As skirt and shed materials of outdoor insulators, silicon dioxide (SiO₂) filled polydimethylsiloxane (PDMS) sometimes have to work under extremely cold environment, which can induce crystallization inside the PDMS composites. Herein, differential scanning calorimeter (DSC) is combined with X-ray diffractometer (XRD) to investigate the crystal structures of PDMS composites after non-isothermal crystallization and isothermal crystallization at -60°C. The dielectric properties of SiO₂ filled PDMS are further measured. DSC and XRD results indicate that the crystals size is larger and crystal spacing is denser for non-isothermal crystallization than those for isothermal crystallization, which may be due to the few small crystal nucleus and enhanced mobility of chains at relatively high isothermal crystallization temperature. Compared to isothermal crystallization, the dielectric relaxations magnitude of rigid amorphous fraction caused by molecules chains restrained in crystals is less and relaxations corresponding to mobile amorphous fraction is more concentrated, which is due to the more stable crystal structures after non-isothermal crystallization.

Crystal structures,isothermal crystallization,non-isothermal crystallization,polydimethylsiloxane,Dielectric properties