Wormlike Acid-Doped Polyaniline: Controllable Electrical Properties

Subscriber access provided by UNIVERSITY OF LEEDS

Article

Wormlike Acid-Doped Polyaniline: Controllable Electrical Properties and Theoretical Investigation Yahong Zhang, Yuping Duan, Jia Liu, Guojia Ma, and Ming-liang Huang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b11617 • Publication Date (Web): 15 Jan 2018 Downloaded from http://pubs.acs.org on January 16, 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 free 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 accessible to all readers and 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.

The Journal of Physical Chemistry C 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 34 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 Journal of Physical Chemistry

Wormlike Acid-Doped Polyaniline: Controllable Electrical Properties and Theoretical Investigation †

†

†

‡

†*

Yahong Zhang , Yuping Duan ,∗, Jia Liu , Guojia Ma , Mingliang Huang †

Key Laboratory of Solidification Control and Digital Preparation Technology (Liaoning

Province), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116085, P.R. China ‡

Beijing Aeronautical Manufacturing Technology Research Institute, Beijing 100024, PR China

Abstract Polyaniline doped with hydrochloride acid was prepared via a chemical oxidative polymerization between APS oxidant and aniline monomer in hydrochloric acid solution with different concentrations. The diameter of each PANI wormlike nanorod is fairly uniform, and the diameter of PANI nanorod decreases with increase in concentration of HCl. For the degradation stage of the polymeric backbone, the rate of degradation increases with decrease in the HCl concentration, which means the sample synthesized in higher HCl concentration possess the more stable structures. The highest conductivity of 1.04 S/cm is achieved when HCl concentration is 1.0 mol/L, which generated uniformly branched knobbles with good dispersion and higher aspect ratio. The variation tendency of complex permittivity keeps coordinate with the conductivity. First-principles calculations verified that N(E) of PANIs in the protonated states are larger than that of the unprotonated PANI, which means that the conductivity is promoted by the interaction between PANI and doping hydrochloric

∗

Corresponding author.Tel: +8641184708446; fax: +86411 84708446

E-mail address: [email protected]; [email protected] 1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 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

acid through protonation. Furthermore, the N(E) of protonated PANIs increases as the ratio of protonic acid increases, which means that the increase of protonic acid ratio is conducive to the enhancement of the electronic conductivity of PANI. 1. Introduction Based on the description about the doping of polyacetylene and the discovery of remarkable electrical conduction in polymers,1 the organic polymers possessing the optical and electrical properties of the metals and retaining the attractive mechanical properties lead to various technological applications. The organic conducting polymers with extended π-conjugation along their chain backbone exhibit semiconducting behavior, and the electrical transport properties in the conductive polymers have been thoroughly studied.2-5 Due to the wide range of conductivity from the insulating to metallic regime, easy processibility, lower cost, and environmental stability, conjugated conducting polymers have become promising materials. Among the conducting polymers, polyaniline (PANI) has been regarded as the most potential conjugated polymer owing to its ease of preparation, high electrical conductivity, and controllable electrochemical and physical properties by protonation and oxidation. The presence of various of intrinsic redox states and the processability have made the PANI widely used in practical applications such as in electromagnetic interference (EMI) shielding,6 light-emitting diodes and chemical sensor devices.7, 8 The doped PANI with unique dielectric property and electrical conductivity should be an outstanding microwave absorbing material. On account of the simple and convenient operation, chemical oxidative polymerization is the commonly used method among the reported approaches for its preparation. The electrical conductivity is one of the most important parameters of π-electron conjugated PANI, which is directly influenced by dopant type, doping level, polymer chain size, and the synthesis 2


Page 2 of 34

Page 3 of 34 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


method,9-11and these parameters may change the molecular structures, consequently modify the electromagnetic properties of PANI. Recently, the electrical properties of conducting PANI have received considerable attention due to the important role in understanding of conducting mechanism and fabrication of the nano devices. The effect of additives on the conductivity properties of polyaniline nanofiber has been studied.12-14 The conductivity of the additives assisted PANI increased at first and then decreased with the increased additive dosage. The morphology property of PANI affected its conductivity significantly. The increased conductivity is ascribed to the increased molecular weight and the dramatic morphology change of PANI, while the decreased conductivity is considered to be due to the reduction of molecular weight. Oyharçabal et al. have investigated the conductivity property of epoxy-PANI composites.15-16 The electrical conductivity of all composites increased with the PANI content, and dramatic increase near the percolation threshold was found. At the same time, the electrical conductivity increases more slowly above the electrical percolation threshold. The ratios of DBSA to CTAB show significant influence on the conductivities of chiral PANI. The mixed surfactants have special effecton the PANI molecular orientation as well as the electron density of whole structure. The optimization of morphology and electrical conductivity of PANI can be acquired through the preferable control of CTAB-SDBS ratios.17-18 Zhang et al. have studied how the inorganic acids and the molar ratio of FeCl3 to aniline influence the conductivity of the PANI-HCl nanofibers. The low redox potential FeCl3 is an excellent oxidant to prepare nano-scaled PANI, and the highly crystalline and thinner PANI nanofibers with considerable conductivity can be prepared through the concentration regulation of [FeCl3]/[An] ratios during the self-assembly process.19-20 3



The

chemical

oxidative

polymerization

of

aniline

Page 4 of 34

with

ammonium

peroxydisulfate (APS) in acid medium is the typical method to prepare PANI. It has been reported that the morphology feature of PANI prepared by the oxidation extremely depends on the acidity of the reaction medium.21-25 The aim of the present work is to investigate the effects of HCl-doping concentration on the electrical properties of PANI. Furthermore, a detailed first-principles study was performed to investigate the polymer chains with different doping levels. The common features and differences in the oxidation of APS and aniline under various HCl concentrations are discussed with respect to the experimental findings, and how the doping levels affect both the chemical and electronic properties of PANI is summarized. 2. Experimental and theoretical details 2.1 Synthesis of doped PANI at different HCl concentrations All reagents were of analytical grade and used without further treatment. The synthesis of HCl doped polyaniline by chemical oxidative polymerization was conducted in aqueous solution with APS as oxidant. 6 mL aniline and 15.024 g APS were dissolved in 180 mL and 90 mL HCl solution of certain concentration (0.4 M, 0.6 M, 0.8M, 1.0 M, and 1.2 M) respectively. Then, the APS solution was dropwise added to the aniline solution with continuous electromagnetic stirring, and the resulting solution was under electromagnetic stirred for about half an hour. The mixture was maintained for polymerization at 15℃ for 24h. After the reaction was finished, the residue was collected in a Buchner funnel. The dark green product was washed distilled water and absolute ethyl alcohol for several times to remove the undesired soluble ions and finally dried in vacuum at 60℃ for 24 h. 2.2 Characterization techniques The morphology, shape and size of the HCl doped PANI were observed on a 4


Page 5 of 34 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


field emission scanning electron microscope (SEM, SUPRA55). The crystal structures of the PAN I were determined by X-ray powder diffraction (XRD, EMPYREAN) analyses with Cu Kα radiation, using an operating voltage and current of40.0 kV and 40.0 mA, respectively. The scanning range was from 5° to 50°, and the scan speed was 4.00°min-1.Thermal degradation properties of the PANI were studied by a thermogravimetric analysis (TGA, TGA/SDTA851e). All PANI samples were heated from 25 to 700 ℃ with a heating rate of 10 ℃/minandan air flow rate of 60 mL/min. Fourier transform infrared (FTIR, Bruker Vertex-70) spectra were observed from 4000 to 400 cm-1. 2.3 Electrical conductivity measurement The PANI samples were pressed in the form of disc pellets with a diameter of 13 mm under a pressure of 5 MPa for 1 min in a hydraulic presser and the average thickness was about 1 mm. The pellets were used to measure the electrical conductivity using a RTS-9 model four-point probe. 2.4 Microwave dielectric properties measurement The relative complex permittivity versus frequency was carried out by coaxial refection/transmission method using an Aglient 8722ES vector network analyzer in the frequency range of 2-18 GHz. A sample containing 30 wt % of obtained products was pressed into a toroidal-shaped mould with an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 2 mm for microwave measurement in which paraffin wax was used as the binder. 2.5 Theoretical calculations In this work, a detailed first-principles investigation was performed to explore how will protonic acid at the polymerchain aﬀect the electronic properties of PANI. For this purpose, PANIs doped with different ratio of hydrochloric acid are 5



investgated to provide insight into how their electronic properties depend on their doping degree. The CASTEP code of Materials Studio was used to optimize the structure of PANIs. The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) was used and the ultrasoft pseudopotential was used. A 2×2×2 Monkhorst-Pack grid in Brillouin zone and a 500 eV cutoff energy were chosen after testing. The convergence tolerance were set as: the total energy is converged to 5.0×10-6 eV per atom, the residual stress is less than 0.02 GPa and the residual force is less than 0.01 eV/Å. 3. Results and Discussion 3.1 Morphology and microstructure Typical morphologies of PANI samples synthesized under different HCl concentrations are recorded and compared in Fig. 1, and it can be observed from the SEM graphs that the diameter of each PANI wormlike nanorod is fairly uniform. The diameter of the PANI nanorods produced from the chemical oxidative polymerization is estimated in the range of 130-150 nm with several micrometers in length when the HCl concentration is 0.4-0.6 mol/L. Their surfaces are not smooth and contain some microstructures. When the solution concentration increased to 0.8-1.0 mol/L, the diameter of PANI further decreases to 120 ± 10nm. The wormlike structures of PANI still exhibit rough and uniform surfaces, and the micro knobbles on the surface are decrescent with the increased HCl concentration. The smooth surface of PANI is obtained in 1.2 mol/L HCl solution, and the diameter is much thinner (about 80 nm in diameter). The result indicates that the concentration of HCl solution is found to strongly affect the morphology of PANI. In other words, the diameter of PANI nanorods decreases with increase in concentration of HCl, and the aspect ratio of 1D structure increased with the increasing HCl concentration. So, the concentrations of 6


Page 6 of 34

Page 7 of 34 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


HCl seem to be responsible for the changes in the morphology of the PANI.

Figure 1. SEM images of the PANIs synthesized in different HCl concentrations. The concentration of hydrochloric acid is labeled on the top right corner of each image, and the unit of the concentration is mol/L. The diameter of each PANI wormlike nanorod is fairly uniform, and the diameter of PANI nanorod decreases withincrease in concentration of HCl.

The powder XRD patterns of PANI samples are shown in Fig. 2. It is obvious, with an increasing concentration of HCl, the peak positions of PANIs prepared indifferent solution concentrations are almost the same. The characteristic diffraction 7



peaks are labeled, and these peaks display the amorphous feature of typical PANI emeraldine salt form. 9,13,26-27The diffraction peak observed at 15.3° is ascribed to the characteristic repeating units and doping diffraction peak of PANI, and the two peaks at 20.4°/25.3°are corresponding to the (020) and (200) reflection planes parallel and perpendicular to the PANI chains, respectively.26,28-32 The two intense peaks at 2θ=20.4° and 25.3°are sharper and stronger, and this may be due to the appearance of a relatively ordered structure of the polymer chain.33-34 It can be noted that as the concentration of HCl increases, the peak intensity of the PANI powders first increase and then decrease. When the concentration is increased to 1.2mol/L, the sample shows the weakest peak intensity, which means that the too high HCl concentration is inconducive to synthesize PANI with high degree of crystallinity. It is well known that the electrical conductivity of polymer improves with the increased crystallinity and doping degree.

Figure 2. The XRD patterns of the PANIs synthesized in different HCl concentrations. 8


Page 8 of 34

Page 9 of 34 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 peak positions of PANIs prepared in different solution concentrations are almost the same.

Fig. 3 shows the TGA curves of the PANI structures prepared in different HCl concentrations. The TGA plots show that weight loss occurs in three systematic stages each corresponds to the loss of particular species, and there are always some overlaps in weight loss ranges without sharp transitions between different stages. The first loss stage from room temperature to 110 ◦C may be attributed to the release of the sorbed water molecules and the residue organic solvent entangled in the polymer chains. The second loss step between 110 and 270◦C involves the loss of the doping acid in the form of HCl gas.26,27,35 The final loss step (270-700 ◦C) involves the heavier fragments into still smaller fractions and gaseous by products as well as the breakdown of polymeric backbone. As evident from the TGA curves, the increasing concentration of HCl does not have much influence on the decomposition temperature of PANI structures. It is obvious that the second loss step of the sample synthesized in 0.4 mol/L HCl shows the largest weight loss, which mean more acids should be removed from the polymer chains. For the degradation stage of the polymeric backbone, the rate of degradation increases with decrease in the HCl concentration, which means the sample synthesized in higher HCl concentration possess the more stable structures.

9



Figure 3. TGA analysis of the PANIs synthesized in different HCl concentrations. TheTGA plots show that weightloss occurs in three systematic stages each corresponds to the loss of particular species: release of the sorbed water molecules and the residue organic solvent, loss of the doping acid in the form of HCl gas, breakdown of polymeric backbone.

The FTIR spectra of the PANI prepared in different HC concentrations are shown in Fig. 4. As one can see, FTIR spectra of the PANI are quite similar and in good agreement with the previously reported results, which suggests that the effect of the HCl concentration on the main chain structures of PANI can be neglected.36-39 The strong absorption peaks at 1572 and 1485 cm-1 are correspond to the C=C stretching vibration of the quinoid and benzenoid rings, respectively.40-42 The peak at 1299 cm-1 is related to the C-N stretching vibration of secondary aromatic amine. The peak at 1121 cm-1 is assigned to the aromatic C-H in-plane bending. The peak at 801 cm-1 is due to the out-of plane bending of C-H in the substituted benzenoid ring. Measurement on FTIR indicates that the nanofibers are identical to the emeraldine salt 10


Page 10 of 34

Page 11 of 34 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


form of PANI, i.e., the conducting state. This agrees with the results obtained from the conductivity measurements by the four-probe method.

Figure 4. FT-IR spectra of the PANIs synthesized in different HCl concentrations. The FTIR spectra of the PANIs are quite similar, which suggests that the effect of the HCl concentrationon the main chain structures of PANI can be neglected. The insert figure is the intensity ratio of absorption peaks at 1572 and 1485 cm-1.

3.2 Electrical conductivity The intensive study of conductivity of the synthesized polymer is shown in Fig. 5. It is observed that the conductivities of PANI are related to different concentrations of HCl solution. In the range from 0.4-1.0 mol/L, the conductivities of PANI show the improving tendency with the increasing of concentration. When the concentration is increased to 1.0 mol/L, the highest conductivity of 1.04 S/cm is achieved, which 11



generated uniformly branched knobbles with good dispersion and higher aspect ratio. Nevertheless, the further increasing of the HCl concentration will lead to the decrease of the conductivity. It has been recently observed that the conductivity is affected by the size of conducting polymers, in other words, the decrease of diameter will increase the conductivity of the polymer, which is consistent with Martin’s suggestion.43 The increased conductivity from 0.4-1.0 mol/L may due to the decreased diameter of PANI. The morphology could affect the electrical conductivity of π-conjugation polymer from respects of arrangement of PANI molecular chains and density of electrons.17,44-46 The improved electrical conductivity maybe due to the high density of electrons as a result of dense knobbles throughout polymer chains. The electrons move throughout the length of PANI wormlike nanorods then further extend to the branched knobbles, resulting in the increase of charge delocalization, which is beneficial to the enhancement of electrical conductivity. The relatively lower conductivity is observed when the HCl concentration is increased to 1.2 mol/L. It is easy to see that the sample synthetized in 1.2 mol/L HCl shows the smooth surface, which means that the smooth surface is not beneficial to charge delocalization compared with the rough surface.17 The spectra of PANI show an diverse intensity ratio of 1580/1480 cm−1, which reveals that the ratio of quinoid/benzoid is different in each PANI.47-48 The calculated I1572/I1485 values of PANIs with different HCl concentrations are plotted in Fig. 5. It is interesting that the variation tendency of I1572/I1485 is quite similar with the conductivity curve. Doping level is one of important factors affecting the electrical conductivity of PANI. The mechanism of protonation of the emeraldine base on the grounds of theoretical studies has been proposed by Stafström and coworkers originally.49 Heeger further discussed the doping mechanism and described as follow 12


Page 12 of 34

Page 13 of 34 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


three steps: reaction with protonic acid adds 2H+ to the nitrogens obtaining the bipolaron (ES1) form; internal redox reaction achieves the charged the polarons (ES2) form; polarons separation yields the final polaron (ES3) form.50 The bond length alternations (BLA) of the PANI structures involved in the doping mechanism, i.e., emeraldine base (EB), bipolaron form (ES1, ES2) and polaronic form (ES3) have been inserted in Fig. 5. BLA of the rings was calculated as the difference between the averaged values of longer and shorter C–C bonds in the rings. BLA for the N-containing fragments is determined as the difference between the lengths of the C-N bonds of the two carbons attached to the nitrogen. The proton-doping of EB reveals the tendency to reduce the quinoid character of the protonated ring (ring2) with decreased BLA, and the protonated quinoid ring tends to benzoid characters. The intensity ratio I1572/I1485 of samples decreased firstly then increased with increasing concentration, which means that the doping level is increased with increasing HCl concentration before 1.0 mol/L. The minimum I1572/I1485 appears at 1.0 mol/L, which should be responsible to the highest conductivity. The I1572/I1485 increased and the conductivity decreased at 1.2 mol/L, and the reason may be due to the too high HCl concentration which is not propitious to achieve the long conjugation structure.

13



Figure 5. (a) Room temperature conductivity of PANIs synthesized in different HCl concentrations. The intensity ratios of absorption peaks at 1572 and 1485 cm-1 are plotted for comparison. The conductivities of PANI are related to different concentrations of HCl solution. The conductivity increases first and then decreases. (b) The bond length alternations (BLA) of the PANI structures involved in the doping mechanism

3.3 Microwave dielectric property Microwave absorption properties of an absorber are mainly determined by its complex permittivity ( ε r = ε '− jε '' ) and complex permeability ( µ r = µ '− j µ '' ), where the real parts ( ε ' and µ ' ) and imaginary parts ( ε '' and µ '' ) stand for the two ways in which the electromagnetic field interact with materials: energy storage and energy loss of electric and magnetic energy.51-53 Many potential applications of an absorber are based on the performances at microwave frequency, so the frequency 14


Page 14 of 34

Page 15 of 34 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


response of relative complex permittivity of PANI is studied in this paper. Fig. 6 shows the complex permittivity of PANI in the range of 2-18 GHz. As is well known, PANI is usually taken as a kind of dielectric loss material with ideal complex permittivity. It is observed that both ε ' and ε '' of PANIs are obviously enhanced with the increase of HCl concentration before 1.0 mol/L. When the concentration of HCl solution is further increased to 1.2 mol/L, both ε ' and ε '' are decreased. By comparing the dielectric permittivity and the evaluated conductivity, it is not difficult to find that the variation tendency of dielectric permittivity with HCl concentration is in line with that of electrical conductivity, furthermore, the relationship between the complex permittivity and the conductivity at a specific frequency is shown in Fig. 7. The conductivity is considered to be one factor influencing the complex permittivity to a certain degree. According to the free electron theory,54 the PANI has a higher conductivity is favorable to enhance the complex permittivity. In addition, the uniform change tend can be seen that both ε ' and ε '' of all PANIs decrease gradually with the increase of frequency, and the samples display typical dielectric dispersion which is another important factor influencing the complex permittivity.55 The dipole relaxation polarization is the main contribution to the complex permittivity at microwave frequency. When an external electromagnetic field acts on the PANIs, dipoles will reorient themselves to parallel to the electromagnetic field, resulting in dipole polarization, and the reorient process will give rise to energy loss to overcome the electromagnetic field resistance. However, with the increase of electromagnetic frequency, the dipoles rearrangement cannot keep pace with the electromagnetic field. As a result, the dielectric response tends toward decreasing gradually. The inset figures show the decline of ε ' and ε '' , and the different value between the maximum at 2 GHz and the minimum at 18 GHz is calculated in the inset figure. It is obvious 15



that the ε ' and ε '' of PANI synthetized in 1.0 mol/L show the most distinct dielectric response characteristics than the other PANIs. Moreover, it can be found that both the real and imaginary parts of the relative complex permeability for all PANIs are approximate constants around 1.00 and 0.00, which means that the PANIs are unable to generate magnetic loss, so the curves of the real and imaginary parts are not shows in this work.

Figure 6. The complex permittivity of PANIs synthesized in different HCl concentration: (a) real parts and and (b) imaginary part. Both real parts and imaginary parts of PANIs are obviously enhanced with the increase of HCl concentration before 1.0 mol/L, and the samples display typical dielectric dispersion. In the inset figures, 16


Page 16 of 34

Page 17 of 34 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


Max-2GHz, Max-18GHz and D-value are the maximum value at 2GHz, minimum value at 18 GHz and the difference value between Max-2GHz and minimum value, respectively.

Figure 7. The relationship between complex permittivity (real part and imaginary part) and the conductivity at specific frequencies. The Debye formula is imported to further understand the dielectric response of the PANIs, and the complex permittivity can be represented as follows:56

ε ' = ε∞ + ε '' =

εs − ε∞ (1) 1 + ω 2τ 2

(ε s − ε ∞ ) ωτ 1 + ω 2τ 2

(2)

Where ε ∞ ( ε ∞ = limω →∞ ε r ) is the ultimate permittivity at infinite frequency, ε s ( ε s = limω →0 ε r ) is the permittivity at static frequency, ω and τ are the angular frequency and relaxation time, respectively. The deduced quation from Eqs. (1) and (2) can be obtained:

ε '=

ε '' + ε ∞ (3) 2π f τ

The relationship between ε ' and ε ''/ f of the PANIs is shown in Fig. 8(a), and the fit lines are obtained with the assistance of linear regression analysis. As 17



shown in Fig. 8(a), there are three linear functions with different slopes for the curves of all PANIs, and all the slopes of each curve are calculated in Fig. 8(b). Furthermore, the corresponding relaxation times can be speculated from the slopes of the line ( k = 1/ 2πτ ). It indicates that the relaxation times for the second and third stages are longer than the first stage in each corresponding fit line, which means that the dipoles will need more time to reorient their directions at the external electromagnetic field.

Figure 8 (a) The plots of ε ' versus ε ''/ f for the PANIs synthesized in different HCl concentration. The plots deviate from a single linear function due to the coexistence of several polarization processes. (b) The slopes of each curve calculated according to the fit lines in (a). The unit of the hydrochloric acid concentration is mol/L.

Based on the above discussions on complex permittivity, dielectric conductivity is another significant parameter evaluating the responses of a microwave absorber to the external electromagnetic field. In particular, dielectric conductivity is a 18


Page 18 of 34

Page 19 of 34 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


comprehensive parameter taking into consideration various dissipative effects: not only the conductivity aroused by charge carriers but also the energy loss caused by the dipole polarization. The dielectric conductivity of synthesized PANIs is calculated from Eq. 5 ( ε 0 =8.854 × 10-12 F / m is the permittivity of free space) and shown in Fig. 9.57

σ =ωε 0ε '' (4) The obvious tendency can be found that the dielectric conductivity of PANIs increases with the increasing frequency. In addition, the impacts of the concentration of hydrochloric acid are non-negligible. Within a given range of concentration (0.4-1.0 mol/L), the increase in HCl concentration is helpful to the enhancement of the dielectric conductivity, and the highest conductivity on the specific frequency is achievedin 1.0 mol/L HCl solution. The increase in HCl concentration will arouse the improvement of doping level of PANI which will increase the concentration of charge carriers and further enlarge the dielectric conductivity of PANI.

Figure 9 The dielectric conductivity versus frequency for the PANIs synthesized in different HCl concentration. The dielectric conductivity of PANIs increases with the 19



increasing frequency, and the increase in HCl concentration is helpful to the enhancement of the dielectric conductivity before 1.0 mol/L.

3.4 First-principles calculations To obtain deeper insight into the electronic properties of the polymer structures, the electrostatic potential (ESP) of the unprotonated and HCl-protonated PANIs are compared, respectively. Moreover, to determine whether the electrical conductivity of the doped PANIs has been changed, the density of states at the Fermi level N(E) of the doped PANIs (ES-2HCl and ES-4HCl) as well as the emeraldine base (EB) form of PANI are calculated. The finite molecular models for the unprotonated emeraldine base form of PANI (EB) and the protonated emeraldine salts form of PANI with different ratio of protonic acidare represented in Fig. 10, respectively.

Figure 10 The fnite molecular models for the unprotonated emeraldine base (EB) form of PANI as well as HCl-protonated PANIs (ES-2HCl and ES-4HCl). The hydrogen, carbon, nitrogen and chlorine atoms are shown in white, grey, blue and green, respectively. 20


Page 20 of 34

Page 21 of 34 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 arrangements of molecular solid-state could be sensitive to various intermolecular interactions, and strongly influence the charge transport behavior. The electrostatic potential (ESP) could be used to analyze the non-covalent interactions.58-61 Fig. 11 shows the electrostatic potential (ESP) isosurfaces of the investigated PANIs in the unprotonated and protonated states. The visible results show that for the unprotonated emeraldine base state, the electrostatic potentials the positive and negative areas are uniformly located on the skeleton of the π-conjugated PANI. The positive areas are mainly spread over the hydrogen atoms, and negative areas are mainly distributed on the nitrogen atoms. However, the electrostatic potentials on the conjugated ES-2HCl and ES-4HCl turn out to be unbalanced due to the introduced protonic acid. The most negative areas are concentrated on the coanion. It has been demonstrated that the electrostatic potential can be regarded as a fundamental factor in determining the natures and behavior of atoms and molecules.62 The novel method has been proposed to define dynamical electrostatic potential derived charges for systems.63,64 Based on the assumption that the area of the hole and electron puddles is equal in size and simplify the spatial electrostatic potential to a step function, the total carrier density at the Dirac point is related the electrostatic potential.65 The unbalanced electrostatic potential isosurfaces of emeraldine salts could be beneficial to the charge transport behavior of PANI.

21



Page 22 of 34

Figure 11 The molecular surface electrostatic potentials of EB, ES-2HCl and ES-4HCl (scale bar: |e| in atomic unit)

The adjustable electronic conductivity accompanying with the doping/dedoping process makes PANI hold a special position among conductive polymers. Based on the Mott’s variable-range hopping mechanism,66-68 the electronic conductivity of PANI can be presented as:69-70 ⁄

9 8

⁄

(5)

where σ is the conductivity, N(E) is the density of states (DOS) at Fermi level, e is the electronic charge, is the jump rat factor, 18.1 is a dimensionless constant,68 is the inverse rate of fall of the wave function,67 T is the temperature (298 K in our calculation) and kB is the Boltzmann constant. At a certain temperature, the electronic conductivity of the organic polymers is related to the density of states at the Fermi energy. Whether the conductivity of PANIs will be changed by the presence of protonic acid is interesting question to pursue.

22


Page 23 of 34 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


Hence, to obtain deeper insight into the conductivity character of PANIs, the density of states of EB, ES-2HCl and ES-4HCl are calculated and compared in Fig.12. The vertical dashed line represents the position of N(E), and the calculated density of state of EB is in agreement with previous studies.69,70 Comparing N(E) values of the PANIs in the protonated and unprotonated states, it is clear that the N(E) of PANIs in the protonated states are larger than that of the unprotonated PANI, which means that the conductivity is promoted by the interaction between PANI and doping hydrochloric acid through protonation. Additionally, the N(E) of protonated PANIs increases as the ratio of protonic acid increases, which means that the increase of protonic acid ratio is conducive to the enhancement of the electronic conductivity of PANI.

Figure 12 Density of states of EB, ES-2HCl and ES-4HCl according to periodic molecular models. The vertical dashed lines represent the Fermi level.

4. Conclusions The HCl doped PANI was prepared via chemical oxidative polymerization of aniline monomer. The diameter of each PANI wormlike structure is fairly uniform, 23



Page 24 of 34

and the diameter of PANI nanorod decreases with increase in concentration of HCl. Doping did not change the crystal phase or the one-dimensional morphology. The PANIs synthesized in higher HCl concentration possess the more stable structures. The electrical conductivity increases first and then decreases, and the highest conductivity of 1.04 S/cm is achieved when HCl concentration is 1.0 mol/L. The variation tendency of complex permittivity keeps coordinate with the conductivity, and the higher conductivity is favorable to enhance the complex permittivity. First-principles calculations verified that the conductivity is promoted by the interaction between PANI and doping hydrochloric acid through protonation, in addition, the increase of protonic acid ratio is conducive to the enhancement of the electronic conductivity of PANI.

Acknowledgements

The authors acknowledge the Supported by Program for the National Key R&D Program of China (2017YFB0703103), the National Natural Science Foundation of China (No. 51577021), and the Fundamental Research Funds for the Central Universities (DUT17GF107), and the Industry-University-Research Collaboration Project of Aviation Industry Corporation of China (cxy2103DLLG34).

References (1) Chiang, C. K.; Fincher Jr C. R.; Park, Y. W.; Heeger, A. J.; Shirakawa, H.; Louis, E. J.; Gau, S. C.; MacDiarmid, A. G. Electrical Conductivity in Doped Polyacetylene.

Phys. Rev. Lett. 1977, 39, 1098-1101. (2)

Reiss,

P.;

Couderc,

E.;

Girolamo,

De

J.;

Pron,

A.

Conjugated

Polymers/Semiconductor Nanocrystals Hybrid Materials-Preparation, Electrical Transport Properties and Applications. Nanoscale 2011, 3, 446-489. (3) Kreuer, K. D. On the Development of Proton Conducting Polymer Membranes for 24


Page 25 of 34 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


Hydrogen and Methanol Fuel Cells. J. Membrane Sci. 2001, 185, 29-39. (4) Kang, K.; Watanabe, S.; Broch, K.; Sepe, A.; Brown, A.; Nasrallah, I.; Nikolka, M.; Fei, Z.; Heeney, M.; Matsumoto, D. et al. 2D Coherent Charge Transport in Highly Ordered Conducting Polymers Doped by Solid State Diffusion. Nat. Mater.

2016, 15, 896-902. (5) Rivnay, J.; Inal, S.; Collins, B. A.; Sessolo, M.; Stavrinidou, E.; Strakosas, X.; Tassone C.; Delongchamp, D. M.;

Malliaras, G. G. Structural Control of Mixed

Ionic and Electronic Transport in Conducting Polymers. Nat. Commun. 2016, 7, 11287. (6) Bora, P. J.; Vinoy, K. J.; Ramamurthy, P. C.; Madras, G. Electromagnetic Interference Shielding Efficiency of MnO2 Nanorod Doped Polyaniline Film. Mater.

Res. Express 2017, 4, 025013. (7) Mohsennia, M.; Bidgoli, M. M.; Boroumand, F. A.; MohsenNia, A. Electrically Conductive Polyaniline as Hole-Injection Layer for MEH-PPV: BT Based Polymer Light Emitting Diodes. Mater. Sci. Eng. B 2015, 197, 25-30. (8) Bai, S.; Sun, C.; Wan, P.; Wang, C.; Luo, R.; Li, Y.; Liu, J.; Sun, X. Transparent Conducting Films of Hierarchically Nanostructured Polyaniline Networks on Flexible Substrates for High-Performance Gas Sensors. Small 2015, 11, 306-310. (9) Chaudhari, H. K.; Kelkar, D. S. Investigation of Structure and Electrical Conductivity in Doped Polyaniline. Polym. Int. 1997, 42, 380-384. (10) McManus, P. M.; Cushman, R. J.; Yang, S. C. Influence of Oxidation and Protonation on the Electrical Conductivity of Polyaniline. J. Phys. Chem. 1987, 91, 744-747. (11) Yue, J.; Epstein, A. J. Synthesis of Self-Doped Conducting Polyaniline. J. Am.

Chem. Soc. 1990, 112, 2800-2801. 25



(12) Prokeš, J.; Křivka, I.; Stejskal, J. Control of Electrical Properties of Polyaniline.

Polym. Int. 1997, 43, 117-125. (13) Zhao, Y.; Arowo, M.; Wu, W.; Chen, J. Effect of Additives on the Properties of Polyaniline Nanofibers Prepared by High Gravity Chemical Oxidative Polymerization.

Langmuir 2015, 31, 5155-5163. (14) Prokes, J.; Stejskal, J.; Krivka, I.; Tobolkova, E. Aniline-Phenylenediamine Copolymers. Synth. Met. 1999, 102, 1205-1206. (15) Oyharçabal, M.; Olinga, T.; Foulc, M. P.; Vigneras, V. Polyaniline/clay as Nanostructured Conductive Filler for Electrically Conductive Epoxy Composites. Influence of Filler Morphology, Chemical Nature of Reagents, and Curing Conditions on Composite Conductivity. Synth. Met. 2012, 162, 555-562. (16) Oyharçabal, M.; Olinga, T.; Foulc, M. P.; Lacomme, S.; Gontier E.; Vigneras, V. Influence of the Morphology of Polyaniline on the Microwave Absorption Properties of Epoxy Polyaniline Composites. Compos. Sci. Technol. 2013, 74, 107-112. (17) Zhou, D.; Li, Y.; Wang, J.; Xu, P.; Han, X. Synthesis of Polyaniline Nanofibers with High Electrical Conductivity from CTAB-SDBS Mixed Surfactants. Mater. Lett.

2011, 65, 3601-3604. (18) Guo, H.; Chen, J.; Xu, Y. Hb-Induced Biocatalyzed Synthesis of Water-Soluble Polyaniline Nanocomposites with Controlled Handedness in DBSA-CTAB Mixed Micelle Solutions. Synth. Met. 2015, 205, 169-174. (19) Yasuda, A.; Shimidzu, T. Chemical and Electrochemical Analyses of Polyaniline Prepared with FeCl3. Synth. Met. 1993, 61, 239-245. (20) Zhang, Z.; Deng, J.; Wan, M. Highly Crystalline and Thin Polyaniline Nanofibers Oxidized by Ferric Chloride. Mater. Chem. Phys. 2009, 115, 275-279. (21) Zhang, Z.; Wei, Z.; Wan, M. Nanostructures of Polyaniline Doped with Inorganic 26


Page 26 of 34

Page 27 of 34 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


Acids. Macromolecules 2002, 35, 5937-5942. (22) Zhang, L.; Wan, M. Self‐Assembly of Polyaniline-From Nanotubes to Hollow Microspheres. Adv. Funct. Mater. 2003, 13, 815-820. (23) Gemeay, A. H.; Mansour, I. A.; El-Sharkawy, R. G.; Zaki, A. B. Preparation and Characterization of Polyaniline/Manganese Dioxide Composites via Oxidative Polymerization: Effect of Acids. Eur. Polym. J. 2005, 41, 2575-2583. (24) Venancio, E. C.; Wang, P. C.; MacDiarmid, A. G. The Azanes: A Class of Material Incorporating Nano/micro Self-Assembled Hollow Spheres Obtained by Aqueous Oxidative Polymerization of Aniline. Synth. Met. 2006, 156, 357-369. (25) Li, J.; Tang, X.; Li, H.; Yan, Y.; Zhang, Q. Synthesis and Thermoelectric Properties of Hydrochloric Acid-Doped Polyaniline. Synth. Met. 2010, 160, 1153-1158. (26) Jia, R.; Wu, Y.; Zan, G.; Liu, D. Synthesis and Characterization of Nanotree-Like Polyaniline Electrode Material for Supercapacitors. J. Mater. Sci.-Mater. Electron.

2017, 28, 2366-2376. (27) Saini, P.; Choudhary, V.; Singh, B. P.; Mathur, R. B.; Dhawan, S. K. Polyaniline-MWCNT Nanocomposites for Microwave Absorption and EMI Shielding.

Mater. Chem. Phys. 2009, 113, 919-926. (28) Dong, J. Q.; Shen, Q. Enhancement in Solubility and Conductivity of Polyaniline with Lignosulfonate Modified Carbon Nanotube. J. Polym. Sci., Part B: Polym. Phys.

2009, 47, 2036-2046. (29) Gu, Z. J.; Wang, J. T.; Li, L. L.; Chen, L. F.; Shen, Q. Formation of Polyaniline Nanotubes with Different Pore Shapes Using α-, β-and γ-cyclodextrins as Templates.

Mater. Lett. 2014, 117, 66-68. (30) Miao, Y. E.; Fan, W.; Chen, D.; Liu, T. X. High-Performance Supercapacitors 27



Page 28 of 34

Based on Hollow Polyaniline Nanofibers by Electrospinning. ACS Appl. Mater. Inter.

2013, 5, 4423-4428. (31) Gu, Z. J.; Ye, J. R.; Song, W.; Shen, Q. Synthesis of Polyaniline Nanotubes with Controlled Rectangular or Square Pore Shape. Mater. Lett. 2014, 121, 12-14. (32) Yan, Q.; Wang, M. Y.; Wu, Y. H.; Shen, Q. Tea Polyphenol as Environmentally Friendly Dopant and Thermal Stabilizer for Polyaniline. Mater. Lett. 2016, 170, 202-204. (33) Chen, W.; Rakhi, R. B.; Alshareef, H. N. Morphology-Dependent Enhancement of the Pseudocapacitance of Template-Guided Tunable Polyaniline Nanostructures. J.

Phys. Chem. C 2013, 117, 15009-15019. (34) Łużny, W.; Bańka, E. Relations between the Structure and Electric Conductivity of Polyaniline Protonated with Camphorsulfonic Acid. Macromolecules 2000, 33, 425-429. (35)

Palaniappan,

S.;

Narayana,

B.

H.

Conducting

Polyaniline

Salts:

Thermogravimetric and Differential Thermal Analysis. Thermochim. Acta 1994, 237, 91-97. (36) Srinivasan, S.; Pramanik, P. Optical Properties of Chemically Prepared Polyemeraldine. Synth. Met. 1994, 63, 199-204. (37) Wen, L.; Kocherginsky, N. M. Doping-Dependent Ion Selectivity of Polyaniline Membranes. Synth. Met. 1999, 106, 19-27. (38) Sapurina, I.; Mokeev, M.; Lavrentev, V.; Zgonnik, V.; Trchova, M.; Hlavata, D.; Stejskal, J. Polyaniline Complex with Fullerene C 60. Eur. Polym. J. 2000, 36, 2321-2326. (39) Kim, S. G.; Kim, J. W.; Choi, H. J.; Suh, M. S.; Shin, M. J.; Jhon, M. S. Synthesis

and

Electrorheological

Characterization 28


of

Emulsion-Polymerized

Page 29 of 34 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


Dodecylbenzenesulfonic Acid Doped Polyaniline-Based Suspensions. Colloid Polym.

Sci. 2000, 278, 894-898. (40) Quillard, S.; Louarn, G.; Lefrant, S.; Macdiarmid, A. G. Vibrational Analysis of Polyaniline:

A Comparative

Study

of

Leucoemeraldine,

Emeraldine,

and

Pernigraniline Bases. Phys. Rev. B 1994, 50, 12496. (41) Zhu, J.; Wei, S.; Zhang, L.; Mao, Y.; Ryu, J.; Karki, A. B. Polyaniline-Tungsten Oxide Metacomposites with Tunable Electronic Properties. J. Mater. Chem. 2011, 21, 342-348. (42) Furukawa. Y.; Ueda, F.; Hyodo, Y.; Harada, I.; Nakajima, T.; Kawagoe, T. Vibrational Spectra and Structure of Polyaniline. Macromolecules 1988, 21, 1297-1305. (43) Cai, Z.; Lei, J.; Liang, W.; Menon, V.; Martin, C. R. Molecular and Supermolecular Origins of Enhanced Electric Conductivity in Template-Synthesized Polyheterocyclic Fibrils. 1. Supermolecular Effects. Chem. Mater. 1991, 3, 960-967. (44) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. About Supramolecular Assemblies of π-conjugated Systems. Chem. Rev. 2005, 105, 1491-1546. (45) Martin, C. R. Nanomaterials: a Membrane-Based Synthetic Approach. Science

1994, 266, 1961-1966. (46) Zhang, Z.; Deng, J.; Yu, L.; Wan, M. Chrysanthemum Flower-Like Constructed Polyaniline Nanofibers Synthesized by Adding Inorganic Salts as Additives. Synth.

Met. 2008, 158, 712-716. (47) Yu, Y.; Che, B.; Si, Z.; Li，L.; Chen，W.; Xue, G. Carbon Nanotube/polyaniline Core-shell Nanowires Prepared by in Situ Inverse Microemulsion. Synth. Met. 2005, 150, 271-277. 29



(48) Zhao, Y.; Wu, W.; Chen, J.;

Page 30 of 34

Zou, H.; Hu, L.; Chu, G. Preparation of

Polyaniline/Multiwalled Carbon Nanotubes Nanocomposites by High Gravity Chemical Oxidative Polymerization. Industrial & Engineering Chemistry Research,

2012, 51, 3811-3818. (49) Stafström, S.; Bredas, J. L.; Epstein, A. J.; Woo, H. S.; Tanner, D. B.; Huang W. S.; MacDiarmid, A. G. Polaron Lattice in Highly Conducting Polyaniline: Theoretical and Optical Studies. Phys. Rev. Lett. 1987, 59, 1464-1467. (50) Heeger, A. J. Semiconducting and Metallic Polymers: The Fourth Generation of Polymeric Materials. J. Phys. Chem. B 2001, 105, 8475-8491. (51) Du, Y.; Liu, W.; Qiang, R.; Wang, Y.; Han, X.; Ma, J.; Xu, P. Shell Thickness-Dependent Microwave Absorption of Core-Shell Fe3O4@C Composites.

ACS Appl. Mater. Inter. 2014, 6, 12997-13006. (52) Duan, Y.; Liu, Z.; Jing, H.; Zhang, Y.; Li, S. Novel Microwave Dielectric Response of Ni/Co-doped Manganese Dioxides and Their Microwave Absorbing Properties. J. Mater. Chem. 2012, 22, 18291-18299. (53) Zhang, P.; Han, X.; Kang, L.; Qiang, R.; Liu, W.; Du, Y. Synthesis and Characterization of Polyaniline Nanoparticles with Enhanced Microwave Absorption.

RSC Adv. 2013, 3, 12694-12701. (54) Zhang, X.; Dong, X.; Huang, H.; Liu, Y.; Wang, W.; Zhu, X.; Lv, B.; Lei, J.; Lee, C. Microwave Absorption Properties of the Carbon Coated Nickel Nanocapsules.

Appl. Phys. Lett. 2006, 89, 053115. (55) Ohlan, A.; Singh, K.; Chandra, A.; Dhawan, S. K. Microwave Absorption Behavior of Core-Shell Structured Poly (3, 4-Ethylenedioxy Thiophene)-Barium Ferrite Nanocomposites. ACS Appl. Mater. Inter. 2010, 2, 927-933. (56)

Moliton,

A.

Applied

Electromagnetism

and

30


Materials;

Springer

Page 31 of 34 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


Science+Business Media: New York, 2007. (57) Chen, L. F.; Ong, C. K.; Neo, C. P.; Varadan, V. V.; Varadan, V. K. Microwave

Electronics: Measurement and Materials Characterization; John Wiley & Sons: England, 2004. (58)

Politzer,

P.;

Murray,

J.

S.;

Clark,

T.

Halogen

Bonding:

An

Electrostatically-Driven Highly Directional Noncovalent Interaction. Phys. Chem.

Chem. Phys. 2010, 12, 7748-7757. (59) Lee, H.; Yi, Y.; Cho, S. W.; Choi, W. K. Theoretical Investigation on the Electronic and Charge Transport Characteristics of Push-Pull Molecules for Organic Photovoltaic Cells. Synth. Met. 2014, 194, 118-125. (60) Murray, J. S.; Politzer, P. The Electrostatic Potential: An Overview. Wiley

Interdiscip. Rev.: Comput. Mol. Sci. 2011, 1, 153-163. (61) Duan, Y. A.; Li, H. B.; Geng, Y.; Wu, Y.; Wang, G. Y.; Su, Z. M. Theoretical Studies on the Hole Transport Property of Tetrathienoarene Derivatives: The Influence of the Position of Sulfur Atom, Substituent and π-Conjugated Core. Org. Electron.

2014, 15, 602-613. (62) Politzer, P.; Murray, J. S. The Fundamental Nature and Role of the Electrostatic Potential in Atoms and Molecules. Theor. Chem. Acc. 2002, 108, 134-142. (63) Laio, A.; VandeVondele, J.; Rothlisberger, U. D-RESP: Dynamically Generated Electrostatic Potential Derived Charges from Quantum Mechanics/molecular Mechanics Simulations. J. Phys. Chem. B 2002, 106, 7300-7307. (64) Laio, A.; Gervasio, F. L.; VandeVondele, J.; Sulpizi, M.; Rothlisberger. U. A Variational Definition of Electrostatic Potential Derived Charges. J. Phys. Chem. B

2004, 108, 7963-7968. (65) Zhu, W.; Perebeinos, V.; Freitag, M.; Avouris, P. Carrier Scattering, Mobilities, 31



and Electrostatic Potential in Monolayer, Bilayer, and Trilayer Graphene. Phys. Rev. B

2009, 80, 235402. (66) Mott, N. F.; Davis, E. A. Electronic Processes in Non-Gystalline Materials; Clarendon: London, 1979. (67) Singh, R.; Tandon, R. P.; Panwar, V. S.; Chandra, S. Low ‐ Frequency ac Conduction in Lightly Doped Polypyrrole Films. J. Appl. Phys. 1991, 69, 2504-2511. (68) Nair, K.; Mitra, S. S. Electrical Properties and Hopping Transport in Amorphous Silicon Carbide Films. J. Non-Cryst. Solids 1977, 24, 1-17. (69) Chen, X. P.; Jiang, J. K.; Liang, Q. H.; Yang, N.; Ye, H. Y.; Cai, M.; Shen, L.; Yang, D. G.; Ren, T. L. First-Principles Study of the Effect of Functional Groups on Polyaniline Backbone. Sci. Rep. 2015, 5. 16907. (70) Chen, X. P.; Liang, Q. H.; Jiang, J. K.; Wong, Cell K. Y.; Leung, Stanley Y. Y.; Ye, H. Y.; Yang, D. G.; Ren T. L. Functionalization-Induced Changes in the Structural and Physical Properties of Amorphous Polyaniline: A First-Principles and Molecular Dynamics Study. Sci. Rep. 2016, 6. 20621.

32


Page 32 of 34

Page 33 of 34 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


TOC Graphic

33



35x15mm (600 x 600 DPI)


Page 34 of 34

Wormlike Acid-Doped Polyaniline: Controllable Electrical Properties

Recommend Documents