Thin and high conductive multi-walled carbon nanotubes/polydimethylsiloxane composite film prepared via solvent method as strain sensors

Flexible strain sensors based on conductive fillers and flexible polymers possessed significant advantages in human motion detection. Preparing a strain sensing layer with high electrical conductivity and excellent mechanical property under high content of conductive filler contributed to the stability of flexible strain sensors. In this study, MWCNTs/PDMS composite film was prepared by the organic solvent method. The microstructure, electrical conductivity, mechanical property, and piezoresistive characteristics of the composite film at different MWCNTs contents were characterized and discussed. When the mass fraction of MWCNTs in the composite film was 5%, the composite film exhibited a high electrical conductivity of 9.56 S/m while maintaining ideal mechanical properties, and the film thickness was just about 180 μm. The relationship between electrical signals and film strain was performed. The piezoresistive characteristic results demonstrated that the prepared composite film could be used as flexible strain sensor for human motion detection. The prepared thin MWCNTs/PDMS composite film in this paper illustrated high conductive and desired flexibility, and was an alternative material for human motion detection.     

Synthesis of a hexafluoropropylidene-bis(phthalic anhydride)-based polyimide and its conducting polymer composites with polypyrrole

A new electrically conducting composite film from polypyrrole and 4,4′-(hexafluoroisopropylidene)-bis(phthalic anhydride)-based polyimide was prepared. Pyrrole and the dopant ion can easily penetrate through the polyimide substrate and electropolymerize on the platinum (Pt) electrode due to the swelling of the polyimide on the metal electrode. The electrochemical properties of polypyrrole-polyimide (PPy/PI) composite films have been investigated by using cyclic voltammetry. The PPy/PI composite film is suitable for use as the electroactive material owing to its stable and controllable electrochemical properties. The electrical conductivity of composites falls in the range 0.0035–15 S/cm. Scanning electron micrograph, FTIR, and thermal studies indicate that PPy and PI form a homogeneous material rather than a simple mixture. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3009–3016, 1997     

聚吡咯(PPY)/聚己内酰胺(Nylon 6)——导电复合材料的研究

本文用电化学氧化聚合的方法制备出了既具有优良的导电性能又具有良好机械性能的聚吡咯(PPY)/聚己内酰胺(Nylon 6)的复合材料,该复合材料的导电率可达119s/cm,并对聚吡咯/聚己内酰胺导电复合材料进行了扫描电子显微镜、电导率及机械性能的测试及表征。     

基于多层结构设计的高储能密度氧化石墨烯/聚酰亚胺复合材料

采用逐层涂布、 分层控制固化程度的方法, 利用聚酰胺酸(PAA, 聚酰亚胺前体)溶液和含有氧化石墨烯（GO）的PAA溶液制备了一系列由高绝缘性PI层与GO@PI介电层交替组合而成的界面清晰且紧密衔接的多层复合薄膜. 通过调控介电层中GO含量及分层结构, 使多层复合薄膜兼具高介电常数和高击穿强度特征. 结果表明, 三层复合薄膜PI/1.0GO@PI/PI的击穿强度为261.5 kV/mm, 储能密度达到1.27 J/cm³, 与相同介电层厚度的单层薄膜相比, 击穿强度和储能密度分别提高了97%和144%, 同时, 其介电损耗也保持在较低水平(tanδ=0.0079). 绝缘层和高介电常数层的协同作用提升了氧化石墨烯/聚酰亚胺复合薄膜的储能密度. 这种简单的多层结构设计有利于氧化石墨烯/聚合物复合材料在介质储能领域的应用.     

High modulus polyimide/polyimide molecular composite films that utilize acetylene unit as a crosslink site

Polyimide/polyimide molecular composite (MC) films comprised of a rigid polyimide derived from biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) and a flexible polyimide derived from BPDA and bis (3,3'-diaminodiphenyl) acetylene (intA) and/or oxydianiline (ODA) were prepared by blending the polyamic acid solutions in 7 : 3 weight ratio, and then imidizing the blend films. Acetylene content in the flexible polyimide backbone was controlled by the ratio of intA and ODA. Cold-drawing of the blend polyamic acid films, followed by imidization, gives high modulus polyimide/polyimide MC films. The modulus of the MC films increased almost linearly with the draw ratio, reaching 25.5 GPa for the 40% drawn film. Acetylene groups in the flexible polyimide can be thermally cured to crosslink. The onset of exotherm appeared at 340°C on DSC, reaching maximum at 398°C. After the thermal crosslinking, the MC films maintained the high modulus, though elongation became small. Taking advantage of the crosslinkable acetylene units, two MC films were laminated and processed at 400°C for 20 min under 100 kg/cm² to give a good-quality laminate film. The interface of the two films was strongly bonded through the crosslinking of acetylene groups. Laminate films maintained the high modulus afforded by the cold-drawing. © 1994 John Wiley & Sons, Inc.     

Electrochemically polymerised composites of multi-walled carbon nanotubes and poly(vinylferrocene) and their use as modified electrodes: application to glucose sensing

We report electrochemical composites of multi-walled carbon nanotubes (MWCNTs) with poly(vinylferrocene) (PVF). The polymeric architecture is prepared by first immobilising the MWCNTs onto a glassy carbon substrate, which acts to introduce electrical current into the composite, with the MWCNTs acting as 'molecular wires'. PVF films of varying surface coverages can be obtained by simply controlling the time a constant potential of +0.7 V (vs. Ag) wire is applied; with the characteristics of the derivatised MWCNTs examined by cyclic voltammetry and scanning electron microscopy.The application of the composite for glucose determination in aqueous solutions was investigated using linear sweep voltammetry, where it was found that the composites supported on glassy carbon substrates are superior to bare glassy carbon electrodes polymerised with PVF, likely due to the comparatively higher number of electrocatalytic centres in the former. This protocol was successfully transferred to prepare a PVF-MWCNT-paste electrode which was applied to glucose detection in diluted laked horse blood. The obtained results show potential and promising practical application for the polymer-derivatised MWCNT-modified electrodes in amperometric sensors for glucose determination.     

Preparation of ultrathin films of aromatic polymides by vapor deposition polymerization from N-silylated aromatic diamines or aromatic tetracarboxylic dithioanhydride

A novel method for the preparation of ultrathin films of aromatic polyimides was developed through vapor deposition polymerization from combinations of monomer pairs of either N,N′-bis (trimethylsilyl)-substituted aromatic diamines and pyromellitic dianhydride or aromatic diamines and pyromellitic dithioanhydride. Both diamine component and tetracarboxylic dianhydride component were evaporated simultaneously at a stoichiometric molar ratio under vacuum, giving a deposited film on a substrate, which consisted of a polyamic acid derivative formed by the ring-opening polyaddition. The deposit was then converted to polyimide by thermal imidization at a relatively lower temperature, compared with a conventional method using the parent diamine and tetracarboxylic dianhydride. The properties of polyimide ultrathin films such as thermal stability, chemical resistance, and dielectric behavior were almost the same as those of the polyimide films prepared by a conventional method.     

A Nitrite Biosensor Based on the Direct Electron Transfer of Hemoglobin Immobilized on Carboxyl‐Functionalized Multiwalled Carbon Nanotubes/Polyimide Composite

The high electrically conductive carboxyl‐functionalized multiwalled carbon nanotubes (COOH‐MWCNTs) were used to combine with nonconducting polyimide (PI) to generate a PI/COOH‐MWCNTs membrane. PI served as a matrix to entrap COOH‐MWCNTs and hemoglobin (Hb). COOH‐MWCNTs can improve the conductivity of the composite. The direct electrochemistry measurement indicated that the PI/COOH‐MWCNTs composite enhanced the immobilization of Hb significantly. Besides, the Hb/PI/COOH‐MWCNTs/GCE biosensor possessed excellent electrocatalytic activity for the detection of nitrite. Therefore, PI is a good matrix for Hb immobilization and it has application in sensor construction. This work is promising in the development of sensitive biosensors based on PI/COOH‐MWCNTs composite film.     

Poly(ether‐imide) and related sepiolite nanocomposites: investigation of physical,thermal, and mechanical properties

Novel poly(ether‐imide) and sepiolite nanocomposites were synthesized based on a unique diamine monomer with the aim of improving physical and mechanical properties of final polyimide films. The diamine was polycondensed with 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride to produce related poly(ether amic acid) prepolymer. Pure poly(ether‐imide) and nanocomposite films were prepared via thermal imidization process of poly(ether amic acid). Coexistence of ether, pyridine, and phenylene functional groups in the diamine chemical structure resulted in flexible polyimide films with significant thermal, physical, and mechanical properties. Thermal stability, glass‐transition temperature, dimensional stability, and tensile properties of polymer and nanocomposites were studied and compared. Morphology of nanocomposites was also investigated using scanning and transmission electron microscopic methods to study the distribution and dispersion behavior of sepiolite nanofibers in the polyimide matrix. By introduction of sepiolite nanoparticles, overall improvement of properties was observed in respect to pure polyimides. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced toughness and strength of conductive cellulose-poly(butylene succinate) films filled with multiwalled carbon nanotubes

Cellulose (CE) composite films with high tensile strength, modulus, remarkable elongation as well as excellent electrical conductivity were successfully prepared by dispersing poly(butylene succinate) (PBS) and multiwalled carbon nanotubes (MWCNTs) in CE matrix via the help of ionic liquid 1-allyl-3-methylimidazolium chloride. Fourier transform infrared spectroscopy and differential scanning calorimetry results verified that a physical interaction junction existed between PBS and CE. Scanning electron micrograph (SEM) showed that the low content PBS was uniformly dispersed in CE matrix, leading to a tough and ductile fractured surface. The elongation at break of CE composite film with 1 wt% PBS was increased to 25.9 %, which showed an increase of 325 % compared to that of neat CE film (6.07 %). But high-content PBS acted as the structural defect in the CE matrix. MWCNTs were further added to improve the mechanical and conductive properties of the composite film. The tensile strength and Young’s modulus of MWCNT/CE-PBS composite film with 4 wt% MWCNTs were respectively increased by 33.6 and 140 % compared to CE-PBS film. The electrical conductivity of MWCNT/CE-PBS film was also improved by 8–9 orders of magnitude from 2.5 × 10^?14 to 1.3 × 10^?5 S/m.     

Simultaneous determination of adenine guanine and thymine at multi-walled carbon nanotubes incorporated with poly(new fuchsin) composite film

A composite film (MWCNTs-PNF) which contains multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(new fuchsin) (PNF) has been synthesized on glassy carbon electrode (GCE), gold (Au) and indium tin oxide (ITO) by potentiostatic methods. The presence of MWCNTs in the composite film enhances surface coverage concentration (Γ) of PNF to ≈176.5%, and increases the electron transfer rate constant (k_s) to ≈346%. The composite film also exhibits promising enhanced electrocatalytic activity towards the mixture of biochemical compounds such as adenine (AD), guanine (GU) and thymine (THY). The surface morphology of the composite film deposited on ITO has been studied using scanning electron microscopy and atomic force microscopy. These two techniques reveal that the PNF incorporated on MWCNTs. Electrochemical quartz crystal microbalance study reveals the enhancement in the functional properties of MWCNTs and PNF. The electrocatalytic responses of analytes at MWCNTs and MWCNTs-PNF films were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electrocatalysis studies, well separated voltammetric peaks have been obtained at the composite film for AD, GU and THY, with the peak separation of 320.3 and 132.7 mV between GU-AD and AD-THY respectively. The sensitivity of the composite film towards AD, GU and THY in DPV technique is 218.18, 12.62 and 78.22 mA M⁻¹ cm⁻² respectively, which are higher than MWCNTs film. Further, electroanalytical studies of AD, GU and THY present in single-strand deoxyribonucleic acid (ssDNA) have been carried out using semi-derivative CV and DPV.     

ELECTRICALLY CONDUCTIVE COMPOSITE PREPARED BY ELECTROCHEMICAL POLYMERIZATION OF PYRROLE IN POLY-(p- PHENYLENE TEREPHTHALAMIDE) MATRIX

The preparation of PPy/PPTA conductive composite films by electrochemical method is presented.The first step is to cast a thin layer of poly (p-phenylene-terephthalamide) (PPTA) on a slice of Pt working electrode. The second step is to electrochemically polymerize pyrrole on the PPTA/Pt working electrode. Both of the electrical conductivity and the mechanical properties of the PPy/PPTA composite film are better than those of the pure PPy film, and the film has excellent flexibility at low temperature, even in liquid nitrogen.The SEM picture of the cross-section of PPy,/PPTA composite film showed that the two components were well mixed.Cyclic voltammograms of PPy,/PPTA film in aqueous solution showed that the conductive films could be reduced and reoxidized.     

Poly(malachite green) at nafion doped multi-walled carbon nanotube composite film for simple aliphatic alcohols sensor

Conductive composite film which contains nafion (NF) doped multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(malachite green) (PMG) has been synthesized on glassy carbon electrode (GCE), gold and indium tin oxide (ITO) electrodes by potentiostatic methods. The presence of MWCNTs in the composite film (MWCNTs-NF-PMG) enhances surface coverage concentration (Γ) of PMG to ≈396%, and increases the electron transfer rate constant (k_s) to ≈305%. Similarly, electrochemical quartz crystal microbalance study reveals the enhancement in the deposition of PMG at MWCNTs-NF film. The surface morphology of the composite film deposited on ITO electrode has been studied using scanning electron microscopy (SEM) and scanning tunneling microscopy (STM). These two techniques reveal that the PMG incorporated on MWCNTs-NF film. The MWCNTs-NF-PMG composite film also exhibits promising enhanced electrocatalytic activity towards the simple aliphatic alcohols such as methanol, ethanol and propanol. The electroanalytical responses of analytes at NF-PMG and MWCNTs-NF-PMG films were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). From electroanalytical studies, well defined voltammetric peaks have been obtained at MWCNTs-NF-PMG composite film for methanol, ethanol and propanol at Epa = 609, 614 and 602 mV respectively. The sensitivity of MWCNTs-NF-PMG composite film towards methanol, ethanol and propanol in CV technique are 0.59, 0.36 and 0.92 μA mM⁻¹ cm⁻² respectively, which are higher than NF-PMG film. Further, the sensitivity values obtained using DPV are higher than the values obtained using CV technique.     

Structure and infrared emissivity of polyimide/mesoporous silica composite films

Polyimide/mesoporous silica composite films were prepared by direct mixing of polyamic acid solution and silylated mesoporous silica particles, or by condensation polymerization of dianhydride and diamine with silylated mesoporous silica particles in N,N-dimethylacetamide, followed with thermal imidization. Structure and glass transition temperatures of the composite films were measured with FTIR, SEM, EDX, XPS and DMTA. The results show that the silylated mesoporous silica particles in the composites tend to form the aggregation with a strip shape due to phase separation. The composite films exhibit higher glass transition temperature as comparing with that of pure polyimide. It is found that the composite films present lower infrared emissivity value than the pure polyimide and the magnitude of infrared emissivity value is related to the content of silylated mesoporous silica in the composite films. Inhibiting actions of silylated mesoporous silica on infrared emission of the composite films may be owing to presence of nanometer-scale pores in silylated mesoporous silica.     

High performance polymer films 4. Mechanical behavior

Tensile properties of the polyimide and copolyimide films based on two dianhydrides, pyromellitic dianhydride (PMDA) and 3,3^′,4,4^′-benzophenonetetracarboxylic dianhydride (BTDA) and two diamines, 4,4^′-oxydianiline (ODA), and a proprietary aromatic diamine (PD) have been described. The tensile strength of the films containing higher proportions of BTDA or PMDA and PD is much higher (except the fully rigid film based on PMDA-PD which is brittle in nature) than the films containing higher proportion of ODA moiety. The films containing PD as the diamine moiety exhibit high initial moduli than the films containing exclusively or mainly ODA as the diamine moiety. The films having higher concentration of the -O- linkage originated from diamine ODA are found to exhibit higher elongation values. There is found to be no direct correlation between η_inh of the precursor casting solutions and mechanical properties of structurally different polyimide/copolyimide films. For a particular polyimide or copolyimide film, the tensile strength value is found to be less sensitive than the elongation to the variation of η_inh value of the precursor poly(amic acid) or copoly(amic acid). Tensile strength and elongation of the film, basically rigid in nature, may be improved by post-curing at 360°C/370°C. While Kapton H film retains 78% and 63.5% of its tensile strength and % elongation at break (% E_b) respectively after hot-wet mechanical test, the film based on BTDA 80, PMDA 20 and PD shows an increase of about 27% and 22% in its tensile strength and % E_b respectively.     

Preparation and characterization of electrostrictive polyurethane films with conductive polymer electrodes

All-polymer electrostrictive soft films were developed for the first time by depositing conductive polymer (polypyrrole) directly on both sides of solution-cast electrostrictive polyurethane elastomer films. The final composite films are flexible with strong adhesion between the polyurethane film and the conductive polymer electrode. The conductivity (sheet resistivity ∼1000 Ω/□), of the polymer electrode is appropriate for its intended use. The compatible interface between the polypyrrole electrode polymer and the electrostrictive polyurethane significantly improves the acoustic and optical transparency of these composite films, compared with using a metal electrode film. The all-polymer films also exhibit comparable dielectric properties to gold-electroded polyurethane films in the temperature range from −40^°C to +80^°C. The temperature range covers the soft segment glass transition temperature of the polyurethane elastomers, which is about −20^°C. The films also show large electric field induced strain responses which are dependent on film thickness and measurement frequency. The electrostrictive characteristics in the all-polymer films show similarities to those of the films with gold electrodes under identical measurement conditions. © 1998 John Wiley & Sons, Ltd.     

水溶性多壁碳纳米管/铜酞菁染料自组装薄膜的制备与表征

Water soluble multi-wall carbon nanotubes (MWCNTs) were prepared via chemical oxidation. Under ultrasonication,the chemically treated MWCNTs can be dispersed in water to form colloids. The MWCNTs were characterized by FT-IR spectra. The FT-IR spectra reveal the presence of carboxylic groups on the nanotubes. The functional groups can improve the nanotubes-solubility in water. Alcian Blue 8GX (AB), a quaternary ammonium dye of the copper phthalocyanine group, was dissolved in water and used to form electrostaticcally self-assembled multilayer films. The MWCNT/AB composite films were characterized by UV-vis absorption spectra as well as AFM and fluorescence spectrum. The experimental results show that the MWCNT/AB composite films can be produced easily. Compared to those of the AB aqueous solutions, composite films exhibit pronounced differences in the absorption and fluorescence spectra, which suggests that AB molecules aggregated in the composite film, and that a charge transfer might exist between AB molecules and the MWCNTs.     

Dissolution of MWCNTs by using polyoxadiazoles,and highly effective reinforcement of their composite films

Nonmodified multiwalled carbon nanotubes (MWCNTs)/sulfonated polyoxadiazole (sPOD) nanocomposites are successfully prepared by a facile solution route. The pristine MWCNTs are dispersed in a sPOD solution, and the mixtures are fabricated into thin films by solution casting. The homogeneous dispersion of nanotubes in the composites is confirmed by transmission electron microscopy. The mechanical properties, thermal stability, and electrical conductivity are investigated. Tensile strength, elongation at break, and tensile energy to break are shown to increase by more than 28, 45, and 73%, respectively, by incorporating up to 1.0 wt % pristine MWCNTs. The experimental values for sPOD/MWCNTs composite stiffness are compared with Halpin‐Tsai and modified Halpin‐Tsai predictions. The storage modulus is found to increase up to 10% at low CNT loading. The composite films, which have an outstanding thermal stability, show an increase of up to 57 °C in the initial degradation temperature. The addition of 1.0 wt % MWCNTs increases the electrical conductivity of the sPOD matrix by two orders of magnitude. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

镧掺杂的二氧化锰/碳纳米管电化学超级电容器复合电极

尽管在二氧化锰/多壁碳纳米管（MnO₂/MWCNTs）上获得了较高的比电容,低电导率仍是制约MnO₂担载量或膜厚度提高的主要障碍.另一个问题是MnO₂/MWCNTs的循环稳定性远低于活性炭.所以截止到目前这一新型材料的应用仍然受到很大的限制.本文采用原位还原的方法制备镧掺杂二氧化锰/多壁碳纳米管电化学超级电容器复合电极材料.分别通过透射电镜（TEM）、扫描电镜（SEM）、X射线衍射（XRD）和傅里叶变换红外（FTIR）光谱等技术对这些复合材料的形貌与结构进行了分析.采用循环伏安法、恒电流充放电法和交流阻抗法对其进行了电化学性能的研究.研究结果表明,通过还原MnO₄^-可以在MWCNTs上形成La掺杂MnO₂复合材料.La掺杂降低了复合电极的电阻,这是因为La的引入可以增大MnO₂的晶格缺陷,从而提高材料的电导率以及电极的电化学性能.因此La掺杂是克服MnO₂本征导电性差的有效途径之一.掺杂La可以在不增大电极电阻的情况下提高MnO₂的担载量或膜厚度.La掺杂的更重要的作用是使以MnO₂/MWCNTs作电极的对称电化学超级电容器的循环性能得到显著改善.此外,La掺杂也使复合电极的比电容得到一定程度的提高.     

Layer-by-layer engineered Co-Al hydroxide nanosheets/graphene multilayer films as flexible electrode for supercapacitor

Multilayer films of Co-Al layered double hydroxide nanosheets (Co-Al LDH-NS) and graphene oxide (GO) were fabricated through layer-by-layer (LBL) assembly. By using a three-electrode system, the electrochemical performances of the films were investigated to evaluate their potential as electrode materials to be used in flexible supercapacitor devices. The Co-Al LDH-NS/GO multilayer films exhibited a high specific capacitance of 880 F/g and area capacitance of 70 F/m(2) under the scan rate of 5 mV/s. And the film exhibited good cycle stability over 2000 cycles. After treating the films at 200 °C in H(2) atmosphere, the specific capacitance and area capacitance were largely increased up to 1204 F/g and 90 F/m(2) due to partial reduction of GO. A flexible electrode by depositing Co-Al LDH-NS/GO multilayer film onto PET substrate was prepared to show the potential of Co-Al LDH-NS/GO films for flexible energy storage.