STUDIES ON THE ELECTRICAL CONDUCTIVITY OF FREE-STANDING FILMS OF POLYANILINE

An insulate to metal transition was investigated based on the measurements of the dependence of the conductivity, activation energy on the protonation state of polyaniline (PANI). An isotropy in conductivity for stretched salt form of PANI was observed.For salt film of PANI, the Ⅰ-Ⅴ curve obeys Ohm's law, which shows a typical metal behavior, however, for base film or film with low protonation state, it can be explained by Space Charge Limited Current (SCLC). It is also found that the Ⅰ-Ⅴ curve of base film of PANI is independent of the work function of electrodes and the polymerization temperature.

Flexible free-standing graphene-like film electrode for supercapacitors by electrophoretic deposition and electrochemical reduction

Electrophoretic deposition in conjunction with electrochemical reduction was used to make flexible free-standing graphene-like films. Firstly, graphene oxide （GO） film was deposited on graphite substrate by electrophoretic deposition method, and then reduced by subsequent electrochemical reduction of GO to obtain reduced GO （ERGO） film with high electrochemical performance. The morphology, structure and electrochemical performance of the prepared graphene-like film were confirmed by SEM, XRD and FT-IR. These unique materials were found to provide high specific capacitance and good cycling stability. The high specific capacitance of 254 F/g was obtained from cyclic voltammetry measurement at a scan rate of 10 mV/s. When the current density increased to 83.3 A/g, the specific capacitance values still remained 132 F/g. Meanwhile, the high powder density of 39.1 kW/kg was measured at energy density of 11.8 W-h/kg in 1 mol/L H2SO4 solution. Furthermore, at a constant scan rate of 50 mV/s, 97.02% of its capacitance was retained for 1000 cycles. These promising results were attributed to the unique assembly structure of graphene film and low contact resistance, which indicated their potential application to electrochemical capacitors.

Conductive Polyaniline/Cellulose/Graphite Composite Films with High Thermal Stability and Antibacterial Activity

Functional composite films were successfully prepared from cellulose, graphite(GP), and polyaniline(PANI) using a combination of physical and chemical processes. Cellulosewasdissolved in N-methylmorpholine-N-oxide monohydrate(NMMO) and regenerated in water to form the matrix. GP was dispersed in the NMMO solvent prior to the dissolution of the cellulose, and PANI was deposited on the surfaces of the cellulose/GP films by in situ chemical polymerization. The structures of the PANI/cellusose/GP composite films were investigated using X-ray diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscopy(SEM), and SEM/energy-dispersive X-ray spectroscopy. The mechanical strengths, thermal stabilities, conductivities, and antibacterial activities of the films were studied in detail. The results showed that GP formed a multilayered structure in the cellulose matrix and that the PANI nanoparticles were tightly wrapped on the film surface. The film thickness increased from 40 mm to 100 mm after the addition of GP and PANI. The tensile strength of the composite films was 80~107 MPa, with the elongation at break being 3%~10%. The final residual weight of the composite films was as high as 65%, and the conductivity of the composite films reached 14.36 S/m. The cellulose matrix ensured that the films were flexible and exhibited desirable mechanical properties, while the GP filler significantly improved the thermal stability of the films. The PANI coating acted as a protective layer during burning and provided good electrical conductivity and antibacterial activity against Escherichia coli; both of these characteristics were slightly enhanced by the incorporation of GP. These PANI/cellulose/GP composite films should be suitable for use in electronics, antistatic packing, and numerous other applications.

Polyaniline-graphite composite film glucose oxidase electrode

A novel polyaniline-graphite composite film glucose oxidase （PGCF GOD） electrode was developed. The PGCF was synthesized by cyclic voitammetry method in 0.5 mol/L H2SO4 solution containing 1 g/L graphite powder and 0.2 mol/L aniline. The PGCF GOD electrode was prepared by doping GOD into the composite film. The morphology of the PGCF and the response property of the PGCF GOD electrode were investigated by scanning electron microscopy and electrochemical measurement, respectively. The results show that the PGCF has a porous and netty structure and the PGCF GOD electrode has excellent response property such as high sensitivity and short response time. Influences of pH value, temperature, glucose concentration and potential on the response current of the electrode were also discussed. The sensor has a maximum steady-state current density of 357.17μA/cm2 and an apparent Michaelis-Menten constant of 16.57 mmol/L. The maximum current response of the enzyme electrode occurs under the condition ofpH 5.5, 0.8 V and 65℃.

A review on polishing technology of large area free-standing CVD diamond films

Recently,with the rapid development of chemical vapor deposition(CVD)technology,large area free-standing CVD diamond films have been produced successfully.However,the coarse grain size on the surface and the non-uniform thickness of unprocessed CVD diamond films make it difficult to meet the application requirement.The current study evaluates several existing polishing methods for CVD diamond films,including mechanical polishing,chemical mechanical polishing and tribochemical polishing technology.

Synthesis of free-standing Ga_2O_3 films for flexible devices by water etching of Sr_3Al_2O_6 sacrificial layers

Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga_2O_3 thin films using the water-soluble perovskite Sr_3Al_2O_6 as a sacrificial buffer layer. The obtained Ga_2O_3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga_2O_3solar-blind UV photodetector was fabricated by transferring the free-standing Ga_2O_3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga_2O_3 photodetector were not sensitive to bending of the device. The free-standing Ga_2O_3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.

Characterization of Electrochromic Properties of Polyaniline Thin Films Electropolymerized in H2SO4 Solution

Polyaniline (PANI) onto indium-doped tin-oxide (ITO)-coated glass samples were prepared by electroopolymerization in 0.5 M H2SO4 solution. Structure and morphology characterization of the PANI films demonstrated that the films were grown onto ITO substrates in the form of polycrystalline microbelts separated by micropores. By analysing the UV-Vis absorption spectra of the PANI films, the energy bandgap was found to be approximately 2.75 eV. The PANI/ITO films exhibited a good reversible electrochromic display (ECD) performance when cycled in 0.1 M LiClO4 + pro-pylene carbonate. The response time of the ECD coloration was found to be as small as 15 s and the coloration efficiency was found to be 8.85 cm2 C-1. After 100 cycles of the ECD performance, the cyclic voltammetry curve of the working electrode maintained unchanged. This demonstrates that the electropolymerized PANI films can be served as a good candidate for ECD applications, taking advantage of their excellent properties in terms of chemical stability.

FREE STANDING FILM OF POLYANILINE

A free standing film of polyaniline as large as 18 cm×18cm×0.002 cm can be obtained by evaporation of a solution of the chemically synthesized base in NMP. Its structure was examined by the elemental analysis, IR, U.V.-visible spectra, XPS, DSC, SEM and X-ray scattering and its conducting behavior as well as electrochemical properties were studied. Results show that the composition, structure of main chain, physical properties of the free standing film of polyanilme is similar to that of the powder. However, some differences in its electronic structure, conductivity at room temperature and potential of redox couple between the flee standing film and powder are observed, which may be due to cross-linking of the film of polyaniline.

An Electrochemical Study on the Corrosion Inhibition of Stainless Steel by Polyaniline Film

Polyaniline (PANI) film was electrosynthesized on 304 stainless steel by cyclic voltammetry using aqueous oxalic acid as supporting electrolyte. The potential sweep rates were changed to achieve the PANI film with different thickness and structures. Protective properties of the PANI film for corrosion of stainless steel in 3% NaCl aqueous solution were investigated by monitoring potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The results showed that the PANI film which was formed with lower sweep rate led to more positive shift of corrosion potential and greater charge transfer resistance, reflecting higher inhibition for corrosion of the stainless steel.

Electrical resistance response of polyaniline films to water,ethanol,and nitric acid solution

This paper reports on electrical resistance vs. aging time for the response of polyaniline films under exposure to water, ethanol and nitric acid （HNO3） solution. Camphor sulfonic acid-doped polyaniline films were prepared by a ＂doping-dedoping-redoping＂ method, the morphology and microstructures of the films were characterized by a scanning electron microscope and an x-ray diffractometer, the electrical resistance was measured by a four-probe method. It was found that a lower amount of water molecules infiltrating the film can decrease the film＇s resistance possibly due to an enhancement of charge carrier transfer between polyaniline chains, whereas excessive water molecules can swell inter-chain distances and result in a quick increase of resistance. The resistance of the film under exposure to ethanol increases and becomes much larger than the original value. However, HNO3 solution can decrease the film＇s resistance sharply possibly owing to doping effect of protonic acid. These results can help to understand the conduction mechanism in polyaniline films, and also indicate that the films have potential application in chemical sensors.

STABILITY AND ELECTROCHEMICAL PROPERTIES OF FULL-CONJUGATED SELF-ASSEMBLED FILMS BASED ON POLYANILINE AND ITS ACID-SUBSTITUTED DERIVATES

The stability of full-conjugated self-assembled （SA） multilayer films based on partially doped polyaniline （PANI） as a polycation and poly（o-aminobenzoic acid） （PCAN）, poly（aniline-2-sulfonic acid） （PSAN） as polyanions is investigated in alkali aqueous solutions. The self-assembled PANI-PCAN films keep their stability within 24 h in 1 mol/L NaOH solution,-the PANI-PSAN films, however, maintain the stability for 20 min in the same condition because the solubility of PSAN in alkali solutions is much higher than that of PCAN. The electrochemical properties of the SA films are determined, and the film-CdS composites formed in situ are also reported.

Preparation and Properties of Polyaniline Composite Films

Polyaniline (PAn) was synthesized by chemical oxidation polymerization. The conductive polymer doped by camphor sulfonic acid (CSA) and a matrix polymer, polyamide66, polyamide1010 or polyamide11, were dissolved in m-cresol and the blend solution was cast in a glass and dried for preparing polyaniline composite films. Conductivity was from 10 -6 to 10 0 Ω -1 ·cm -1 with different weight fraction of PAn-CSA. The crystallization of the films was studied by means of differential scanning calorimeter (DSC). The treatment of the composite films in different pH value solution would result in decrease of conductivity, especially in an alkaline solution.

PHOTOELECTROCHEMICAL BEHAVIOR OF POLYANILINE FILM

The photoelectrochemical behavior of polyaniline(PAn)film was studied in aqueous electrolyte solution containing Fe(CN)_6^(3-)/Fe(CN)_+^(4-) redox couple.It was found that PAn films possess the properties of p-type semiconducter and a cathodic photocurrent as high as 700μA/cm^2 was observed when irradiated under polychromatic light of 100mW/cm^2.

Preparation of ZnO Thin Films on Free-Standing Diamond Substrates

Highly c-axis-oriented ZnO films were deposited successfully on the nucleation sides of free-standing diamond （FD） films by the direct current （DC） magnetron sputtering method. The effect of the sputtering parameters, such as power, gas pressure and sputtering plasma composition of Ar-to-O2, on the properties of ZnO thin films was investigated in detail. X-ray diffraction （XRD） measurements showed that, at a sputtering power of 200 W, gas pressure of 0.5 Pa and an Ar-to- O2 composition of 1：1, a higher intensity of the （002） diffraction peak and a narrower full width at half maximum （FWHM） were detected which meant high c-axis orientation and high quality of the ZnO films. To improve the quality of the ZnO film, a thin ZnO layer was pre-grown as a homo-buffer layer. XRD measurements showed that this buffer layer had a beneficial effect on the structural and morphological properties of the post-grown ZnO film.

Growth of Free-Standing Diamond Films on Stainless Steel

Free-standing diamond films have been successfully deposited on stainless steel substrates using microwave plasma-assisted chemical vapor deposition. Although iron, which is the main element of stainless steel, is known to inhibit the nucleation of diamond and enhance the formation of graphite, we were able to grow relatively thick films （-1.2 mm）. The films were easily detachable from the substrates. The poor adhesion made it possible to obtain free-standing diamond films without chemical etching. Raman spectroscopy showed the 1332 cm^-1 characteristic Raman peak of diamond and the 1580 cm^-1, 1350 cm^-1 bands of graphite on the growth surface and backside of the films, respectively. By energy dispersive X-ray spectroscopy it was only possible to detect iron on the back of the films, but not on the surface. The role of iron in the film growth is discussed.

Study on Electrical Property of Polyaniline Composite Film

Polyaniline was synthesized by chemically oxidative poly-merization.By means of infrared spectroscopy,the dif-ference between its intrinsic state structure and its dopedstate structure was determined for researching the rela-tionship between macromolecular structure and conduc-tive property before and after doping.The morphologyof solution-processed polyblends with the electricallyconductive polyaniline-camphor sulfonic acid complex(PAn-CSA)was investigated by using scanning electronmicroscopy.The conductive percolation threshold of thecomposite films is about 2.8%.

Highly efficient and wearable thermoelectric composites based on carbon nanotube film/polyaniline

Polyaniline(PANI)was prepared by in-situ polymerization and compounded on the two-dimensional network structural multi-walled carbon nanotube film(CNTF).Compared with the CNT/PANI composites fabricated by using CNT powders or dispersions,the compact and continuous network structure of CNTF/PANI is beneficial to both the thermoelectric and mechanical properties of the composites.The resultant CNTF/PANI composites with PANI polymerization time of 5 h obtain an electrical conductivity of 1338.4 S/cm and Seebeck coefficient of 63.3μV/K at 360 K,which are 168.7%and 5.7%higher than those of the CNTF(498.1 S/cm and 59.9μV/K at 360 K).Consequently,a maximum power factor of 536.8μW·m^(−1)·K^(−2) at 360 K is acquired,which is about 2 times higher than that of CNTF(181.7μW·m^(−1)·K^(−2) at 360 K).The electrical conductivity of the composites could maintain 93.3%after being bent for 500 times,indicating the excellent flexibility.The tensile strength,Young's Modulus and toughness of CNTF/PANI composites(232.3 MPa,3.6 GPa and 20.1 MJ/m^(3),respectively)are 3.5,2.6 and 2.1 times of those of the CNTF.The flexible,free-standing,lightweight and high-strength CNTF/PANI composites reveal the excellent thermoelectric performance,which are promising in the applications in wearable thermoelectric devices.

Mechanically flexible reduced graphene oxide/carbon composite films for high-performance quasi-solid-state lithium-ion capacitors

Practical applications of diverse flexible wearable electronics require electrochemical energy storage(EES)devices with multiple configurations.Moreover,to fabricate flexible EES devices with high energy density and stability,organic integration from electrode design to device assembly is required.To address these challenges,a free-standing reduced graphene oxide(rGO)/carbon film with a unique sandwich structure has been designed via the assistance of vacuum-assistant filtration for lithium-ion capacitors(LICs).The graphene acts as not only a binder to construct a three-dimensional conductive network but also an active material to provide additional capacitive lithium storage sites,thus enabling fast ion/electron transport and improving the capacity.The designed rGO/hard carbon(rGO/HC)and rGO/activated carbon(rGO/AC)free-standing films exhibit enhanced specific capacities(513.7 mA h g^(-1)for rGO/HC and 102.8 mA h g^(-1)for rGO/AC)and excellent stability.Moreover,the integrated flexible quasi-solid-state rGO/AC//rGO/HC LIC devices possess a maximum energy density of 138.3 Wh kg^(-1),a high power density of 11 kW kg^(-1),and improved cycling performance(84.4%capacitance maintained after 10,000 cycles),superior to the AC//HC LIC(43.5%retention).Such a strategy enlightens the development of portable flexible LICs.

蚕丝基柔性压力传感器的制备及其性能研究

蚕丝具有优异的生物相容性、可降解性和易加工性等,是应用于柔性电子领域的理想柔性基底材料。本文通过气液界面聚合法,在蚕丝织物、平板丝和静电纺丝素膜三种蚕丝材料表面实现聚苯胺的原位生长,成功制备出以聚苯胺为活性导电介质的柔性基材,并将其组装成柔性压阻式压力传感器,这为开发高性能、安全可靠和轻质便携的可穿戴电子产品提供新的方法和途径。结果表明:三种蚕丝基柔性压力传感器中,蚕丝织物聚苯胺传感器具有最大的压力检测范围(16.27~504.79 kPa),拉伸变形可达20%,灵敏度仅为0.00129 kPa^(-1);静电纺丝素膜聚苯胺传感器灵敏度最高(0.01376 kPa^(-1)),但拉伸变形能力差,仅可拉伸2.3%;平板丝聚苯胺传感器压力检测灵敏度略高于蚕丝织物聚苯胺传感器,达到0.00134 kPa^(-1),线性检测范围为9.8~87.6 kPa。本文研究开发的蚕丝基柔性压力传感器在运动检测领域具有较好的应用前景。

Graphene film for thermal management:A review

Thermal conductivity and thermal dissipation are of great importance for modern electronics due to the increased transistor density and operation frequency of contemporary integrated circuits.Due to its exceptionally high thermal conductivity,graphene has drawn considerable interests worldwide for heat spreading and dissipation.However,maintaining high thermal conductivity in graphene laminates(the basic technological unit)is a significant technological challenge.Aiming at highly thermal conductive graphene films(GFs),this prospective review outlines the most recent progress in the production of GFs originated from graphene oxide due to its great convenience in film processing.Additionally,we also consider such issues as film assembly,defect repair and mechanical compression during the post-treatment.We also discuss the thermal conductivity in in-plane and through-plane direction and mechanical properties of GFs.Further,the current typical applications of GFs are presented in thermal management.Finally,perspectives are given for future work on GFs for thermal management.