Quantitative rationalization of the unexpectedly moderate water wettability of 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 was 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 from OH_f, OH_t, and OH_g groups, the intrinsic γ^s,p components of and were calculated to be 8.0 mN m⁻¹ and 9.8 mN m⁻¹, respectively, which were substantially smaller than that of . This provided 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.