Heat capacity, entropy and enthalpy of silicone-poly(styrene butadiene) rubber blends from 80 to 300 K

Abstract

Measurements of the variation of heat capacity, entropy and enthalpy of silicone and poly(styrene butadiene) rubber blends of composition 0–100%, 20–80%, 40–60%, 80-20% and 100-0% from 80 to 300 K are reported. It is observed that the heat capacities of blends have two clear anomalies which correspond to the glass transition temperature regions of silicone and styrene butadiene rubber (SBR). It is also found that the change of heat capacity with blend composition becomes reversed at around 200 K. The experimental values of heat capacity for the entire blend composition are empirically correlated by a single polynomial equation for the above temperature zone in the form: C( T) = A 1 T + A 2 T 2 − A 3 T 3 where the constants A 1, A 2, A 3 are functions of composition ( F). The values of the constants also change after 200 K when a reversal of the change of heat capacity with composition occurs. This empirical equation fits well with the experimental values throughout the range except in the transition regions. The change of entropy and enthalpy thus obtained from heat capacity are also correlated by a similar set of empirical equations of the form S or H = B 1 T + B 2 T 2 + B 3 T 3 + constant. These parameters also increase with temperature, with a sudden rise near the transition temperature of SBR only. The average standard deviation is found to be 5% maximum.