Quantitative evaluation of rubber/silica particle interphase through measurement of heat capacity.

摘要

The effectiveness of fillers to modify rubber composite properties depends on the particle size, the filler concentration, the filler distribution in the rubber, and the properties of the interphase, the layer of rubber next to the filler particle surface. Rubber molecules closest to the surface of a reinforcement particle are constrained by the presence of the particle surface. This reduced molecular mobility affects the properties of the interphase rubber. Many investigations have shed light on the nature of the interaction between rubber and filler surface. Many models have been proposed to describe the interaction rubber at the interphase but there has not yet been any direct measurement of interphase physical properties.;The present study employed three methods to quantitatively examine the physics of the interphase of the rubber and the filler: atomic force microscopy (AFM), thermal conductivity measurement, and heat capacity measurement. Initially, cured blends of natural rubber with various levels of carbon black filler were evaluated by AFM in an attempt to characterize the hardness and thickness of the interphase. Vulcanized samples were prepared by cryogenic ultramicrotomy for room-temperature AFM. This effort did not achieve its initial goal due to difficulties in preparing an appropriate sample surface to reveal the interphase for AFM. However, the AFM study did evolve into an MS thesis on independent nanoscale mechanical properties of incompatible rubber blend phases. Next, thermal conductivity measurements from 300 K to 2.9 K were made on cured styrene butadiene rubber (SBR) containing silica to characterize and model the impact of the interphase on heat transport and thereby, hopefully, to quantitatively evaluate silica particle dispersion. This effort did not achieve its initial goal since thermal conductivity values were too low to be measured with enough precision to differentiate among samples. Finally, on uncured samples of SBR containing silica, heat capacity versus temperature was successfully derived for the interphase rubber, separating it from the background rubber matrix.