Thermodynamic investigation on melting and recrystallization of poly(dimethylsiloxane) rubbers under strain

Abstract

In order to clarify the melting and crystallization properties of poly(dimethylsiloxane) (PDMS) rubbers under strain, heat capacity measurements were conducted for stretched PDMS rubbers by adiabatic calorimetry in the temperature range 78–300 K. Upon stretching to the elongation ratio of 2.56, the fusion temperature T fus increased by 4 K, the fusion peak in heat capacity broadened, and the enthalpy of fusion Δ fus H increased by 3.6%. The increase in Δ fus H was due to the change of internal energy both in the rubbery and crystalline state. The increase in T fus was related to these changes in internal energy and the decrease in conformational entropy in the rubbery state. Broadening of the fusion peak indicated the wider distribution of crystal size. The measurements of the samples recrystallized at different temperatures revealed that the crystal thickening ratio and recrystallization kinetic rate increased with stretching ratios. • Fusion temperature of PDMS rubber increases under strain. • Enthalpy of fusion Δ fus H increases under strain due to the change of internal energy both in the rubbery and crystalline state. • Crystal thickening ratio and recrystallization rate increase with stretching ratios.