Understanding Permeability of Air/O2/N2 Through Different Rubbers Using Molecular Dynamics Simulations

Air barrier is an important property required for tyre inner-liners in tubeless tyres and in the tubes of the tube tyres used in passenger car types, trucks, buses, two or three-wheelers, etc. Isobutylene-isoprene rubber (IIR), and their halogen derivatives, brominated and chlorinated isobutylene-isoprene; (BIIR and CIIR) are generally used for tyre inner liners and in tubes due to their ability to maintain superior air retention, ensuring prolonged optimal tyre performance and safety. This study delves into the development of computational models to understand the rate of air permeation through these butyl rubbers in a comparative manner using molecular dynamics simulations. Through advanced molecular modeling techniques and comprehensive all-atom molecular dynamics simulations, we meticulously analyze molecular structures of BIIR, CIIR and IIR rubbers and gas transportation through these polymers. Our computational investigations highlight that CIIR has distinct structural features, particularly the presence and positioning of chlorine atoms, which significantly enhance its ability for slowing down the rate of transport of gas molecules (O ₂ , N ₂ and air). The overall trend of gas transmission rate among these polymers is IIR > BIIR > CIIR which is successfully validated with experimental result. These simulations provide deep insights into the molecular mechanisms that govern CIIR’s superior barrier properties, revealing how variations in initial conditions, available free volume, and the interaction of functional groups with gas molecules contribute to its enhanced air retention properties. By elucidating these transportation phenomena, this research not only advances our fundamental understanding of rubber material science but also underscores the pivotal role of selecting suitable polymer wherever barrier property of tyre and tube are required through computational approach. These findings serve as a tool for understanding the required future advancements in developing safer and high fuel-efficient tyres.