Electrochromic properties of a novel low band gap conductive copolymer

A copolymer of 2,5-di(thiophen-2-yl)-1-p-tolyl-1H-pyrrole (DTTP) with 3,4-ethylene dioxythiophene (EDOT) was electrochemically synthesized. The resultant copolymer P(DTTP-co-EDOT) was characterized via cyclic voltammetry, FTIR, SEM, conductivity measurements and spectroelectrochemistry. Copolymer film has distinct electrochromic properties. It has four different colors (chestnut, khaki, camouflage green, and blue). At the neutral state λ_max due to the π-π^* transition was found to be 487 nm and E_g was calculated as 1.65 eV. Double potential step chronoamperometry experiment shows that copolymer film has good stability, fast switching time (less than 1 s) and good optical contrast (20%).An electrochromic device based on P(DTTP-co-EDOT) and poly(3,4-ethylenedioxythiophene) (PEDOT) was constructed and characterized. The device showed reddish brown color at −0.6 V when the P(DTTP-co-EDOT) layer was in its reduced state; whereas blue color at 2.0 V when PEDOT was in its reduced state and P(DTTP-co-EDOT) layer was in its oxidized state. At 0.2 V intermediate green state was observed. Maximum contrast (%ΔT) and switching time of the device were measured as 18% and 1 s at 615 nm. ECD has good environmental and redox stability.     

Formation of conductive polyaniline nanoarrays from block copolymer template via electroplating

Nanostructured thin films have drawn extensive attention because of their unique properties resulting from nanoscale features. One of the convenient ways to generate nanostructured thin films is to use pattern with nanoscale texture as a template for the reactions carrying out within the template. In this study, nanoporous thin film template was obtained from the self-assembly of degradable block copolymer, polystyrene-b-poly(l-lactide) (PS-PLLA) with PLLA cylinder nanostructure, at which the PLLA block can be hydrolyzed to form the nanopatterns with cylinder nanopores on conductive substrate (i.e., ITO substrate). The nanoporous PS thin film template was stabilized by modification of substrate using hydroxyl terminated PS so as to enhance the adhesion with substrate for following electroplating process. Combining a pulse electroplating method with the control of micro current, polyanilines can be successfully synthesized within the template to fabricate well-defined of conductive polymer nanoarrays.     

Chemical sensing materials. I. Electrically conductive SEBS copolymer systems

Chemical sensing materials based on conductive carbon black (CB) filled [styrene‐ethylene butylene‐styrene] triblock‐copolymers (SEBS) were investigated. Several types of SEBS copolymers were studied, differing in composition and melt viscosity. The sensing is based on electrical conductivity changes upon solvent sorption/desorption. Compression molding SEBS composites containing various amounts of CB were prepared. Their electrical conductivity was measured and samples containing CB, preferentially located in the continuous ethylene/butylene (EB) phase, at a level near the corresponding percolation threshold were used for the sensing experiments. The conductivity was measured during several exposure/drying cycles. Structure characterization included scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and calorimetry (DSC). The SEBS composites exhibit large reversible changes in conductivity upon exposure to a limited number of solvents, e.g., acetone, n‐heptane, and air drying cycles. This behavior was related to the sorption kinetics, affected by the solvent characteristics (solubility parameter, polarity, molecular volume and vapor pressure). The samples' resistance tended to return to their initial value upon short drying of acetone, and longer drying of other studied solvents. The nature of the SEBS, the CB content, and mixing temperature are all significant parameters, determining the sample's structure and the resultant sensing property. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermally conductive adhesives from covalent-bonding of reduced graphene oxide to acrylic copolymer

This work reports about the enhancement of the thermal conductivity of an acrylic pressure-sensitive adhesive (PSA) with the incorporation of functionalized and reduced graphene oxide (frGO) sheet in the composition. Bifunctional isocyanatoethylmetharcylate (IEMA) was intercalated (so-called ‘functionalization’) to the GO surface mainly at its –COOH sites. The remaining oxygenated groups on the GO surface were reduced by dimethyl hydrazine. The frGO was successfully incorporated into PSA matrix through in-situ polymerization of acrylic monomers and subsequently crosslinked under UV radiation. The conductivity and the peel strength of the PSA were studied as a function of filler content, filler modification (functionalization and/or reduction), UV-radiation dosage and mode of filler insertion (through in-situ polymerization or mechanical mixing). frGO/PSA showed much better properties than the PSA system with bare or IEMA-functionalized unreduced GO. In-situ polymerization was found to be more effective method for frGO insertion. Within the range of filler content (0.0–1.0) wt% and UV-radiation dosages of (400–3000) mJcm^?2, the thermal conductivity and peel strength of the acrylic PSA-system under investigation varied in the range of 0.17–1.03 Wm^?1K^?1 and 2831–299 g_f/25 mm. This is the first report on ‘reduced GO covalently bonded to polymer chain in an adhesive-composition’ providing novel idea to make PSA-system with balanced thermal conductivity and peel strength with perspective for application in miniature electronic industries.     

Dielectric relaxation of conductive carbon black reinforced ethylene‐octene copolymer vulcanizates

The dielectric relaxation behavior of different conducting carbon black‐filled ethylene‐octene copolymer (EOC) vulcanizates prepared by melt‐mixing method has been studied as a function of frequency (100 Hz–5 MHz) over a wide range of temperatures (25–100°C). The effect of filler loading and frequency on AC conductivity, dielectric permittivity, impedance, and dielectric loss tangent (tanδ) has been studied. The nature of variation of the dielectric permittivity with the filler loadings was explained on the basis of interfacial polarization of the filler in the polymer matrix. The effect of filler loading on the real and complex part of the impedance was explained by the relaxation dynamics of the polymer chains in the vicinity of the fillers. The effect of filler and temperature on dielectric loss tangent, dielectric permittivity, AC conductivity, and Nyquist plot was also reported. The bound rubber (BR) value increases with increase in filler loading suggesting the formation of strong interphase, which is correlated with dielectric loss. Thermal activation energy (E_a) was found to be decreasing with the temperature, which follows the Arrhenius relation: τ_b = τ₀ exp(−E_a/K_BT) where τ_b is the relaxation time for the bulk material. From the plot of lnτ_b versus inverse of absolute temperature (1/T), the activation energies (E_a) were found to be 0.37 and 0.44eV, respectively. The percolation threshold was observed with 40 phr carbon black loading. POLYM. COMPOS., 37:342–352, 2016. © 2014 Society of Plastics Engineers     

Reactive processing and evaluation of butadiene–styrene copolymer/polyaniline conductive blends

Blending is an important way to obtain materials based on intrinsically conductive polymers and conventional plastics and rubber materials. Much research has been carried out to determine the best performance of materials be used for electrostatic dissipation and electromagnetic interference shielding. Mechanical mixing, codissolution, and in situ polymerization have been used to prepare these materials. The method used depends on the host polymer and its thermal stability and acid attack resistance. Homogeneity and miscibility are properties that should be controlled during blend preparation. In this study, we prepared a conductive thermoplastic elastomer material based on butadiene–styrene copolymer (SBR) and polyaniline (PANI) doped with dodecylbenzene sulfonic acid (DBSA) and poly(styrene sulfonic acid) (PSS). PSS also acted as compatibilizer between PANI and SBR. PANI was doped by reactive processing with DBSA and PSS to produce the conductive complex PANI–DBSA–PSS. This complex was mixed with 90, 70, and 50% (w/w) SBR in a counterrotatory internal mixer. Conductivity tests, swelling studies, thermal analysis, and mechanical property and reflectivity testing were done, and the results show a strong dependence on PANI concentration and the ratio between PANI–DBSA and PSS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 681–685, 2006     

Bulk conductive polymers prepared from nylon‐6/6,9 copolymer/CuCl2 compounds

Semiconductive polymers were obtained by soaking nylon‐6/6,9 particles in concentrated CuCl₂·2H₂O aqueous solutions, followed by reduction of the treated particles with sodium borohydride aqueous solutions. The reduced nylon‐6/6,9/CuCl₂ particles were compression molded at a relatively low temperature (160°C). The bulk volume resistivity obtained is at an intermediate level, ～10⁵ ohm‐cm. The compounds generated by reduction of the nylon‐6/6,9/CuCl₂ particles were determined to consist of metallic copper by means of energy‐dispersive X‐ray microanalysis. The metallic copper is responsible for the electrical conductivity of the bulk samples. Samples stored at the ambient atmosphere gradually absorb oxygen and moisture, resulting in a decrease in the conductivity. The morphology of nylon‐6/6,9/CuCl₂ samples before and after reduction was studied by a scanning electron microscope and transmission electron microscope. A two‐level hierarchy structure, submicrometer and nano‐sized, of copper particles was observed, forming the conducting copper networks. Molded samples of reduced nylon‐6/CuCl₂ and nylon‐6,6/CuCl₂ particles, prepared by the same procedure as that of nylon‐6/6,9/CuCl₂ particles, were insulating, whereas a reduced nylon‐6/CuCl₂ film was moderately conductive. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1367–1373, 2004     

Design of sandwich structure conductive polypropylene/styrene-butadiene-styrene triblock copolymer/carbon black composites with inherent morphological tunability

The insulator-conductor transition of conductive polymer composites (CPCs) can be ascribed to the fabrication of conductive networks, and the morphology of conductive networks plays a significant role in the electrical conductivity. This study presents CPCs with inherent morphology tunability which can be controlled by kinetic methods (i.e., mixing procedures and sequences, and polymer melt viscosity). Polypropylene (PP)/styrene-butadiene-styrene block copolymer (SBS) (50/50, in volume)/10 phr (parts per hundred of the polymer matrix) conductive carbon black (CB) composites prepared by different compounding sequences (PP/CB composites mixed with SBS, SBS/CB composites mixed with PP, and PP/SBS blend mixed with CB) are named as PC₁₀S, SC₁₀P, and PSC₁₀. With the difference between the phase morphologies, distribution, and dispersion of CB, the PP/SBS/CB composites realize seven orders of magnitude difference in resistivity. The volume resistivity (ρ_v) of PC₁₀S SC₁₀P and PSC₁₀ are 1.57 × 10¹, 1.68 × 10², and 4.88 × 10⁸ Ω m, respectively.     

Relations between molecular mixing state and conductive property in blends composed of polyaniline and aliphatic copolymer having acid groups

Blend films composed of polyaniline and aliphatic copolymer having carboxylic acid groups were prepared by vaporizing a solvent from a solution of both polymers. Poly(methyl methacrylate‐co‐methacrylic acid) and poly(1‐vinylpyrrolidone‐co‐acrylic acid) were used as the copolymers in this work. Conductivity of the blend film increased with decreasing concentration of polyaniline and then decreased in the region of low concentration. The N_1s peak in the ESCA spectrum of the blend film was shifted to higher binding energy with decreasing concentration of polyaniline and then was done to lower the binding energy in the region of low concentration. Polyaniline chains in the blend films become conductive by being oxidized with the carboxylic acid groups, which are the constituents of the copolymers. Through strong intermolecular interactions such as ionic bonding and hydrogen bonding between polyaniline and the copolymer, densities of the blend films are always higher than those predicted on the basis of the additive law. Blend films with higher density and higher conductivity are able to be prepared with a higher vaporizing rate, given that phase separation occurring during vaporizing process can be depressed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1113–1117, 2002     

Electrically conductive polycarbonate/ethylene‐propylene copolymer/multi‐walled carbon nanotubes nanocomposites with improved mechanical properties

In this article, the effect of Multi‐walled carbon nanotubes (MWCNTs) on the electrical conductivity and mechanical properties of polycarbonate (PC) toughened with cross‐linked ethylene‐propylene copolymer (EPC) was investigated. The solubility parameters of the PC and EPC were calculated using Hoy methods to clarify the miscibility of the polymer blends. It could be concluded that in the cooled state, the blends form a heterogeneous structure with two separate phases. The tensile, flexural, impact toughness properties of the PC/EPC blend and PC/EPC/MWCNT nanocomposites were carried out to illuminate the optimum concentration of polymer blends and MWCNTs. The 335% increment for the impact strength results appeared with combination of 10% EPC in the PC matrix. The flexural modulus and strength of PC/EPC blend increased by 75.1% and 59.1%, respectively. The Nielsen model was performed to fit the best curve of theoretical simulation to experimental results for elastomeric dispersed in the plastic matrix. Halpin‐Tsai model was applied to estimate the stiffness of nanocomposites blends with different volume fraction and aspect ratio of MWCNTs in the PC/EPC blends. Finally, in the presence of MWCNTs, all nanocomposite samples were semi‐conducting and the percolation threshold of the PC/EPC (10%) blends was between 0.5% and 1.0% MWCNTs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44661.     

导电胶固化过程中导电网络形成的机理

研究了环氧树脂导电胶固化过程中电阻的变化与电极之间距离的关系，根据实验结果提出了如下观点：导电胶在固化过程中由不导电变为导电，是由于导电填料颗粒凝聚成为导电团簇并进一步形成导电网络。固化时体积收缩固然对电阻降低有一定贡献，但是和导电团簇形成相比它的重要性是第二位的。银粉颗粒凝聚形成导电网络与吸附在表面上的分散剂有密切的关系。     

铜粉添加型导电胶的研制

以环氧树脂E-51为导电胶基体树脂、二乙烯三胺为固化剂,采用硅烷偶联剂(KH-550)对铜粉进行改性处理,并以此作为导电填料,制备了热固化各向同性导电胶。通过正交实验探讨了固化剂、硅烷偶联剂、还原剂、稀释剂和导电填料等因素对导电胶固化性能、粘接性能和导电性能的影响,并对导电胶的制备参数进行优化,得到了制备导电胶的最佳方案。实验结果表明,所制备的热固化各向同性导电胶具有制备工艺简单、粘接强度高(剪切强度≥20 MPa)和导电性能好(体积电阻率为1.50×10-3Ω·cm)等特点;经室温1000h老化实验后,导电胶的体积电阻率和剪切强度变化率<20%。     

High thermal conductive epoxy molding compound with thermal conductive pathway

The epoxy molding compound (EMC) with thermal conductive pathways was developed by structure designing. Three kinds of EMCs with different thermal conductivities were used in this investigation, specifically epoxy filled with Si₃N₄, filled with hybrid Si₃N₄/SiO₂, and filled with SiO₂. Improved thermal conductivity was achieved by constructing thermal conductive pathways using high thermal conductivity EMC (Si₃N₄) in low thermal conductivity EMC (SiO₂). The morphology and microstructure of the top of EMC indicate that continuous network is formed by the filler which anticipates heat conductivity. The highest thermal conductivity of the EMC was 2.5 W/m K, reached when the volume fraction of EMC (Si₃N₄) is 80% (to compare with hybrid Si₃N₄/SiO₂ filled‐EMC, the content of total fillers in the EMC was kept at 60 vol %). For a given volume fraction of EMC (Si₃N₄) in the EMC system, thermal conductivity values increase according to the order EMC (Si₃N₄) particles filled‐EMC, hybrid Si₃N₄/SiO₂ filled‐EMC, and EMC(SiO₂) particles filled‐EMC. The coefficient of thermal expansion (CTE) decreases with increasing Si₃N₄ content in the whole filler. The values of CTE ranged between 23 × 10^?6 and 30 × 10^?6 K^?1. The investigated EMC samples have a flexural strength of about 36–39 MPa. The dielectric constant increases with Si₃N₄ content but generally remains at a low level (<6, at 1 MHz). The average electrical volume resistivity of the EMC samples are higher than 1.4 × 10¹⁰ Ω m, the average electrical surface resistivity of the EMC samples are higher than 6.7 × 10¹⁴ Ω. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ethylene–(vinyl acetate) copolymer/carbon fiber conductive composite: effect of polymer–filler interaction on its electrical properties

Ethylene–(vinyl acetate) (EVA)/carbon fibre (CF) composites were prepared by changing the content of CF in the composite. To investigate the effect of the interaction between EVA and CF on the electrical properties of the composite, the CF was treated in nitric acid. The interaction between EVA and CF was examined by a solvent-extraction method. It was found that the interaction of EVA with CF was enhanced due to the chemical absorption of EVA on CF. The correlation of CF content, electrical properties and the formation of polymer–filler gel for the composite with oxidized CF was studied. Although the composites filled with treated CF exhibit a slightly higher resistivity than those filled with untreated CF at room temperature, they show the improved electrical properties, including elimination of the negative-temperature-coefficient (NTC) effect, high electrical reproducibility after thermal cycles, and independence of the conductivity on time, which improves the practical applications of positive-temperature-coefficient (PTC) materials. Copyright © 2004 Society of Chemical Industry     

导热型热塑性塑料

本文阐述了通过填充改性 ,可使热塑性塑料具有导热性 ,从而更适合用于代替金属材料作结构部件的场合     

石墨烯改性导电胶的制备及导电机理研究

以环氧树脂(EP)为基体、聚苯胺为助剂、铜粉为导电填料和石墨烯为改性剂,采用共混法制备了高导电性、高粘接强度、低成本和固化后不易开裂的导电胶,并对其导电机理进行了分析。研究结果表明:铜粉作为导电填料,可使导电胶的成本大幅降低,当w(铜粉)=60%(相对于EP质量而言)时,导电胶的导电性能相对最佳(体积电阻率为4.14×10~(-3)Ω·cm)。石墨烯可进一步改善导电胶的导电性能,当w(石墨烯)=0.05%(相对于EP质量而言)时,导电胶的体积电阻率(2.78×10~(-3)Ω·cm)相对最低。石墨烯在胶体内形成类似钢筋骨架作用的网络结构,使填料之间连接更紧密,从而有效提高了导电胶的导电性能和力学性能,解决了导电胶固化后易开裂、韧性不足等难题。