Synthesis,characterization, and morphology of p‐toluene sulfonic acid‐doped polyaniline: A material for humidity sensing application

Polyaniline (PANI) doped with p‐toluene sulfonic acid was synthesized by chemical polymerization method using (NH₄)₂S₂O₈ as an oxidizing agent. This is a single step polymerization process for the direct synthesis of the conducting emeraldine salt (ES) phase, without the need of doping, dedoping, and redoping of the polymer. Presence of a free carrier tail at higher wavelength, characteristic of extended coil conformation along with a sharp polaronic peak is observed in the UV–vis spectrum of doped PANI in m‐cresol solvent. FT‐IR studies show the characteristic peaks of ES phase along with a sharp peak at 1120 cm^?1 representing vibration band of the dopant ion. Clumps of small fibers resulting in a sponge‐like structure was observed under scanning electron microscope. Thermal studies revealed a three‐step decomposition pattern. Conductivity is found to increase with an increase in the temperature showing “thermal activation behavior.” Decrease in resistance with increasing humidity is observed in a broad range of humidity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2161–2169, 2005     

Electrical transport properties of an organic semiconductor on polyaniline doped by boric acid

The electrical conductivity, thermoelectric power, and dielectric properties of polyaniline doped by boric acid (PANI‐B) have been investigated. The room temperature electrical conductivity of PANI‐B was found to be 1.02 × 10^?4 S cm^?1. The thermoelectric power factor for the polymer was found to be 0.64 µW m^?1 K^?2. The optical band gap of the PANI‐B was determined by optical absorption method, and the PANI‐B has a direct optical band gap of 3.71 eV. The alternating charge transport mechanism of the polymer is based on the correlated barrier hopping (CBH) model. The imaginary part of the dielectric modulus for the PANI‐B suggests a temperature dependent dielectric relaxation mechanism. Electrical conductivity and thermoelectric power results indicate that the PANI‐B is an organic semiconductor with thermally activated conduction mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of polyaniline doped with organic acids

Spectroscopic [UV–visible and Fourier transform IR (FTIR)] and thermal properties of chemically synthesized polyanilines are found to be affected by varying the protonation media (acetic, citric, oxalic, and tartaric acid). The optical spectra show the presence of a greater fraction of fully oxidized insulating pernigraniline phase in polyaniline doped with acetic acid. In contrast, the selectivity in the formation of the conducting phase is higher in oxalic acid as a protonic acid media. The FTIR spectra of these polymers reveal a higher ratio of the relative intensities of the quinoid to benzenoid ring modes in acetic acid doped polyaniline. Scanning electron micrographs revealed a sponge‐like structure derived from the aggregation of the small granules in acetic acid and oxalic acid doped polyaniline. A three‐step decomposition pattern is observed in all the polymers, regardless of the protonic acid used for the doping. The second step loss related to the loss of dopant is found to be higher in the oxalic acid doped polymer. In accordance with these results the conductivity is also found to be higher in oxalic acid doped material. The temperature dependent conductivity measurements show the thermal activated behavior in all the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2043–2049, 2004     

The role of molecular recognition in charge transport properties of doped polyaniline

Molecular recognition plays a significant role in the counterion-induced processibility, morphological features, and physical properties of doped polyaniline (PANI). The interaction of the counterion and solvent controls the chain conformation and, as a result, the formation of extended and localized electronic states; hence, it holds the key for tuning a wide range of electrical and optical properties of doped PANI. The combined effects of counterion, solvent, and processing conditions tune the metal-insulator transition, temperature dependence of conductivity, magnetoresistance, and so forth in doped PANI. The typical examples are shown in the case of PANI doped by camphor sulfonic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, and dodecylbenzoyl sulfonic acid.     

导电聚苯胺/钙基膨润土复合材料的制备

采用插层聚合法制备了导电聚苯胺/钙基膨润土、聚苯胺/有机化膨润土复合材料.以电导率为考核指标,通过正交设计优化了苯胺的加入量、反应温度和反应时间等参数.结果表明,苯胺的加入量影响较显著,反应温度对聚苯胺/有机化膨润土复合材料影响较聚苯胺/钙基膨润土体系明显,反应时间的延长,有利于聚苯胺/有机化膨润土复合材料电导率的提高.聚苯胺/钙基膨润土复合材料制备的最佳工艺条件为:苯胺加入量为70%,反应温度为0℃,反应时间为6 h;聚苯胺/有机化膨润土复合材料制备的最佳工艺条件为:苯胺加入量为70%,反应温度为室温,反应时间为8 h.利用红外光谱(FT-IR)、X射线衍射(XRD)和四探针技术表征了材料的组成、结构和性能.结果表明:膨润土经有机化后,晶面间距增大较多;苯胺单体与钙基膨润土插层聚合后,膨润土晶面间距增大不多;苯胺单体与有机化膨润土复合后,破坏了膨润土的晶格结构,形成了混杂复合体系,电导率达10-3S.cm-1.     

Structural effect of polymeric acid dopants on the characteristics of doped polyaniline composites: Effect of hydrogen bonding

The conductivities of polyaniline (PANi) composites doped with the copolymeric acids such as poly(methyl methacrylate-co-p-styrenesulfonic acid) (PMMA-co-SSA), poly(styrene-co-p-styrenesulfonic acid) (PS-co-SSA), and poly(methyl methacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (PMMA-co-AMPS) were investigated as a function of the acid content in the copolymeric acid dopants. With the fixed ratio of acid to aniline (1/1) in the PANi composites, the conductivities of the copolymeric acid-doped PANis decreased as the acid content in the copolymeric acids decreased. This could be attributed to the nonacidic units in the copolymeric acids which seemed to prevent adjacent acid groups from doping the PANi. Among the three kinds of copolymeric acid dopants, the PMMA-co-SSA series doped the PANi most effectively, and consequently, the PMMA-co-SSA-doped PANi composites showed the highest conductivities. The lack of conductivities of the PMMA-co-AMPS-doped PANi composites seems to be due to the doping ability of the AMPS groups. The higher conductivities of the PMMA-co-SSA-doped PANi composites rather than the PS-co-SSA-doped ones were attributed to the hydrogen bonding formed between the carbonyl groups in MMA and the amine groups in aniline which may hinder the phase separation and induce more homogeneous mixing and efficient doping. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1431–1439, 1998     

Conduction behavior of doped polyaniline films at high current density regime

The conduction behavior at high current density at room temperature and above of polyaniline (PANI) films doped with HCl and camphor sulfonic acid (HCSA), respectively, is reported. It is found that the current density deviates strongly from the linear relation with the electric field in high current density region, and a saturation of the current density is observed. The maximum current density J_m seems to be proportional to the conductivity of the sample and hence, for PANI doped with HCl, J_m is about 200 A/cm^2, whereas for HCSA doped samples, J_m can reach more than 1,200 A/cm². The saturation of current density is interpreted as being caused by space charge accumulation at the insulating barrier regions and a dedoping effect in the conduction domains due to the detraping of the ions under high fields. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2845–2850, 1999     

Electrical conductivity enhancement of polyaniline by refluxing

The room temperature electrical conductivity of polyaniline (PANI) was found to increase remarkably after it was heated in tetrahydrofuran (THF) with refluxing for a certain period and then doped with methanesulfonic acid (MSA). The enhanced electrical conductivity of PANI was attributed to a partially cross‐linked network generated via the formation of new chemical bonds between adjacent PANI chain segments during thermal treating, which may shorten the inter‐chain distance and facilitate inter‐chain transition of charge carriers in doped PANI. During the refluxing, the moderate dissolving power for PANI as well as a much lower boiling point of THF were considered to have a unique effect on the formation of such partially cross‐linked network in PANI. As a comparison, PANI treated in poor solvents like methanol (or ethanol) and PANI treated in dimethyl formamide (DMF), which is a better solvent than THF but has higher boiling point, did not show an obviously increased electrical conductivity. Study on X‐ray diffraction (XRD) analysis of PANI after refluxing showed that crystallinity decreased gradually with the increase of cross‐linking degree, but the inter‐chain cross‐linking probably occurred first in crystalline region and then in the amorphous region. Electrical conductivity of PANI decreased after it was refluxed with THF for an extended period due to the decreased crystallinity and doping in PANI. Copyright © 2010 John Wiley & Sons, Ltd.     

Reduction of silver nitrate by polyaniline nanotubes to produce silver-polyaniline composites

Polyaniline (PANI) nanotubes were prepared by oxidation of aniline in 0.4 M acetic acid. They were subsequently used as a reductant of silver nitrate in 1 M nitric acid, water or 1 M ammonium hydroxide at various molar ratios of silver nitrate to PANI. The resulting PANI-silver composites contained silver nanoparticles of 40–60 nm size along with macroscopic silver flakes. Under these experimental conditions, silver was always produced outside the PANI nanotubes. Changes in the molecular structure of PANI were analyzed by FTIR spectroscopy. Silver content in the composites was determined as a residue by thermogravimetric analysis, and confirmed by density measurements. The highest conductivity of a composite, 68.5 S cm⁻¹, was obtained at the nitrate to PANI molar ratio of 0.67 in water. Also, the best reaction yield was obtained in water. Reductions performed in an acidic medium gave products with conductivity of 10⁻⁴–10⁻² S cm⁻¹, whereas the reaction in alkaline solution yielded non-conducting products.     

Electronic transport properties of polyaniline/PVC blends

The electrical conductivity and thermoelectric power of polyaniline/PVC blends was measured. Surprisingly, the conductivity of the blends is greater at low temperatures than that of the pure polyaniline sample. The conductivity follows approximately an exp (?T^?1/2) law over a considerable range of temperature, with deviations from this law observed at high temperature increases (with positive sign) except at very low temperatures, where negative peaks are observed. Possible models to interpret these observations are mentioned. © 1993 John Wiley & Sons, Inc.     

Synthesis and Characterization of Conducting Polyaniline Doped with Polymeric Acids

Conducting polyaniline doped with polymeric acids was synthesized by a in situ chemical polymerization method. The synthesized polymers were characterized by using UV‐Visible, FT‐IR spectroscopy and SEM analysis. Thermal stability of these polymers was evaluated by using TGA/DSC analysis. Among the three polymeric acids used for doping purpose, poly(vinyl sulphonic acid) doped polyaniline is found to be more conducting than those doped with other acids. From the temperature dependent conductivity measurements, an increase in conductivity with increase in temperature was observed.     

Structure and properties of plasma-polymerized thin films of polyaniline

Plasma polymerization of aniline and in-situ doping of polvaniline with iodine was carried out using radio frequency glow discharge. Thin films of polyaniline were deposited on platinum and glass. The infrared spectrum shows that the aromatic ring is retained under the plasma conditions. The electrical conductivity measurements indicate that the conductivity increases by more than seven orders of magnitude when the polyaniline is doped by iodine. The scanning electron microscopic studies reveal the formation of irregular pentagons on glass substrate while on platinum, polvaniline forms a fibrillar network. In both the cases a continuous film is obtained.     

Temperature- and humidity-related degradation of conducting polyaniline films

The time dependence of dc conductivity of conducting polyaniline films was measured in relation to temperature and relative humidity of the environment. Optical and structural properties of the samples were checked using Fourier transform infrared (FTIR) spectroscopy.     

Electrical properties and EMI shielding behavior of highly thermally stable polyaniline/colloidal graphite composites

A hybrid approach has been adopted by using a combination of colloidal graphite (CG) as a conducting filler, 5‐lithium sulfoisophthalic (LiSIPA) acid as a dopant, and polyaniline (PANI) as a matrix to prepare LiSIPA doped PANI–CG composites. The thermal stability (～300°C) and electrical conductivity (67.4 S/cm at 17.4% CG content) have been improved significantly as compared to PANI doped with conventional inorganic dopants like HCl or H₂SO₄ (130–150°C). The maximum shielding effectiveness value was found to be ?39.7 dB. X‐ray diffraction and infrared spectroscopy showed a systematic shifting of the characteristic peaks and bands with increase in the amount of CG, which indicates significant interaction exists between CG and PANI. The UV–Vis spectra showed the characteristic bands of PANI, with a shift to shorter wavelength with increase in the CG content. The interaction mechanism between doped PANI and CG in the resultant composites has been proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of supporting electrolyte on the electrochemical synthesis,morphology, and conductivity of polyaniline

Electrochemical synthesis of polyaniline (PANI) was carried out under cyclovoltammetric conditions using H₂SO₄, HCl, HNO₃, and HClO₄ as supporting electrolytes. The observed different rate of PANI deposit growth depending on the acid in the solution has been explained on the grounds of a different degree of specific adsorption for particular anion. It has been found that morphology of the deposit depends greatly upon the anion present in the solution. Thus, PANI synthesized from the solution of oxyacids results in a dense sponge-like structure while PANI from the hydrochloric acid solution results in a spaghetti-like structure. The structure of the deposit influences the conductivity, being higher for a dense deposit from oxyacid solutions and three orders of magnitude lower in case of a deposit from hydrochloric acid solution. © 1994 John Wiley & Sons, Inc.     

盐酸掺杂聚苯胺的制备及性能研究

本文用溶液聚合法制备盐酸掺杂聚苯胺,测定了体系酸度对聚苯胺电导率的影响,及盐酸掺杂聚苯胺在不同条件下经过热处理后的电导率,采用TGA、XRD等方法,研究了热处理过程对聚苯胺结构的影响。结果表明,当热处理温度为90℃时,电导率高于初始值,当热处理温度高于100℃时,电导率开始下降,到达220℃时,电导率下降了约4个数量级。在氮气中聚苯胺电导率的衰减比空气中小,聚苯胺经热处理后在浓硫酸中的溶解性会明显降低。本文还探讨了去掺杂、氧化和化学交联等盐酸掺杂聚苯胺的热降解机理。     

Ternary composites of multi-wall carbon nanotubes,polyaniline, and noble-metal nanoparticles for potential applications in electrocatalysis

Multi-wall carbon nanotubes were coated with a conducting polymer, polyaniline phosphotungstate. Such composite structures have mixed electronic and proton conductivity, high surface area and porosity. These materials were decorated with catalytically-active noble metals — Pt, Pd, and Rh. Metal nanoparticles were uniformly distributed in the polymer matrix. Such ternary composites can be considered as electrode materials in sensors, electrolysers, supercapacitors, and especially in low-temperature fuel cells with a proton-conducting polymer membrane.     

Facile preparation of highly conductive,flexible, and strong carbon nanotube/polyaniline composite films

In general, the high electrical conductivity (EC) comes into conflict with the good flexibility and high strength of carbon nanotube (CNT)/polyaniline (PANI) composites. In other words, a high CNT content will bring about a high EC but lead to a low flexibility and strength due to the CNT‐constrained matrix deformation and CNT aggregation. In this work, a highly conductive, flexible and strong CNT/PANI composite film prepared via a facile solvent‐evaporation method is readily obtained by a cold stretching. The cold stretching is conducted at room temperature for the CNT/PANI film. It is observed that the cold stretching process leads to an unexpectedly enhanced EC. The as‐obtained EC of 231 S/cm is much higher than that (2 – 50 S/cm) of the previously reported CNT/PANI composite films. Meanwhile, the strength is obviously improved over that of the pure PANI film and the good flexibility is maintained to a high degree by the introduction of a proper CNT content. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1575–1585     

Synthesis and characterization of methanesulfonic acid doped poly(2-chloroaniline), study of its physical properties and ammonia gas sensing application

The poly(2-chloroaniline) was prepared by in situ chemical oxidative polymerization method using ammonium thiosulphate as an oxidant and methanesulfonic acid as a dopant. The optical absorption spectra showed bands for π-π* transition of the benzenoid ring at 265 nm and at 350 nm for n-π* transition of the quinonoid ring. The broad band appeared around 550 nm was due to transition of electrons from the valance band to the conduction band, this also confirmed the good electrical conductivity of the polymer. The X-ray diffraction pattern showed characteristic diffraction peak at 2θ = 26° confirming a emeraldine salt form of the poly(2-chloroaniline). The electrical conductivity of the polymer measured by the two probe method at room temperature was 2.21×10^?3 S/cm, which was found to be thermally activated. The linear increase in conductivity with increase in the temperature suggested the electron hopping mechanism. The methanesulfonic acid doped poly(2-chloroaniline) presents a linear dependency of its electrical resistance with an increase in ammonia gas concentration (1 ppm to 300 ppm) and creates a promising sensing material for ammonia gas sensing applications.