A silicone rubber has linear thermal expansivity

PHYSICS · Multi-part · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Soft condensed matter · Soft condensed matter

Soft Matter at the Thermal Scale, Ch Rubber elasticity, swelling and gelation

Problem

A silicone rubber has linear thermal expansivity αL=3.0×10−4 K−1\alpha_L = 3.0\times10^{-4}\,\mathrm{K^{-1}}. Treat it as an ideal entropic network, with GG proportional to TT, held at fixed length near T=298 KT = 298\,\mathrm{K}. ((a)) Estimate the strain of thermoelastic inversion from the small-strain form of the inversion condition. ((b)) A strip of this rubber held at a strain of 55 per cent is warmed slightly. Does its tension rise or fall? What does a strip held at 1515 per cent do? ((c)) On the same model natural rubber, with αL≈2.2×10−4 K−1\alpha_L \approx 2.2\times10^{-4}\,\mathrm{K^{-1}}, inverts near 6.66.6 per cent. Which of the two rubbers must be stretched further before warming tightens it, and why?

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