Progress in preparation, processing and applications of polyaniline

Intrinsic strain softening appears to be the main cause for the occurrence of plastic localization phenomena in deformation of glassy polymers. This is supported by the homogeneous plastic deformation behavior that is observed in polycarbonate samples that have been mechanically pretreated to remove (saturate) the strain softening effect. In this study, some experimental results are presented and a numerical analysis is performed simulating the effect of mechanical conditioning by cyclic torsion on the subsequent deformation of polycarbonate. To facilitate the numerical analysis of the mechanical rejuvenation effect, a previously developed model, the compressible Leonov model, is extended to describe the phenomenological aspects of the large strain mechanical behavior of glassy polymers. The model covers common observable features, like strain rate, temperature and pressure dependent yield, and the subsequent strain softening and strain-hardening phenomena. The model, as presented in this study, is purely single mode' (i.e., only one relaxation time is involved), and therefore it is not possible to capture the nonlinear viscoelastic pre-yield behavior accurately. The attention is particularly focused on the large strain phenomena. From the simulations it becomes clear that the preconditioning treatment removes the intrinsic softening effect, which leads to a more stable mode of deformation.

The Influence of Intrinsic Strain Softening on Strain Localization in Polycarbonate: Modeling and Experimental Validation

Chemically modified graphene sheets were dispersed in a high-performance polyimide (PI) matrix using polyamic acid (PAA)/graphene nanocomposite as a precursor. PI nanocomposite films with different loadings of graphene sheets were prepared by thermal imidization of the as-prepared PAA/graphene nanocomposites. Graphene oxide (GO) synthesized by Hummer’s method was chemically reduced with various reducing agents to produce reduced GOs (rGOs). The incorporation of only 5 wt % GO resulted in an ∼12-fold and ∼18-fold increase in the tensile strength and tensile modulus of PI, respectively, while the PI/rGO nanocomposites were found to have relatively inferior tensile properties. The superior mechanical properties of the PI/GO nanocomposites were attributed to the good dispersion and effective stress transfer between the polymer and GO sheets, as evidenced by the results from X-ray diffraction (XRD) and morphological studies. Furthermore, the PI/GO nanocomposites exhibited higher loading capacity than PI/rGO. T...

Effect of chemical modification of graphene on mechanical, electrical, and thermal properties of polyimide/graphene nanocomposites.

The effect of coupling agent on electrical and mechanical properties of carbon fiber/phenolic resin composites

Electronic Properties of Materials

Physical properties of polystyrene/alum composites

Ac electrical properties of aluminium flakes–epoxy composites were studied as a function of the composition, frequency and temperature The dielectric constant increased smoothly with an increase in the concentration of aluminium An increase in the dielectric constant was observed with the temperature as well as with a decrease in the frequency The observed increase in the values of the dielectric constant with the aluminium concentration was attributed to interfacial polarization It was found that ac electrical conductivity increases with increasing content of aluminium, temperature and frequency The observed enhancement in ac conductivity is attributed to the increase in the number of conduction paths created by the aluminium flake contacts in the composite to give a higher electrical conductivity Also, the activation energy of aluminium flakes–epoxy composites was determined, as well as the values of the dielectric constant Compared with various theoretical models, Bruggman's formula gives a better fit The universal power-law model of ac conductivity is observed in epoxy–aluminium composites The calculated power exponent (about unity) is physically acceptable within this applied model

https://iopscience.iop.org/article/10.1088/0022-3727/41/16/165408/pdf

Study of ac electrical properties of aluminium–epoxy composites

The yielding and crazing behaviour of polycarbonate in torsion under superposed hydrostatic pressure

The electrical and thermal properties of thin films of polyimide/silica nanocomposites prepared via sol–gel process were studied as a function of nanosilica particles content, temperature and applied field frequency. It was found that the dielectric constant and dielectric loss of the nanocomposites decrease with both the frequency and the nanosilica content, while increase with temperature. The AC-conductivity measured in frequency range 200 kHz–1.5 MHz decreases with the filler concentration and increases with increasing temperature. For the (25 wt%) nanocomposite, it was found that the AC-conductivity increases with temperature, and the Cole–Cole plots showed that the calculated activation energy and relaxation time decrease with temperature. The observed thermal conductivity increases gently with temperature. The empirical universal law was used to fit the observed electrical data under the measuring conditions.

https://www.tandfonline.com/doi/pdf/10.1080/17458080.2010.547950

Electrical and thermal properties of polyimide/silica nanocomposite

The optical properties of thin films of polyimide/silica nanocomposites prepared via sol–gel process were investigated as a function of nanosilica particles content. Absorption and reflectance spectra were collected by a spectrophotometer giving UV-radiation of wavelength range 200–800 nm. The optical data obtained were analyzed in terms of absorption formula for non-crystalline materials. The calculated values of the optical energy gap and the width of the energy tails of the localized states exhibited silica concentration dependence. The direct optical energy gap for neat polyimide is about 1.95 eV, and decreases to a value of 1.8 eV for nanocomposite of 25 wt% nanosilica content. It was found that the calculated refractive index and dielectric constants of nanocomposites increase with silica particles content. The overall dependence of the optical and dielectrical constants on silica content in polyimide matrix is argued on the basis of the observed morphology and overlap of the localized energy sates of different color centers. The EMT model was fitted to the observed dielectric data.

A. M. Zihlif

Papers

Physical properties of polystyrene/alum composites

Study of ac electrical properties of aluminium–epoxy composites

The yielding and crazing behaviour of polycarbonate in torsion under superposed hydrostatic pressure

Electrical and thermal properties of polyimide/silica nanocomposite

Optical properties of polyimide/silica nanocomposite