Surface modification of PDMS via self-organization of vinyl-terminated small molecules

Polydimethylsiloxane (PDMS) elastomers are widely used in soft lithography, microfluidics and biomedical applications as they combine a range of desirable chemical and physical properties. We studied the surface of PDMS modified using surface enrichment with long-chain alkenes. These alkenes were immobilized during crosslinking of the PDMS pre-polymer mixture cast against a template of matching surface energy. A range of different functional groups was introduced, including perfluorinated and oligoethylene glycol groups, alkyl chains and initiators for controlled radical polymerization. A detailed analysis of the composition of the modified PDMS surfaces was carried out using contact angle measurements, AFM, SIMS and XPS. The results demonstrate that the PDMS was enriched with small molecules near the surface and show that the functional molecules follow the template surface energy on patterned surfaces with edge resolutions equal to the template. By introducing hydrophilic alkenes receding contact angles on PDMS can be lowered below 5°, and we investigated how these surfaces rearrange in air due to the chain mobility of the PDMS backbone and PDMS short-chain fragments.