All-atom molecular dynamics simulation of structure, dynamics and mechanics of elastomeric polymer materials in a wide range of pressure and temperature†

Abstract

Rubber materials possess remarkable properties, rendering them indispensable in numerous sectors including national defense, military industry, healthcare and automotive tire manufacturing. Consequently, they hold significant importance as engineering materials. This study employs all-atom molecular dynamics simulation to comprehensively investigate the static and dynamic characteristics of pure rubber systems, rubber/SiO₂ nanocomposite systems and crosslinked rubber systems, focusing on natural rubber (NR), butadiene rubber (BR) and styrene–butadiene rubber (SBR) under varying pressure and temperature conditions. Our findings reveal a strongly positive correlation between the glass transition temperature (T_g) and pressure. It was observed that with every 100 atm increase in pressure, T_g experienced a rise of approximately 2–3 K. Moreover, the thermal expansion coefficient (TEC) of rubber systems in the glassy state is lower than that in the rubbery state and experiences reduction as pressure intensifies or with the introduction of SiO₂ nanoparticles and crosslinking. Additionally, the study investigates the P–V–T relationship and bulk modulus of diverse rubber systems, establishing that elevated pressure or reduced temperature leads to an enhancement in the isothermal bulk modulus. Further, as temperature escalates or pressure diminishes, the mean square displacement (MSD) of all the rubber systems displays an upward trend, indicative of augmented molecular chain mobility. However, the incorporation of SiO₂ nanoparticles or the implementation of crosslinking serves to impede the mobility of rubber chains. Evaluations of the mechanical properties of the rubber systems indicate that elevated temperature results in a reduction in the tensile strength. Notably, a comparison of the mechanical properties across different rubber systems demonstrates that NR exhibits the highest tensile strength, while BR exhibits the lowest. In conclusion, this work systematically explores the intricate interplay between the structure, dynamics and mechanics of distinct rubber materials induced by pressure and temperature, providing valuable theoretical guidance for the design and fabrication of rubber materials under extreme conditions.