Physical surface modification of hydrophobic polydimethylsiloxane (PDMS) via adsorption of poly(vinyl alcohol) (PVOH), an amphiphilic, water-soluble and semicrystalline polymer, was evaluated as a method to hydrophilize PDMS surfaces. Specifically, dilute PVOH aqueous solutions were spin-cast onto PDMS substrates, which were prepared by covalently attaching linear PDMS of 2 kDa, 9 kDa, 17 kDa, 49 kDa, and 116 kDa to silicon wafers. PVOH morphologies and surface wettability were studied as a function of PDMS molecular weight, PVOH degree of hydrolysis, and residence (adsorption) time of PVOH solution. It was determined that a residence time of 1 min or longer was necessary to allow PVOH to adsorb at the solution–substrate interface. PVOH degree of hydrolysis as well as PDMS molecular weight play significant roles in the final PVOH film morphologies. In general, as PDMS molecular weight/thickness increases, dewetting of PVOH films becomes increasingly pronounced. With 88%-hydrolyzed PVOH, thin films transition from continuous, to honeycombs, to droplets. Surface hydrophilicity is greatly enhanced when surface coverage of PVOH is high. With 99%-hydrolyzed PVOH, instead of droplets, fractal morphologies were observed on PDMS substrates of high molecular weights. The formation of the fractal morphologies is hypothesized to be driven by PVOH crystallization in the drying process. The results from PVOH spin-cast onto PDMS substrates were congruent with those found via adsorption of PVOH onto PDMS in a parallel study. The similarities indicate that PVOH adsorption at the solution-substrate interface is the driving force for the attachment of PVOH thin films onto PDMS surfaces. The centrifugal force in the spin-cast process, however, provides directional control on PVOH morphologies. This study establishes that the morphologies and wettability of the PVOH thin films prepared on the PDMS substrates via spin-cast are directly affected by the physical characteristics of PVOH and PDMS.

Factors affecting morphologies and hydrophilicity of poly(vinyl alcohol) thin films spin-cast on polydimethylsiloxane substrates

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.