Thin film coatings can modify a surface to impart desired surface properties while preserving bulk properties of the underlying material. Polyvinylpyrrolidone (PVP) is a nontoxic, hydrophilic polymer and has a wide range of applications. In this research, PVP thin films were prepared from aqueous solution on silicon wafers via static adsorption and spin coating methods. Among many water-soluble polymers examined, PVP is the only polymer that spontaneously adsorbs to silicon wafers, resulting in a layer that is ~ 1 nm in thickness. The lack of pH-dependence of the adsorbed amount disputes the previously reported hydrogen bonding being the driving force for adsorption. Spin coating of PVP solutions on silicon wafers was carried out to prepare PVP films with larger thickness values. The PVP thin films were characterized by ellipsometry, contact angle goniometry, and atomic force microscopy. All the PVP films prepared are pin-hole free, continuous on silicon wafers. The wettability of the films was found to be greatly affected by the preparation method instead of film thickness. The stability of the PVP films was probed by water immersion and thermal annealing. Upon water immersion, the spontaneously adsorbed films do not decrease in thickness while the spin-coated films lose the spin-deposited portion. Nonetheless, dewetting is not observed with all the PVP films indicating that the PVP thin films are stable on silicon wafers.

Continuity and stability of polyvinylpyrrolidone thin films on silicon wafers

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