The adhesion and stability of hydrophilic polymer thin films on hydrophobic substrates prepared from aqueous solutions are of paramount interest in many applications. There are very few literature reports on this subject due to the challenging nature of the destabilizing polar interactions during solvent evaporation. In this research, the hydrophobic substrates were prepared by covalently attaching polydimethylsiloxane (PDMS), tridecafluoro-1,1,2,2-tetrahydrooctyl dimethylchlorosilane (F13), and trimethylchlorosilane (TMS) to silicon wafers. Poly(vinyl alcohol) (PVOH88%H, 87-89% hydrolyzed; PVOH99%H, 99+% hydrolyzed) thin films were fabricated using two methods - spontaneous adsorption and spin coating. The PVOH thin films were characterized by ellipsometry for thickness, contact angle goniometry for wettability, optical microscopy for microscopic morphology, and atomic force microscopy for nanoscopic morphology. Their stability upon water immersion and thermal annealing was probed as a function of fabrication method, PVOH degree of hydrolysis, and type of substrate. In general, the spin coated films are less stable, likely due to the faster drying rate. Compared to the PVOH88%H films, the PVOH99%H films are more stable because of the higher degree of crystallinity. Among the various parameters, it was found that the type of substrate has the largest effect on the PVOH film stability. For example, extensive dewetting on the microscopic-scale was observed on the PDMS substrate while wetting or nanoscopic dewetting takes place on the F13 substrate. The significant difference is attributed to the mobility of the underlying PDMS substrate destabilizing the PVOH films.

Investigation of adsorption and spin coating of poly(vinyl alcohol) on hydrophobic substrates

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