Influence of precursor molecular weight on swelling and elastic modulus of cross-linked PDMS films

Si NMR confirmed the consumption of trimethoxysilane end-groups and the formation of Si-O-Si junctions, while also revealing restricted mobility near cross-linking sites. Nanoindentation provided independent measurements of Young's modulus, which were compared with predictions from the Flory-Rehner model. The results demonstrate that increasing precursor molecular weight decreases cross-link density, enhances swelling, and reduces modulus, providing a consistent picture of the network architecture in thin PDMS films. Beyond polymer physics, this strategy offers a simple means to modulate elasticity without altering surface chemistry, with potential implications for applications such as biointerfaces, microfluidics, and soft lithography.