Highly Flexible Mechanical Energy Harvester Based on Nylon 11

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Highly Flexible Mechanical Energy Harvester Based on Nylon 11 Ferroelectric Nanocomposites Farsa Ram, Sithara Radhakrishnan, Tushar Ambone, and Kadhiravan Shanmuganathan ACS Appl. Polym. Mater., Just Accepted Manuscript • DOI: 10.1021/acsapm.9b00246 • Publication Date (Web): 08 Jul 2019 Downloaded from pubs.acs.org on July 21, 2019

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ACS Applied Polymer Materials

Highly Flexible Mechanical Energy Harvester Based on Nylon 11 Ferroelectric Nanocomposites Farsa Ram,1,2 Sithara Radhakrishnan,1 Tushar Ambone,1 Kadhiravan Shanmuganathan1,2* 1Polymer

Science and Engineering Division, CSIR-National Chemical Laboratory, Dr. Homi

Bhabha Road, Pune, Maharashtra-411008, India. 2Academy

of Scientific and Innovative Research, CSIR-National Chemical Laboratory, Dr.

Homi Bhabha Road, Pune, Maharashtra-411008, India. Keywords: Cellulose nanocrystals, nanogenerator, piezoelectric, ferroelectric, nylon 11, nanocomposite, Abstract: We report here a flexible piezoelectric energy harvester using castor-oil derived nylon 11 and biomass derived cellulose nanocrystals (CNC). Using a simple solution casting process, we were able to fabricate flexible large area nylon 11 and composite films. Neat nylon 11 films crystallized predominantly in α- phase. Incorporation of CNC at a low concentration of 2-5 wt% resulted in almost complete transition of α-phase to polar γ-phase, which could be attributed to strong hydrogen bonding interactions between CNC and amide groups in nylon 11. This remarkable shift in crystallization behavior also led to enhanced piezoelectric performance. We also found that addition of 5 wt% glycerol (on the dry weight of nylon 11 or composite) enhanced the flexibility of the film. Energy harvesting devices made from 5 wt% nylon 11/CNC films showed about 2.6 times higher output voltage as compared to neat nylon 11 devices under similar impact conditions and the effect was durable over 800 cycles. These devices were also used to charge a 10 µF polarized capacitor and we found that the 5 wt% nylon 11/CNC devices charged up to 3.78 V in 90 seconds, which is 2.8 times higher than nylon 11 devices. To the best 1 ACS Paragon Plus Environment

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of our knowledge, this is the first report on nylon 11 nanocomposites, where cellulose nanocrystals have been used to enhance the electroactive γ or δ’ phase in nylon 11 and yield such high piezoelectric performance.

Introduction: Energy harvesting from mechanical vibrations has been an area of tremendous interest for powering portable and wearable electronic devices. Piezoelectric and ferroelectric materials (a subclass of piezoelectric materials having unique polar axis that can be reoriented by the application of an electric field) manifest a change in electrical polarization in response to mechanical stress. This polarization change leads to surface charges that can be harvested and used as a source of power. 1 Ceramic materials such as lead zirconium titanate (PZT), barium titanate etc. exhibit a very strong piezoelectric effect with a high piezocoefficient (d31~ 100-300 pC/N), while polymer based piezomaterials have an order of magnitude lower piezocoefficient (d31~ 20-30 pC/N). Nonetheless, polymeric piezoelectric materials have many advantages such as the ability to undergo larger mechanical strain, easy processability, low density, flexibility, scalability for large area application etc. Some of the polymers known for exhibiting piezoelectric effect include poly(vinylidene fluoride) (PVDF)1 and their co-polymers,2 odd nylons,1 poly(lactic acid)3 and cellulose4. Among all polymers, PVDF and their co-polymers exhibit the highest electromechanical response at room temperature and have been studied extensively for various applications such as, pressure/strain sensors, actuators, nanogenerators etc.5,6,7,8,9 Nylon-11, a castor oil derived polyamide is also known to exhibit piezoelectric effect. However, it has been a less explored polymer relative to PVDF. Nylon 11 belongs to the family of odd nylons with molecular repeat unit –HN-(CH2)2nCO-. Herein, the carbonyl and amine groups in two adjacent chains are favorably placed so as to maximize hydrogen bonding and 2 ACS Paragon Plus Environment

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preferred alignment of dipoles resulting in maximum net polarization.10 The even numbered nylons pack in such a way that the dipole moment associated with hydrogen bonds are cancelled. Odd nylons usually have at least three stable polymorphs, i.e., triclinic α form, pseudohexagonal γ form and hexagonal δ form. They are inter-convertible upon suitable treatments such as vapor phase deposition,11 uniaxial stretching,12 melt quenching,13 cold drawing,14 and spin coating15. Nylons are moisture sensitive and hence difficult to handle in normal conditions. This problem can be addressed by increasing the number of methylene groups between the amides, but this also increases the distance between the dipoles, which results in reduced polarization and piezoelectricity. New strategies to enhance polar crystal phases and piezoelectricity of nylon 11 would favor the development of flexible mechanical energy harvesters based on bio-based polymers. Although several reports are available on nylon 11 composites including additives such as PZT16, BaTiO3,17 CaCu3Ti4O12,18 and NaNbO3,19 etc. there is no information on any crystal phase change in nylon 11 in the presence of these additives. The ceramic particles contribute primarily to the dielectric properties and nylon 11 has been used here as a flexible matrix. Huang et al.20 have shown that incorporation of MWCNT induces the formation of αphase, which is a less polar crystal phase as compared to γ-phase. Blends of PVDF21,22 and nylon 11 have also been reported, wherein it is shown that using maleic anhydride copolymer as compatibilizer helps to attain high dielectric constant with low dielectric loss. There are few reports on nylon 11/nanocellulose composites where the primary focus is on mechanical and morphological characteristics of the composites and not on piezoelectric properties.23,24,25 Notwithstanding the extensive literature available on PVDF based ferroelectric energy harvesters, there has not been much investigation on nylon 11 based energy harvesting materials. In fact, the only recent report that demonstrates energy harvesting performance of nylon 11 is

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that of Kar-narayan et. al. where nylon 11 nanowires have been prepared using anodized aluminum oxide template. The nylon 11 NWs based piezoelectric nanogenerator was used to harness the vibrational energy and produce ~1 V when exposed to low amplitude vibrations.26 We report here a simple and facile approach to enhance the piezoelectric phase in nylon 11 using cellulose nanocrystal (CNC). This approach has been used to fabricate flexible large area films and energy harvesting devices from nylon 11 nanocomposites with output voltage as high as 6.95 V. To the best of our knowledge, this is the first report on nylon 11 nanocomposites where cellulose nanocrystals have been used to enhance the electroactive γ or δ’ phase in nylon 11 and result in high piezoelectric performance.

Experimental: Preparation of Cellulose Nanocrystals (CNCs):27,28 Cellulose suspension (20 mg/mL) was prepared by combining 7 g of Whatman No.1 filter paper with 350 mL of DI water and blended at high speed until a lumpy pulp of homogenous nanocellulose was formed. Then 12N HCl was added drop wise to the cellulose pulp to result in a final concentration of 3N at 0 oC. Further, the suspension was heated to 80 oC and maintained for 3 h. Then the reaction mixture was cooled down to ~ 25 oC, filtered and washed with DI water until the obtained supernatant was neutral. As obtained acid hydrolyzed nanocellulose was dispersed into DI water (20 mg/mL) and 0.7 g TEMPO and 7 g of NaBr were added to the mixture. After 5 min of stirring, 1.75 g of NaClO was added and the pH of the solution was adjusted to 10-11 with 3N NaOH (Scheme 1). The mixture was stirred for 4 h at room temperature. After 4 h, 42 g of NaCl was added to the reaction mixture to precipitate the suspension. Finally, the CNCs were washed with 0.5-1M NaCl by centrifugation and washing procedure was repeated three to four times to remove any remaining 4 ACS Paragon Plus Environment

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Scheme 1: Preparation of cellulose nanocrystals.

NaClO. The carboxylates were converted into free acid form by two more washing cycles with 0.1N HCl. Finally, the product was dialyzed with deionized water for 3 days and then subjected to lyophilization. The carboxyl content was determined by conductometric titration and found to be ~600 mmol/kg (Figure S1). Solution Casting of Nylon 11/CNC film: Nylon 11 (NY henceforth) pellets were dried at 80 ˚C under vacuum for 24 h prior to dissolution in formic acid by constant stirring at 100 ˚C for 2 h. Pre-calculated amount of CNC (2 wt% and 5 wt% with respect to dry weight of nylon 11) was added to formic acid and dispersions were prepared by sonication for 30 min. These dispersions were mixed with nylon 11 solutions for preparing various composites. The total solid content in all the solutions was maintained as 30 wt%. The solutions were vortex mixed and poured into Teflon petridishes. The films were kept for drying at room temperature overnight and further dried under vacuum at 60 oC for 12 h. The nylon 11/CNC composites are labeled as follows: 2NYC refers to 2 wt% CNC in nylon 11 and 5NYC refers to 5 wt% CNC in nylon 11. These solution casted films were brittle in nature (see scheme S1). As an approach to make flexible films, we added 5 wt% of glycerol (on the dry weight of nylon 11 or composite) as plasticizer to NY or 5NYC composite solutions and heated the solutions at 100 ˚C with stirring for 30 min (Scheme 2). Finally, the solutions were poured on a glass plate and drawn into uniform thickness 5 ACS Paragon Plus Environment


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Scheme 2: Preparation of Nylon 11 and their composite films.

films with a doctor blade. The films were dried under similar conditions as solution cast films and peeled off for fabrication of flexible nanogenerators. Characterization of Surface Modification and Phase Transformation: CNCs were characterized using Attenuated Total Reflectance- Fourier Transformed Infrared Spectroscopy (ATR-FTIR) to determine the carboxyl modification. The NY and NYC composites were also characterized for any detectable chemical changes after the addition of CNC. All the measurements were done with 32 scans at 1 cm-1 resolution on Perkin Elmer’s FTIR instrument (Spectrum GX Q5000IR). Room temperature Wide Angle X-ray Diffraction (WAXD) was performed on CNC, NY and NYC composites to determine changes in crystalline morphology. The Rigaku MicroMax-007 HF equipped with rotating anode was operated at 40 kV and 30 mA with copper X-ray source having wavelength λ (Cu Kα) =1.54 Å. As obtained 2-D diffraction patterns were converted to 1-


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D profiles after background subtraction using Rigaku 2DP software and scattered intensity was plotted against 2θ in the range of 2 – 40°. Crystallinity Analysis: The melting transition temperature (Tm), glass transition temperature (Tg), and heat of fusion (ΔHm) of NY and NYC composites were determined by Q10 differential scanning calorimeter (TA Instruments) under a nitrogen purge stream of 50 mL/min. Only single heating was performed and samples were heated from 20°C to 220 °C at the rate of 10 °C/min in aluminum pans. The crystallinity value was calculated by following Eq. χc (%)=ΔHm/(∆Hm° (1-Φ)) ×100 Where ∆Hm is the melting enthalpy (in J/g) of sample and ∆Hm° is the enthalpy of melting for a 100% crystalline NY sample. Φ is the percentage weight fraction of CNC in the CNC/nylon 11 composites. The melting enthalpy of 100% crystalline nylon 11 used for the calculation was 206 J/g.29 Mechanical and Viscoelastic Properties: Stress-strain tests were performed on 20 mm X 4 mm rectangular strips of NY and NYC composite films having thickness about 0.08 mm. The strain rate was fixed at 0.05 mm/s and strain was plotted against stress to get the values of ultimate tensile strength and the strain at break. The storage modulus (E’) and loss modulus (E’’) of the films were ascertained by dynamic time sweep, where E’ and E’’ was recorded over a period of time at 0.05% strain, 25 °C, and 1 Hz frequency using a dynamic mechanical analyzer (RSA 3, TA instruments). Corona poling:1 The NYG and 5NYCG films were poled using corona triode. The samples were placed on a heating plate, where temperature was maintained to 60 ºC for 10 min. 18 kV electrical filed was applied to needle which was placed 4 cm above the samples. To ensure 7 ACS Paragon Plus Environment


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uniform distribution of corona charges, a mesh (at 4kV) was placed between the samples and needle, at 1 cm height from samples. Fabrication of Flexible Piezoelectric Nanogenerators: Piezoelectric nanogenerator devices were prepared by attaching adhesive copper tapes on both the surfaces of flexible nylon 11 and composites. Thin copper wires were soldered to the copper electrodes. Finally, the devices were encapsulated in an insulating matrix to minimize device damage and electrostatic charge contribution while testing (see Scheme S2). Piezoelectric Properties: Energy generation measurements were carried out using an in-house fabricated impact machine.30 The devices were tested at ~23 N force measured using a Flexiforce sensor (Teckscan A450). The output response of the piezoelectric generator was measured using Tektronix make Mixed Signal Oscilloscope (Model no. MSO2024 16CH MSO) having maximum sampling rate of 1GS/s and frequency range up to 200 MHz.

Results and Discussions: The carboxyl modification of CNC by TEMPO mediated oxidation of primary hydroxyl groups was confirmed using ATR-FTIR. The peak at 1724 cm-1 which corresponds to the carbonyl group of carboxylic acid confirms the presence of surface carboxylic groups (Figure S2). Carboxylated CNCs were easily dispersible in water by sonication, and have a diameter of about 20-50 nm and length about 200-1000 nm as shown in TEM image (Figure S3). The crystalline phase changes in NY and NYC were confirmed using WAXD. Nylon 11 films obtained by solution casting using formic acid yielded both  and  phases.29 The α-phase of nylon 11 typically appears at 2θ = 7.54º, 19.92º, and 20.14º, 22.8º, 23.74º, 24.2º and the γ-phase nylon 11 appears at 2θ = 5.91º, 21.6º.26,29,31,32,33 We observed that solution casted films of NY resulted 8 ACS Paragon Plus Environment

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Figure 1: a) WAXD, b) and c) FTIR analysis of solution casted nylon 11 and their composite films.



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mostly in α-phase, with peaks appearing at 7.7, 19.97 and 23.95 º and small γ-phase peak appearing at 6.24º and 21.6º. The intensity of the α-phase peak decreased after addition of 2 wt% CNC and almost completely diminished at 5 wt% CNC, while the polar γ-phase peak at 21.6º became very predominant (Figure 1a). CNCs seem to have a strong influence on the crystalline phase transitions in nylon 11 which has not been reported elsewhere. This could be attributed to strong hydrogen bonding interactions between CNCs and amine groups in nylon 11. In the room temperature FTIR analysis of Nylon 11, the different crystal phases appear too close to distinguish. However, there are few bands which can be resolved.34 The FTIR peak assignment of the different phases of nylon 11 is listed in Table S1.34 In the solution casted films of NY, 2NYC and 5NYC weak bands at 627 cm-1 and 709 cm-1 are observed, which corresponds to γ-phase of nylon 11. The CH2 wagging band which appears at 1190 cm-1 for α-phase of nylon has shifted to 1198 cm-1 after addition of CNC. The band at 1198 cm-1 corresponds to the γ-phase of the nylon 11 (Figure 1b). Another, distinguished difference can be observed in crystalline NH stretching band (amide A band) which appear at 3303 cm-1 for α-phase and at 3297 cm-1 for γphase. The shift in amide A band to 3297 cm-1 is indicative of γ-phase of Nylon 11and can be seen clearly in 2NYC and 5NYC (Figure 1c). Further increase in concentration of CNC to 8 wt % led to the reappearance of α-phase as shown in Figure S4. This could be due to agglomeration of CNC at higher concentrations. Properties related to crystallinity of the solution casted films were studied using differential scanning calorimetry. The effect of processing parameters on the thermal and crystalline properties were studied using first heating cycle. No drastic change in melting temperature (Tm) could be observed after addition of CNC (as shown in Figure S5). The crystallinity of solution casted NY film was about 56.7% (SD = 1.5%) which increased to 58.7 % (SD = 0.1%) in 10 ACS Paragon Plus Environment

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Figure 2: a) Solution casted NYC film; solution drawn NYC film, b) normal state, c) folded, d) rolled,

e)

multi

folded

and

f)

large

area

film.

2NYC and to 63 % (SD = 1.1%) in 5NYC. The melting temperature (Tm) increased to 191.3 ºC and 190.4 ºC for 2NYC and 5NYC, respectively from 190.10 ºC of neat nylon 11. Since the CNCs seemed to have a very strong influence on α to γ phase transition in nylon 11 with slight changes in overall crystallinity, we were interested in making large area films and evaluating the piezoelectric performance. However the brittle nature of films (Figure 2a) made it difficult to fabricate free standing robust films. To overcome this issue, we added a small amount of glycerol (refer experimental section) to nylon 11 and nylon 11/CNC solutions to render flexibility to the films. Instead of solution casting, the solution was drawn on a glass plate using a doctor blade. This helped to prepare uniform thickness films of large area (Scheme 2).



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Figure 3: a) WAXD, b) and c) FTIR analysis of solution drawn nylon 11 and their composite films.


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FE-SEM analysis revealed no significant difference in the surface morphology or cross section of the NYG and 5NYCG films (Figure S6). The solution drawn films were flexible in nature and can be bent, rolled or multi folded as shown in Figure 2b to 2e. Moreover, this method can produce large area films as shown in Figure 2f. The films were porous in nature and incorporation of CNC did not change the surface morphology of the nylon 11 films significantly (Figure S6) In WAXD (Figure 3a), the solution drawn nylon 11 (NYG) films exhibited α-phase as predominant phase at 7.7º, 20.14 º and 23.95 º. Additionally, solution drawn NYG film showed a small peak at 21.6 º which corresponds to γ -phase of Nylon 11. The glycerol plasticized 5NYC (5NYCG) film manifested a low intensity γ-phase peak at 5.95º and a predominant γ-phase peak at 21.6ºand the α-phase peaks at 20.14 and 23.95 º were almost diminished. Figure 3b and 3c shows the FTIR spectrum of solution drawn NYG and 5NYCG flexible films. In solution drawn flexible NYG film, the α-phase bands appeared at 1126 cm-1 and 3309 cm-1 which shifted to γ-phase bands at 1123 cm-1 and 3297 cm-1 in 5NYCG. It clearly illustrates that the addition of glycerol did not have any adverse effect on the γ-phase nucleation in NYCG films. CNCs disperse very well in formic acid due to carboxyl groups and remain in acid form in acidic media. Similarly, nylon 11 could also be dissolved easily in formic acid. Amine group of nylon 11 can interact with acid/hydroxyl group of CNC via hydrogen bonding interactions or electrostatic interaction as shown in the Figure 4a. These interfacial interactions are strong enough to remain as the formic acid evaporates and the film is formed. The presence of interfacial interaction can be confirmed with the FTIR bands of symmetric (2849 cm-1) and asymmetric (2918 cm-1) stretch of methylene group (-CH2) of nylon 11. As mentioned in earlier reports, in the presence of interfacial interactions these bands shift to lower wavenumber



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region.35 This is evident in Figure 4, where the symmetric and asymmetric stretch of methylene group (-CH2) shifted to 2848 cm-1 and 2917 cm-1, respectively.

Figure 4: a) Schematic representation of possible interaction between nylon 11 and CNC and b) shift in -CH2 symmetric and asymmetric bands due to these interfacial interactions. The solution drawn flexible films (NYG and 5NYCG) exhibited a slightly lower crystallinity (47.2% (SD =0.27%) and 49.3% (SD = 1.5%)) than solution casted films which could be due to the effect of plasticizer. Tm of 5NYCG film increased to 187.50 ºC from 184.39 ºC of NYG film (Figure S7). Similar trends have been observed with addition of acid hydrolyzed microcrystalline cellulose into nylon 11 melt pressed films, where Tm increased from 188.5 ºC to


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189.1 ºC and crystallinity increased from 23.2% for neat nylon to 26.6% after the addition of 5 wt% acid hydrolyzed MCC.24 Rohner et. al. reported slight (0.1-0.3%) increase in crystallinity of nylon 11 with doping of 0.1-0.5 wt% of cellulose nanofibers.25 These results suggest that the melt pressed films have very low crystallinity which is not ideal for nanogenerator application. Moreover, these melt pressed films have very low polar γ- phase content, which is very essential to realize the piezoelectric properties of nylon 11.The flexibility of solution drawn films was also investigated using dynamic mechanical analyzer. The NYG film had ultimate tensile strength of 10.29 MPa, which increased to 16.04 MPa after addition of 5 wt% CNC as shown in Figure 5a. Addition of nanoclay,36 or cellulose nanofibers24,25 into nylon 11 matrix has been found to result in similar enhancement in the ultimate strength and decrease in the strain at break. It should be noted that the films are highly

Figure 5: a) Stress-strain curve and b) storage and loss modulus for NYG and 5NYCG films.

flexible and show a strain at break of 7.8% for NYG and 7.2% for 5NYCG film which is much higher than that of ceramic piezoelectric films (e.g. PZT, BaTiO3) which break below 1% strain.37 The storage modulus (E’) and loss modulus (E’’) of the 5NYCG film are relatively 15 ACS Paragon Plus Environment


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higher compared to NYG film. The NYG film revealed E’ and E’’ of 0.41 and 0.22 GPa which increased to 0.55 and 0.29 GPa, respectively in the case of 5NYCG (Figure 5b). The strong influence of CNC in inducing polar γ- phase crystallization in nylon 11 encouraged us to evaluate the piezoelectric properties of nylon 11/CNC composites. Energy harvesting devices were fabricated from as prepared and corona poled flexible films. These devices were tested using in-house fabricated impact machine and the applied force was tracked using a Flexi

Figure 6: Voc of flexible films based PENG, a) NYG, b) 5NYCG and c) durability test of 5NYCG PENG.


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Figure 7: Output voltage of poled PENGs after three months of storage, a) NYG and b) 5NYCG.

force sensor. The un-poled 5NYCG device resulted in peak to peak open circuit voltage (Voc) of 2.3 V, while neat NYG resulted in only about 0.7 V as shown in Figure 6a and 6b.After corona poling of the films, the Voc significantly increased, where NYG and 5NYCG films showed the Voc of 2.68 and 6.95 V, respectively at ~23 N force. Thus 5NYCG films exhibited a remarkable 2-3 fold improved piezo performance over the NYG films. This is due to improved γ-phase and crystallinity of nylon 11 after addition of CNC. To the best of our knowledge, there is no direct report on film based large area flexible piezoelectric nanogenerators using nylon 11. Nylon 11 nanowire based PENG for vibrational energy harvesting resulted in the output voltage of 1V.26 Dhanalakshmi et. al. fabricated an electrospun 5 wt% nylon 11/ZnO based piezoelectric 17 ACS Paragon Plus Environment


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nanogenerator and the output voltage was ~1.2V, whereas neat nylon 11 electrospun mat resulted in 0.3 V (force information not mentioned in the report).38 It should also be noted that the films made by this process were mechanically robust yielding durable piezo output over 800 cycles. As shown in Figure 6c, Voc of initial few cycles and last few cycles are almost constant. We also checked the device durability after three months of storage. The output performance of these films was found to be similar to freshly prepared films. As shown in Figure 7a & 7b, the poled NYG and 5NYCG PENGs resulted in Voc of 2.65 V and 6.87 V, respectively. The peak to peak output voltage is sufficiently high or comparable to other polymeric PENG e.g. 2wt% Fe-doped RGO/PVDF (5.1 V when imparted with human finger),39 8wt% dabcoHReO4/PVDF (6.4 V at 6N force),40 0.20 wt% rGO/PVDF (3 V at 0.5N force)41 etc. As shown in the Figure S8, at this energy harvesting conditions, the NYG and 5NYCG device had a maximum power output of ~90 and 500 µW/cm3 (820 kΩ resistor), respectively which is sufficient to power light emitting diodes, small sensors or devices and to charge capacitors for various small power applications. In order to demonstrate a practical application, we also charged a polarized capacitor using PENG and a bridge rectifier circuit (BRC). The current from the PENGs is an alternate current and has to be converted into direct current before connecting to the polarized capacitor. BRC (Figure 8a) helps to convert the AC input in to DC output which is stored by capacitor and can be measured as accumulated voltage using multimeter. We have used 10 µF polarized capacitor and charged it using NY and 5NYC PENG. The charging rate and voltage on capacitor was higher for 5NYCG device as shown in Figure 8b. After 90 seconds the charging became almost constant where 5NYG charged the capacitor up to1.35 V and 5NYCG charged it up to 3.78 V, which is 2.8 times higher than NY PENG. 18 ACS Paragon Plus Environment

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Figure 8: a) Bridge rectifier circuit and b) capacitor charging curves for 10 µF using NYG and 5NYCG PENG.

Conclusions Large area flexible nylon 11 and nylon 11/CNC composites films were prepared by a simple approach. Incorporation of a small quantity (2-5 wt%) of CNC and glycerol as plasticizer led to significant increase in polar γ-phase in nylon 11. This could be attributed to strong hydrogen bonding interactions between CNC and nylon 11 chains. The enhanced γ-phase crystallization also manifested in superior piezoelectric performance of nylon11/CNC composites. Energy harvesting devices fabricated from as prepared and corona poled films showed ~ 3 fold enhancement in output voltage for nylon11/CNC composites as compared to neat nylon 11. The piezoelectric performance was found to be reproducible even after 800 cycles of impact and three months of storage. When energy harvested from mechanical impact was used to charge a capacitor, nylon11/CNC composites led to 2.8 times higher voltage accumulation than nylon 11. The low cost, flexible and durable devices could have potential applications in self-powering sensors and powering of other small electronics.



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SUPPORTING INFORMATION Supporting Information is available from the journal or from the author. (Determination of carboxylic content of CNC; FTIR and TEM of CNC, Scheme for preparation of brittle films, Scheme for fabrication of nanogenerator and FTIR table to determine the phases of nylon 11 can be found in ESI.). AUTHOR INFORMATION Conflicts of interest: There are no conflicts to declare Corresponding Author Dr. Kadhiravan Shanmuganathan, Mail: [email protected], Polymer and Advanced Materials Laboratory, Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Pune. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ACKNOWLEDGMENT The authors wish to acknowledge Dr. Manjusha Shelke for allowing to use their oscilloscope facility, Mr. Vivek Borkar and Mr. Swapnil Aherrao for help with poling experiments. This work was facilitated by financial support from the Department of Science and Technology,


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Government of India (SB/S3/CE/014/2015) and University Grants Commission through Senior Research Fellowship for Mr. Farsa Ram. References:

(1) Lovinger, A. J. Ferroelectric Polymers. Science 1983, 220, 1115-1121. (2) Park, S.; Kim, Y.; Jung, H.; Park, J. Y.; Lee, N.; Seo, Y. Energy harvesting efficiency of piezoelectric polymer film with graphene and metal electrodes. Sci. Rep. 2017, 7, 17290. (3) Lee, S. J.; Arun, A. P.; Kim, K. J. Piezoelectric properties of electrospun poly (L-lactic acid) nanofiber web. Mater. Lett. 2015, 148, 58-62. (4) Csoka, L.; Hoeger, I. C.; Rojas, O. J.; Peszlen, I.; Pawlak, J. J.; Peralta, P. N. Piezoelectric effect of cellulose nanocrystals thin films. ACS Mater. Lett. 2012, 1, 867-870. (5) Wang, A. C.; Wu, C.; Pisignano, D.; Wang, Z. L.; Persano, L. Polymer nanogenerators: Opportunities and challenges for large‐scale applications. J. Appl. Polym. Sci. 2018, 135, 45674. (6) Lu, K.; Huang, W.; Guo, J.; Gong, T.; Wei, X.; Lu, B. W.; Liu, S. Y.; Yu, B. Ultra-sensitive strain sensor based on flexible poly (vinylidene fluoride) piezoelectric film. Nanoscale Res. Lett. 2018, 13, 83. (7) Sharma, T.; Aroom, K.; Naik, S.; Gill, B.; Zhang, J. X. Flexible thin-film PVDF-TrFE based pressure sensor for smart catheter applications. Ann. Biomed. Eng. 2013, 41,744–751. (8) Poncet, P.; Casset, F.; Latour, A.; Santos, F. D. D.; Pawlak, S.; Gwoziecki, R.; Devos, A.; Emery, P.; Fanget, S. Static and dynamic studies of electro-active polymer actuators and integration in a demonstrator. Actuators 2017, 6, 18. (9) Wang, Z.; Pan, X.; He, Y.; Hu, Y.; Gu, H.;Wang, Y. Piezoelectric nanowires in energy harvesting applications. Adv. Mater. Sci. Eng. 2015, 2015, 165631. 21 ACS Paragon Plus Environment


Page 22 of 26

(10) Li, Q.; Wang, Q. Ferroelectric polymers and their energy‐related applications. Macromol. Chem. Phys. 2016, 217, 1228-1244. (11) Meurisch, K.; Gojdka, B.; Strunskus, T.; Zaporojtchenko, V.; Faupel, F. Vapour phase deposition of highly crystalline self-poled piezoelectric nylon-11. J. Phys. D: Appl. Phys. 2012, 45, 055304. (12) Litt, M. H.; Hsu, C. H.; Basu, P. Pyroelectricity and piezoelectricity in Nylon 11. J. Appl. Phys. 1977, 48, 2208-2212. (13) Scheinbeim, J. I. Piezoelectricity in γ‐form Nylon 11. J. Appl. Phys. 1981, 52, 5939-5942. (14) J Scheinbeim, J. I.; Lee, J. W.; Newman, B. A. Ferroelectric Polarization Mechanisms in Nylon 11. Macromolecules 1992, 25, 3729-3732. (15) Tsutsumi, N.; Yamaoka, T. Ferroelectric properties of ultrathin films of Nylon 11. Thin Solid Films 2009, 518, 814–818. (16) Li, K.; Wang, H.; Ding, A. Polyamide-11/lead zirconate titanates-a novel composite material with high dielectric properties. Polymer Science, Ser. B 2010, 52, 438-442. (17) Capsal, J. F.; Dantras, E.; Laffont, L.; Dandurand, J.; Lacabanne, C. Nanotexture influence of BaTiO3 particles on piezoelectric behaviour of PA 11/BaTiO3 nanocomposites. J. Non-Cryst. Solids 2010, 356, 629-634. (18) Ravindran, R. E. S.; Thomas, P.; Renganathan, S. Effect on dielectric, structural and thermal behavior of CaCu3Ti4O12 in a Nylon 11 matrix. Bull. Mater. Sci. 2019, 42:28. (19) David, C.; Capsal, J. F.; Laffont, L.; Dantras, E.; Lacabanne, C. Piezoelectric properties of polyamide 11/NaNbO3 nanowire composites. J. Phys. D: Appl. Phys.2012, 45, 415305.


Page 23 of 26 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


(20) Huang, Y.; Tan, L.; Zheng, S.; Liu, Z.; Feng, J.; Yang, M. B. Enhanced dielectric properties of polyamide 11/multi‐walled carbon nanotubes composites. J. Appl. Polym. Sci. 2015, 132, 42642 . (21) Li, R.; Xiong, C.; Kuang, D.; Dong, L.; Lei, Y.; Yao, J.; Jiang, M.; Li, L. Polyamide 11/poly (vinylidene fluoride) blends as novel flexible materials for capacitors. Macromol. Rapid Commun. 2008, 29, 1449-1454. (22) Kuang, D.; Li, R.; Pei, J. Polyamide 11/poly (vinylidene fluoride)/vinyl acetate-maleic anhydride copolymer as novel blends flexible materials for capacitors. Polymers 2014, 6, 21462156. (23) Panaitescu, D. M.; Frone, A. N.; Nicolae, C. Micro-and nano-mechanical characterization of polyamide 11 and its composites containing cellulose nanofibers. Eur. Polym. J. 2013, 49, 38573866. (24) Panaitescu, D. M.; Gabor, R. A.; Frone, A. N.; Vasile, E. Influence of thermal treatment on mechanical and morphological characteristics of polyamide 11/cellulose nanofibers nanocomposites. J. Nanomater. 2015, 16, 4. (25) Rohner, S.; Humphry, J.; Chaléat, C. M.; Vandi, L. J.; Martin, D. J.; Amiralian, N.; Heitzmann, M. T. Mechanical properties of polyamide 11 reinforced with cellulose nanofibres from Triodia pungens. Cellulose 2018, 25, 2367-2380. (26) Datta, A.; Choi, Y.S.; Chalmers, E.; Ou, C.; Kar‐Narayan, S. Piezoelectric Nylon‐11 Nanowire Arrays Grown by Template Wetting for Vibrational Energy Harvesting Applications. Adv. Funct. Mater. 2017, 27, 1604262. (27) Paillet, M.; Dufresne, A. Chitin Whisker Reinforced Thermoplastic Nanocomposites. Macromolecules 2001, 34, 6527-6530. 23 ACS Paragon Plus Environment


Page 24 of 26

(28) Araki, J.; Wada, M.; Kuga, S. Steric stabilization of a cellulose microcrystal suspension by poly(ethylene glycol) grafting. Langmuir 2001, 17, 21-27. (29) Dhanalakshmi, M.; Jog, J. P. Preparation and characterization of electrospun fibers of Nylon: Express Polymer Lett. 2008, 2, 540–545. (30) Ram, F.; Ambone, T.; Sharma, A.; Murugesan, R.; Kajale, D.; Borkar, V.; Ali, S.F.; Balu, P.K.; Kumaraswamy, G.; Shanmuganathan, K. Fluorinated nanocellulose-reinforced all-organic flexible ferroelectric nanocomposites for energy generation. J. Phys. Chem. C 2018, 122, 1654016549. (31) Nair, S. S.; Ramesh, C.; Tashiro, K. Crystalline phases in nylon-11: studies using HTWAXS and HTFTIR. Macromolecules 2006, 39, 2841-2848. (32) Gogolewski, S. Effect of annealing on thermal properties and crystalline structure of polyamides. Nylon 11 (polyundecaneamide). Colloid. Polym. Sci. 1979, 257, 811-819. (33) Choi, Y. S.; Kim, S. K.; Williams, F.; Ellioat, J. A.; Kar‐Narayan, S. The effect of crystal structure on the electromechanical properties of piezoelectric Nylon-11 nanowires. Chem. Commun. 2018, 54, 6863-6866.

(34) Nair, S. S.; Ramesh, C.; Tashiro, K.; Polymorphism in Nylon‐11: Characterization using HTWAXS and HTFTIR. Macromolecular symposia 2016, 242, 216-226 (35) Garain, S.; Sinha, T. K.; Adhikary, P.; Henkel, K.; Sen, S.; Ram, S.; Sinha, C.; Schmeißer, 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, 12981307. (36) Liu, T.; Lim, K.;P.; Tjiu, W. C.; Pramoda, K. P.; Chen, Z. K. Preparation and characterization of nylon 11/organoclay nanocomposites. Polymer 2013, 44, 3529-3535.


Page 25 of 26 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


(37) Nguyen, M. D.; Houwman, E. P.; Rijnders, G. Large piezoelectric strain with ultra-low strain hysteresis in highly c-axis oriented Pb (Zr0.52Ti0.48)O3 films with columnar growth on amorphous glass substrates. Sci. Rep. 2017, 7, 12915. (38) Dhanalakshmi, M. Electrospinning of biocompatible and biodegradable polymers and their application in scaffold tissue engineering, Chapter 5: Nylon11/ZnO Electrospun Mats, 2015,pp 97-110. (39) Karan, S. K.; Mandal, D.; Khatua, B.B. Self-powered flexible Fe-doped RGO/PVDF nanocomposite: an excellent material for a piezoelectric energy harvester. Nanoscale 2015, 7, 10655-10666. (40) Li, Q.; Ke, W.; Chang, T.; Hu, Z. A molecular ferroelectrics induced electroactive β-phase in solution processed PVDF films for flexible piezoelectric sensors. J. Mater. Chem. C 2019, 7, 1532-1543 (41) Xue, J.; Wu, L.; Hu, N.; Qiu, J.; Chang, C.; Atobe, S.; Fukunaga, H.; Watanabe, T.; Liu, Y.; Ning, H.; Li, J. Evaluation of piezoelectric property of reduced graphene oxide (rGO)–poly (vinylidene fluoride) nanocomposites. Nanoscale 2012, 4, 7250-7255.

TOC graphic Highly Flexible Mechanical Energy Harvester Based on Nylon 11 Ferroelectric Nanocomposites Farsa Ram,1,2 Sithara Radhakrishnan,1 Tushar Ambone,1 Kadhiravan Shanmuganathan1,2*



1Polymer

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Science and Engineering Division, CSIR-National Chemical Laboratory, Dr. Homi

Bhabha Road, Pune, Maharashtra-411008 2Academy

of Scientific and Innovative Research, CSIR- National Chemical Laboratory, Dr.

Homi Bhabha Road, Pune, Maharashtra-411008


Highly Flexible Mechanical Energy Harvester Based on Nylon 11

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