Establishment of Constitutive Model of Silicone Rubber Foams Based on Statistical Theory of Rubber Elasticity

In this study, a constitutive model based on microscopic physical mechanism of silicone rubber foams was established. A theoretical statistical model of rubber elasticity considering the effect of dangling chains was modified to build this model. When a strain amplification factor （X） was introduced, the theoretical model could fit the tensile stress-strain data of mono- and bi-modal foam matrix well （Adj. R-Square = 0.9989, 0.9983）. Parameters related to the polymer network, namely, average molecular weight （Me） and volume fraction （Ф） of chain segments between adjacent cross-linking points （network strands）, were calculated by probabilistic method from the number-average molecular weight （Mn）, vinyl content （wvi） of the primary polysiloxanes and percent conversion （q） of vinyl groups. The primary and infinite strain amplification factors （X0, X∞） and decay exponent （z）, introduced by X and related to the nanoparticles, were obtained by fitting. Inspired by the fact that the actual strain of matrix was lower than that of the foams＇, we introduced another item, strain hysteresis item （H, related with the foam porosity and cell structure）, into the statistical model as well. With the same above values of Mc, Ф, X0 and X∞, the model could also fit the compressive stress-strain data of mono- and bi-modal foams well （Adj. R-Square = 0.9948, 0.9985）. Interestingly, the strain hysteresis items of the mono- and bi-modal foams almost completely coincided under all experimental strains, which may be attributed to the almost equal porosity and similar cell structure of the two foams. This constitutive model may connect the macroscopic stress-strain behaviour to the parameters of microscopic molecular structures, promisingly providing a basis for the performance improvement and optimization of silicone rubber foams.

Preparation and Properties of Conductive Foamed Silicone Rubber

The conductive foamed silicone rubber was prepared by Polymethylvinylsiloxane(PMVS)mixed with acetylene black,fumed silica,and AC foaming agent(azodicarbonamide).Influences of fillers on the microstructure,electrical conductivity and mechanical property were discussed.The results showed that the pore structure was affected by acetylene black.Acetylene black delayed the vulcanization speed of silicone rubbers,leading to bigger pores.Higher content of acetylene black decreased the mechanical properties and the electrical resistivity of rubbers.Fumed silica increased the mechanical properties and limited the aggregation of gas.Higher content of fumed silica led to small and obturator pores generated.Higher content of fumed silica increase the mechanical properties and the electrical resistivity of rubbers.AC foaming agents generated more gas,leading to bigger and irregular pores which affected the mechanical properties negatively,meanwhile AC foaming agents increased the conductivity of rubbers.