Molecular dynamics simulation of glass transition and thermal stability of novel silicone elastomer and its nanocomposites

Existing silicone elastomers (SR) are difficult to serve properly in extreme high and low temperature environ-ments. Herein, through molecular dynamics (MD) simulations, a novel SR with wide temperature resistance range was designed using silicon-oxygen bonds (-Si-O-) to construct the backbone and side chains of polymer chains. Firstly, we investigated the cold and heat resistance of SR with various grafting density and side chain length. Three different approaches were utilized to estimate the glass transition temperature (Tg) of SR, i.e., by calculating the volume, non-bonding energy, and conformational transitions rate of the torsion angle (KT). Also, the rate of change of mean square displacement (MSD) versus temperature was used to characterize the thermal decomposition temperature (Td) of this designed material. The results demonstrated that when the grafting density is high and the length of side chain is moderate, the elastomer has the best extreme temperature resis-tance, with Tg and Td reaching below -140 degrees C and above 420 degrees C respectively. Then, SR pyrolysis was inves-tigated by Reactive Force Field (ReaxFF) MD simulations. The dominant final products were CH4, H2, C2H4 and siloxane. Finally, the introduction of SiO2 nanoparticles improves the cold and heat resistance of the composite, with Tg reaching about -150 degrees C and Td reaching above 450 degrees C. In addition, the heterogeneous distribution of molecular chain conformational transitions demonstrated that the introduction of more nanoparticles resulted in the chain segments have more space for rotation, leading to decrease in Tg. Arrhenius parameters were extracted through pyrolysis simulations, illustrating that the SiO2 nanoparticles improves the thermal stability of nano -composites. In general, our work could provide rational guidelines for the design and fabrication of novel polymeric materials with a wide temperature resistance range.