Effects of natural aging on hydrophilicity and mechanical properties of PDMS in various storage environments.

Polydimethylsiloxane (PDMS) is a synthetic elastomer widely used in biomedical and industrial applications. Despite its widespread use, the natural evolution of its mechanical and surface properties over time remains poorly understood. In this study, we fabricated PDMS samples with base-to-curing agent mixing ratios from 5:1 to 30:1 and aged them for up to 8 weeks under six non-harsh conditions at room temperature. Contact angle measurements revealed increasing hydrophobicity with aging, with maximum increases up to 16.5°. Mechanical testing showed up to 130% increases in Young's modulus and 60% changes in flexibility after 5 weeks. Storage in mineral oil best preserved surface hydrophilicity, while storage in water best maintained mechanical integrity. These results provide a framework for optimizing PDMS storage conditions in microfluidic and biomedical device applications.