# Molecular Dynamics Simulation of Silicone Oil: Degradation upon Oscillatory Testing

## TL;DR

This paper uses molecular simulations to study how silicone oils degrade under repeated mechanical stress, revealing that cyclic silicone molecules are more persistent and reactive.

## Contribution

The study introduces a novel simulation approach to assess silicone oil degradation mechanisms under oscillatory stress, revealing the role of cyclic silicone ring formation.

## Key findings

- Cyclic silicone moieties show greater persistence during compression/decompression cycles.
- Degradation leads to the formation of cyclic silicone molecules with varying ring sizes.
- Si-O bonds in cyclic silicones undergo cleavage and reformation, enabling ring fusion and fragmentation.

## Abstract

The fate of a selection of linear and cyclic silicone oil formulations in heavy-duty fluid dampers is studied from molecular dynamics simulations. Mimicking cyclic agitation to all-atom simulation models, we elaborate oscillatory compression/decompression runs that feature degradation reactions within only hundreds of loading cycles. This enables the assessment of chain scission, reassembly and cyclization mechanisms from ns-scale molecular dynamics simulations. Using analogous testing scenarios, we compare the degradation reactions of linear and cyclic silicone chains and demonstrate the importance of silicone ring formation. In turn, cyclic silicone moieties show relative persistence in our compression/decompression runs. We conclude that long-term degradation finally leads to a manifold of cyclic silicone molecules, featuring rings of up to tens of monomeric units. The underlying molecules are not inert to Si-O bond cleavage and reformation, but feature reactivity in terms of the fusion of small to large rings and vice versa.