Quantitative rationalization of unexpectedly moderate water wettability on poly (vinyl alcohol) surfaces: Thermodynamic Evaluation and Prediction of Surface Hydrogen Bonding

Abstract

In this work, a series of poly (vinyl alcohol) (PVA) films with defined but varied water wettability were prepared by curing as-prepared PVA films at systematically adjusted temperatures. The polar components of surface energy (γ^(s,p)) of the resulting PVA films were calculated and correlated with the molecular configurations of their surface OH groups – free OH (〖OH〗_f), trans-hydrogen bonded OH (〖OH〗_t), and gauche-hydrogen bonded OH groups (〖OH〗_g) – with the aid of attenuated total reflectance Fourier transform infrared spectroscopy. By decomposing the γ^(s,p) values of the PVA films as a sum of the contributions of 〖OH〗_f, 〖OH〗_t, and 〖OH〗_g groups, the intrinsic γ^(s,p) components of 〖OH〗_t (γ_t^(s,p*)) and that of 〖OH〗_g (γ_g^(s,p*)) were calculated to be 8.0 mN/m and 9.8 mN/m, respectively, which were substantially smaller than that of 〖OH〗_f (γ_f^(s,p*)of 50 mN/m). This laid a thermodynamic foundation not only to rationalize the unexpectedly moderated surface hydrophilicity of PVA films but also to quantitatively predict the f_HB component of hydrogen-bonded OH groups on their surfaces according to their water wettability.