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Tuning the Effective Viscosity of Polymer Films by Chemical Modifications

Yu, Xuanji, Wang, Tong, Tsui, Ophelia K. C., Weng, Lu-Tao
Macromolecules 2019 v.52 no.9 pp. 3499-3505
X-ray photoelectron spectroscopy, chemical analysis, films (materials), hydrodynamics, hydrofluoric acid, moieties, ozone, polystyrenes, silicon, viscosity
We report controllable adjustment of the flow dynamics of polystyrene films supported by oxide-covered silicon by using a combination of ultraviolet ozone (UVO) treatment of the polymer and variable treatments of the substrate that adjust the contents of Si–OH and Si–H groups on the surface. The latter were achieved by submerging the substrates in a piranha solution and then in deionized water (leading to enrichment of Si–OH) or an aqueous hydrogen fluoride solution (leading to enrichment of Si–H) or both (leading to intermediate surface chemistry). X-ray photoelectron spectroscopic chemical analyses showed that the UVO treatment produced oxygenated functional groups in the polymer. Alongside, effective viscosity (ηₑff) of the films became enhanced. However, the degree of enhancement increases (decreases) with the content of Si–OH (Si–H) groups on the substrate surface, ascribable to the resulting increases in the attractive interactions between the UVO-induced oxygenated groups in the polymer and Si–OH on the substrate surface. Likewise, ηₑff of the pristine films displayed increases with the Si–H content on the substrate surface, corresponding to increases in the polymer–substrate interaction. Our observations pave the way for strategic tuning of the dynamics of polymer films by modulating the polymer–substrate interactions by chemical modifications.