Effect of a metal substrate on the degradation mechanisms of multiply-alkylated cyclopentane space lubricants

The operational lifetime of mechanical systems in space applications depends upon the stability and durability of their lubricants. Among the lubricants suitable for extreme space conditions, multiply-alkylated cyclopentane (MAC) oils are widely employed. However, the factors that affect MAC lubricant lifetime are not fully understood. One factor is speculated to be lubricant degradation catalyzed by the nascent metal surfaces that are exposed by wear of native oxide layers. This work utilizes reactive molecular dynamics (MD) simulations to investigate thermal degradation of the MAC lubricant 1,3,4-tri-(2-octyldodecyl) cyclopentane. The simulations compare a MAC oil between nascent iron or iron-oxide slabs, representing the surfaces of mechanical assemblies, or without metal surfaces present as a reference. The chemical species formed by degradation of the MAC at elevated temperatures are tracked in the simulations and the most abundant species are consistent with previously reported experimental findings. The reactive MD simulations also reveal reaction pathways for degradation, contributing to a deeper understanding of the mechanisms of degradation for MAC oils that lubricate mechanical systems in space applications.