Stretch-Induced Crystallization and Phase Transitions of Poly(dimethylsiloxane) at Low Temperatures: An in Situ Synchrotron Radiation Wide-Angle X-ray Scattering Study

摘要

Stretch-induced crystallization (SIC) and phase transitions of poly(dimethylsiloxane) (PDMS) have been studied with the in situ synchrotron radiation wide-angle X-ray scattering technique (WAXS) during tensile deformation at temperatures ranging from -45 to -65 degrees C. The phase transitions during tensile deformation go through different processes at different temperature regions, where four phases are involved in namely oriented amorphous (OA), mesophase, alpha form, and beta form crystals. We found that SIC of the alpha form can proceed via two different multistage ordering processes with either the mesophase or beta form as the structural intermediate. Further cyclic tensile experiments demonstrate that the transition from the beta to alpha form is a reversible process controlled by stress, which is attributed to the different helical pitches in beta and alpha forms. A nonequilibrium phase diagram of SIC and phase transitions are constructed in strain-temperature space, which is of great significance for practical applications of PDMS at low temperature.