The effect of nanosized silica particles on the properties of poly(vinyl acetate) (PVAc) was investigated for a range of silica concentrations encompassing the percolation threshold. The quantity of polymer adsorbed to the particles ("bound rubber") increased systematically with silica content and was roughly equal to the quantity shielded from shear stresses ("occluded rubber"). This bound and occluded polymer attained a level of ∼12% at a silica volume content of 28%; nevertheless, the glass transition properties of the PVAc, including the glass transition temperature, local segmental relaxation function and relaxation times, and the changes in thermal expansion coefficient and heat capacity at T g , were unaffected by the interfacial material. That is, there is no indication that the local segmental dynamics of the chains adjacent to silica particles differ from the motions of the bulk chains. Interestingly, the volume sensitivity of the segmental dynamics, as determined from the scaling exponent γ in the relation T g ∼ V g -γ in which V g is the specific volume at the glass transition, becomes stronger with increasing silica concentration. Moreover, this dependence of γ increases abruptly at the filler percolation threshold. The implication of this result and possible directions for new research are considered.

We investigate the electrical properties of composite materials prepared as nano-and sub-micron-scale metal-oxide particles embedded in a commercial resin. The filler particles are barium titanate and calcium copper titanate. The physical and structural characteristics of the constituents and the fabricated composites are reported. Electrical characterization of the composite samples is performed using time-and frequency-domain dielectric spectroscopy techniques. The electrical breakdown strength of samples with nano-and sub-micron-sized particles have better electrical insulation properties than the unfilled resin.

In this paper, we report the dielectric breakdown properties of a nanocomposite, a potential electrical insulation material for cryogenic high voltage applications. The material is composed of a high molecular weight polyvinyl alcohol and nanosized in situ synthesized titanate particles. The dielectric breakdown strengths of the filled material samples, measured in liquid nitrogen, indicate a significant increase in their strengths as compared to unfilled polyvinyl alcohol. We conclude that nanometre-sized particles can be adopted as a voltage stabilization additive.

The longitudinal relaxation time tau of a series of alkyl-isothiocyanato-biphenyls (nBT) liquid crystals in the smectic E phase was measured as a function of temperature T and pressure P using dielectric spectroscopy. This relaxation time was found to become essentially constant, independent of T and P, at both the clearing point and the lower temperature crystalline transition. tau(T,P) could also be superposed as a function of the product TV(gamma), where V is the specific volume and gamma is a material constant. It then follows from the invariance of the relaxation time at the transition that the exponent gamma superposing tau(T,V) can be identified with the thermodynamic ratio Gamma=- partial differential log(T(c)) partial differential log(V(c)), where the subscript c denotes the value at the phase transition. Analysis of literature data on other liquid crystals shows that they likewise exhibit a constant tau at their phase transitions. Thus, there is a surprising relationship between the thermodynamic conditions defining the stability limits of a liquid crystalline phase and the dynamic properties reflected in the magnitude of the longitudinal relaxation time.

In this paper, we investigate the dielectric breakdown data of some insulating materials and focus on the applicability of the two- and three-parameter Weibull distributions. A new distribution function is also proposed. In order to assess the model distribution's trustworthiness, we employ the Monte Carlo technique and, randomly selecting data-subsets from the whole dielectric breakdown data, determine whether the selected probability functions accurately describe the breakdown data. The utility and strength of the proposed expression are illustrated distinctly by the numerical procedure. The proposed expression is shown to be a valuable alternative to the Weibull ones.

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