Air leakage in seals with application to syringes

TL;DR

This paper investigates air leakage in syringe seals, analyzing how surface roughness and material properties influence leak rates, and compares experimental data with a theoretical model emphasizing ballistic flow in narrow channels.

Contribution

It introduces a combined experimental and theoretical approach to model air leakage in syringe seals considering multiscale contact mechanics and ballistic gas flow.

Findings

Leak rates depend on surface roughness and material properties.

Ballistic (Knudsen) flow dominates in narrow leakage channels.

Theoretical predictions align with experimental measurements.

Abstract

We study the leakage of air in syringes with Teflon coated rubber stopper and glass barrel. The leakrate depends on the interfacial surface roughness, the viscoelastic properties of the rubber and on the elastoplastic properties of the Teflon coating. The measured leakage rates are compared to the predictions of a simple theory for gas flow, which takes into account both the diffusive and ballistic air flow, and the elastoplastic multiscale contact mechanics which determines the probability distribution of interfacial separations. The theory shows that the interfacial air flow (leakage) channels are so narrow that the gas flow is mainly ballistic (the so called Knudsen limit). The implications for container closure integrity is discussed.