Smart Mater. Struct. 2014, 23, 033001 – 033027. (52) Fang, J.; Wang, X.; Lin, T. Electrical Power Generator from Randomly Oriented Electrospun Poly(vinylidene fluoride) Nanofibre Membranes. J. Mater. Chem. 2011, 21, 11088– 11091.


Page 40 of 60

Page 41 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(53) Dhakras, D.; Borkar, V.; Ogale, S.; Jog, J. Enhanced Piezoresponse of Electrospun PVDF mats with a Touch of Nickel Chloride Hexahydrate Salt. Nanoscale 2012, 4, 752–756. (54) Fang, J.; Niu, H.; Wang, H.; Wang, X.; Lin, T. Enhanced Mechanical Energy Harvesting using Needleless Electrospun Poly(vinylidene fluoride) Nanofibre Webs. Energy Environ. Sci. 2013, 6, 2196 – 2202. (55) Zeng, W.; Tao, X.-M.; Chen, S.; Shang, S.; Chanb, H. L. W.; Choyb, S. H. Highly Durable All-fiber Nanogenerator for Mechanical Energy Harvesting. Energy Environ. Sci. 2013, 6, 2631– 2638. (56) Lee, B.- S.; Park, B.; Yang, H.-S.; Han, J. W.; Choong, C.; Bae, J.; Lee, K.; Yu, W.-R.; Jeong, U.; Chung, U-I.; Park, J.-J.; Kim, O. Effects of Substrate on Piezoelectricity of Electrospun Poly(vinylidene fluoride)-Nanofiber-Based Energy Generators. ACS Appl. Mater. Interfaces 2014, 6, 3520−3527 (57) Bafqi, M. S. S.; Bagherzadeh, R.; Latifi, M. Fabrication of Composite PVDF-ZnO Nanofiber mats by Electrospinning for Energy Scavenging Application with Enhanced Efficiency. J Polym Res 2015, 22, 130– 139. (58) Fuh, Y. K.; Kuo, C. C.; Huang, Z. M.; Li, S. C.; Liu, E. R. A Transparent and Flexible Graphene-Piezoelectric Fiber Generator. Small 2016, 12, 1875 – 1881. (59) Shi, K.; Sun, B.; Huang, X.; Jiang, P. Synergistic Effect of Graphene Nanosheet and BaTiO3 Nanoparticles on Performance Enhancement of Electrospun PVDF Nanofiber Mat for Flexible Piezoelectric Nanogenerators. Nano Energy 2018, 52, 153–162. (60) Baniecki, J. D.; Laibowitz, R.B.; Shaw, T.M.; Saenger, K.L.; Duncombe, P.R.; Cabral, C.; Kotecki, D.E.; Shen, H.; Lian, J.; Ma, Q.Y. Effects of Annealing Conditions on Charge Loss



Mechanisms in MOCVD Ba0.7Sr0.3TiO3 Thin Film Capacitors. J. Eur. Ceram. Soc. 1999, 19, 1457–1461. (61) Ikeda, T. Fundamentals of Piezoelectricity. Oxford University Press, Oxford, UK, 1996.


Page 42 of 60

Page 43 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(b)

(a) (c) Sugar H H

O CH2

O H

H

H2C O

O

O

O

PVDF Solution

O

Fructose

O

Glucose

H2C

H

H

H

F

F

F

C C H2

O

O

O

F

F

C C H2

H

F

F

C C H2

(f)

F

F

C C H2

F

F

C C H2

F C

C H2

(d)

(e) Conducting Fabric



Figure 1. Schematic illustration of PONG fabrication step by step. (a) Sugar particles incorporated into the PVDF-DMF solution. The enlarged view in the right side shows the schematics of interaction occurring in the PVDF solution due to H-bonding between the incorporated sugar and the CF2 dipoles of the PVDF chain. (b) Electrospinning process. (c) Optical image illustrating the prepared SGNFW in the omni-directionally stretched condition. (d) The 3D network structure of the SGNFW used for the PONG fabrication. (e) Top and bottom electrodes are realized by conducting fabrics. (f) The final structure of the PONG bearing connection of two electrical leads.


Page 44 of 60

Page 45 of 60

(c) as (CH2)

Absorbance (a.u.)

Absorbance (a.u.)

H bonded OH streching

SGNFW

PNFW

s (CH2) SGNFW

PNFW

3030 3000 2970 Wavenumber (cm-1)

3600 3300 3000 Wavenumber (cm-1)

(d) CF2

SGNFW

2

SGNFW PNFW

690 685 680 Binding energy (eV)

(f) O1s

C-O

Intensity (a.u.)

BE CF

C1s CH2

Intensity (a.u.)

SGNFW PNFW

F1s

695

(e)

O-C-O

SGNFW

C O F

Asymmetry

290 285 Binding energy (eV)

(g)

(h)

534 532 530 Binding energy (eV)

 SGNFW

 (110/200)

 (110) 



~ 56%

~ 3%



PNFW

tm ~ 158 C o

SGNFW

Absorbance (a.u.)

Absorbance (a.u.)

SGNFW

1.6

~ 59%

1500 1200 900 600 Wavenumber (cm 1)

(k) )

0.4 0.8 1.2 Energy (KeV)

(l)



1.0

180oC

(m)

PNFW

 (110/200)

 (110)

~ 53%

 (020)

~ 43%



30oC

1500 1200 900 600 Wavenumber (cm-1)

50

Intensity (a.u.)

SGNFW

536

(C-O) (C-O)

(j)

Absorbance (a.u.)

295

(i)

Normalised Intensity (a.u.)

(b)

(a)

Normalised Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100 150 ACS Paragon Plus Temperature (oC)Environment

~ 10%

15

20 25 2 (degree)

30


Figure 2. FTIR spectra of the PNFW and SGNFW in the region of (a) 3700–2900 cm─1, the marked region (3054─2952) cm─1 is shown in the enlarged view of (b). High resolution XPS spectra of the SGNFW and PNFW in the (c) F1s and (d) C1s core level regions. (e) Deconvoluted XPS spectra of O1s core level of the SGNFW. (f) EDX spectrum giving the atom fraction distribution in the SGNFW. Elemental mapping exhibiting (g) carbon (green), (h) oxygen (red), and (i) fluorine (blue) concentrations; scale bars correspond to 4m. (j) FT-IR spectra of the PNFW and SGNFW in the region of 1600–400 cm─1. (k) Change in absorbance intensity of the β-phase (1276 cm-1) vibrational band of the SGNFW as a function of temperature (30 oC–180 oC, thermal ramp ~ 1 oC/min for clarity) and its corresponding FT-IR spectra in 10 o

C intervals to guide the eye in inset, as recorded by in-situ temperature dependent FT-IR

spectroscopy. XRD patterns and their curve deconvolution of the (l) SGNFW and (m) PNFW; points show the experimental data, and the solid lines correspond to the best fit.


Page 46 of 60

Page 47 of 60

10 5 0

200 300 400 Fiber diameter (nm)

500

10 5 0

Expt data Fitted data

FFT Intensity (a.u.)

(b) SGNFW

(c)

15

Frequency

(a) PNFW

Frequency

100 150 200 Fiber diameter (nm)

0

SGNFW

60 120 Polar Angle (Degree)

180

SGNFW

(d)

(f)

(e) SGNFW

6 Stress (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SGNFW PNFW

(g) 3

0 0

20 40 Strain (%)

60

(h)

Figure 3. FE-SEM images of (a) PNFW and (b) SGNFW; the diameter distributions of the nanofiber webs are shown in respective inset; scale bars correspond to 5 m. (c) Radial intensity



distribution vs alignment angle (0–180o) for randomly networked SGNFW with its 2D FFT image shown in the inset. (d) TEM image, right upper inset shows the HR-TEM image and left lower inset shows the corresponding SAED pattern of the SGNFW; scale bars correspond to 200 nm, 20 nm and 10 1/nm respectively. (e) Mechanical response of the SGNFW and PNFW. Nature of flexibility of SGNFW is shown by (f) rolling, (g) twisting and (h) folding, respectively.


Page 48 of 60

Page 49 of 60

(b)

0.04

SGNFW

0.2

SGNFW

Strain (%)

2

Polarisation (C/cm )

(a)

0.0

0.02

0.00 -0.2 -20

-20 0 20 Electric field (kV/cm)

0 20 Electric field (kV/cm)

(d)

15

10

5 3

10

4

5

10 10 Frequency ( Hz)

0.2 SGNF W

SGNFW P NFW

Dielectric loss (tan )

(c) Dielectric constan ( r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10

6

PNFW

0.1

0.0

3

10

4

5

10 10 Frequency (Hz)

Figure 4. (a) Polarization vs. electric field (P-E) and (b) butterfly shaped strain vs. electric field (S-E) hysteresis loops of the SGNFW. Frequency dependent dielectric properties (c) dielectric constant (εr) and (d) loss tangent (tan δ) of the PNFW and respectively.


10

6


a

PONG

Voltage (V)

80

a

~ 5 kPa

~ 10 kPa

a

~ 1kPa

80

Sm~ 7.2 V/kPa

40

4 8 Pressure (kPa)

12

Press

40

a ~ 5 kPa

a ~ 1 kPa

Release

-40 0

5

10 15 Time (s)

20

-40 0

25

(d) Current (A)

3 Touch

0 Release

-3

2

3 4 5 Time (s)

15

6

4 0 -4

7

(e)

(f)

35

Power (mW/m )

1

10

8

-8 0

-6 0

5 Time (s)

6

Voltage (V)

a ~ 10 kPa

0

0

(c)

Ref. PNG

80

0

40

(b) 120

Exp Data Linear fitting

Voltage (V)

120

Voltage (V)

(a)

30

20

40 Time (s)

60

10 20 30 Resistance (M)

40

6

Current (A)

2

80

Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 50 of 60

60

4

25 20

40 2 10

20 30 Resistance (M)

40

15 0


Page 51 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Open circuit output voltage responses for different applied human finger impact for the (a) PONG and (b) Ref. PNG. The enlarged marked area in (a) is shown in the lower inset while the upper inset shows the output voltages of the PONG as a function of applied pressure. (c) Output voltage response for the impact of drum beats of a toy; enlarged marked area is shown in the middle inset; upper inset shows the demonstration and lower inset shows a photograph of response respectively. (d) Measured short-circuit output current response under the human finger impact of 10 kPa. (e) Dependences of output voltage and current on variable external load resistance with schematic circuit diagram in the inset. (f) Instantaneous output power density of the PONG as a function of variable load resistance; the upper and lower insets show the glowing array of several LEDs (blue and green) by direct finger touch without using any external power source.



Page 52 of 60

(b)

(a)

(001) (0-11) H

(-101)

(-1-11)

O

(-1-10)

(-100)

(110)

C

(-10-1)

(c)

Original State No e- flow

(d)

118.73

Pressing e- flow

Releasing e- flow

Piezopotential (V)

0.0461

(e)

(f)

0.4806

0 Surface charge density (C/m2)

-52.86

-0.0477


Displacement (m)

Page 53 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. (a) Molecular structure of sugar i.e. sucrose consisting of glucose and fructose and (b) typical shape of a sucrose crystal with assigned main planes indicated by arrow marks. (c) Schematic showing the working mechanisms under original, pressing and releasing state of the PONG. Simulation results of the (d) piezovoltage distribution, (e) surface charge density distribution and (f) deformation distribution (the solid black line indicates the original position before deformation) of network structured SGNFW at a constant external stress amplitude of 10 kPa.




Page 54 of 60

Page 55 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Vibrational response from PONG. (a) Schematic illustration of wind blowing setup from an air blower and continuous data acquisition from computer control system. Real-time voltage signal response of the PONG to wind blowing with (b) different distance, (c) different air velocity and (d) different effective area of the PONG respectively (The corresponding insets show the voltages as a function of distance, velocity and effective area, respectively). (e) Real-time voltage signal response during massage belt vibration (“OFF” and “ON” conditions) from the PONG. The inset shows the photograph where the massage belt is attached to human body. (f) Voltage signal in response to various musical instruments in operation (violin, piano, guitar and kick drum). The inset scheme shows the corresponding setup in front of a sound speaker.



(a)

(b) 1F

1.5 ON

OFF

2.2F 4.7F

4

0 0

Power (W)

Voltage (V)

8

1.0 0.5 0.0

40 Time (s)

1 F

80

2.2 F

4.7 F

Photodiode

(c)

Transmitted signal (V)

(d) LED

Vt

PONG

RL

Transmitter

Receiver

20

0

0

(e)

(f) Output Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 56 of 60

1

2 3 Time (s)

4

5

20 15 Before 10 weeks

After 10 weeks

10 5 0


0

2

4 6 8 Number of Weeks

10

Page 57 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. (a) Capacitor (1, 2.2, and 4.7 F) charging response driven by the PONG and (b) the power stored in the respective capacitors. The upper inset shows that a LCD screen is powered up (‘OFF’ to ‘ON’ state) directly from the charged capacitor. (c) Schematic circuit diagram of wireless detection of the transmitter–receiver system driven by the PONG via an IR-LED and a photodiode. (d) The enlarged form of transmitted signal from the receiver when the PONG drives the transmitter. (e) Fatigue test: open-circuit voltage recorded over time in response to continuous impacting over 24,000 cycles with frequency of 3Hz under the pressure of 0.9 kPa. (f) Stability and durability test results of the PONG during 10 weeks. In the inset SEM images (initial and after 10 weeks) show that no obvious distortion or serious damage was observed on the SGNFW structure after continuous mechanical impact; scale bar corresponds to 1 μm (insets).



Page 58 of 60

Table 1: An extensive comparison between the output performances of our fabricated PONG and those of PNGs based on PVDF NFW. (Here‚ t: thickness of the piezoelectric material, A: working area of the piezoelectric material, d: separation length between two electrodes, NF: not found, NA: not applicable)

Name of Additive

Type of Additive

Applied Force/Freque ncy/Pressure

Device Dimensions

Device Output Impedance Voltage (V)

Reference

NA

─

2-4 Hz

d= 100-600 m

15 G

0.005-0.03

[32]

NA

─

10 Hz

t = 140 m,

NF

6.3

[52]

NF

0.76

[53]

NF

2.6

[54]

A= 2 cm2 NiCl2, 6H2O

Inorganic

950 ±30 

t = 0.1 mm, A= 100 mm2

NA

NaNbO3

─

Inorganic

10 Hz,

t = 100 m,

10 N

A= 2 cm2

1 Hz,

t = 162 m, A= 6.3 cm2

NF

3.2

[55]

t= NF,

NF

0.78

[56]

41 M

1.1

[57]

0.2 MPa

NA

─

100 Hz

A= 775 mm2

ZnO

Inorganic

75 kHz

t= 120 m, A= 4 cm2


Page 59 of 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


NA

─

4 Hz

t= NF,

~ M

2.5

[58]

NF

11

[34]

NF

14

[24]

NF

11

[59]

NF

4.8

[47]

13.5 M

100

this work

A= 6.3 cm2 Ce3+/ Graphene

MoS2

Inorganic

Inorganic

4 Hz

t= NF,

8N, 6.6 kPa

A= 1200 mm2

7 N, 8.8 kPa

t= 150 m A= 93.5 cm2

Graphene - Inorganic BaTiO3

t= 18-20 m 2 Hz A= 6.3 cm2

ZnO

t= 150 m

Inorganic 145 Pa

A= 82.7 cm2 Sugar

Organic

10 kPa

t= 150 m A= 108 cm2



ToC Graphic


Page 60 of 60

Natural Sugar Assisted Chemically Reinforced Highly Durable Piezo

Recommend Documents