Molecular simulations of polyisoprene (PI) elastomers: study of microstructures and networks

Next generation elastomers in automobile industry aim to design materials that can lower the fuel costs being sustainable as well as meet rigorous safety standards. Current efforts in this field focus on leveraging computational methods for materials discovery to streamline and accelerate the design process. With the help of simulations and predictive modeling, researchers can efficiently identify promising elastomer formulations, significantly cutting down on the time and resources utilized in experiments. Polyisoprene (PI) is one such elastomer which is a critical component in modern elastomers as well as a model polymer that is used to describe fundamental aspects of polymer physics. This work focuses on probing the microscopic details of chemistry by developing detailed all-atom models to relate to the macroscopic properties and also inform coarser model that can probe properties over wider range of spatio-temporal scales. It is well known that 1,4-trans PI is more extended and has more intermolecular neighbors in comparison to 1,4-cis PI which is more flexible. It is hypothesized that trans PI has slower chain translation due to the higher number of neighboring chains but has faster local dynamics. Several probes were employed to inform that indeed this is true for lower molecular weight samples that can be tested through all-atom models. A simpler coarse-grain model was developed to extend the model to higher molecular weights where additional topological constraints such as entanglements have shown significant slowing down of the dynamics. Deviations from theoretical models were observed that could be attributed to the details of chemistry in polymers implying the need for refining to account for the intricate details of the microstructure. In another thrust using atomistic model, crosslinking of PI networks is explored highlighting the differences in mechanical properties due to location and length of the crosslink introduced. Overall, the aim of this work is to develop holistic models accounting for the specific details of chemistry in PI that can be used to explore new materials design for modern elastomers.