Enhancing hydrophobicity of electrospun poly(vinyl alcohol) fibers by chemical reaction of hydroxyl groups

Abstract

Poly(vinyl alcohol) (PVA) fiber mats having fiber diameters in a sub-micron range were first prepared by electrospinning. Most chemical modification reactions were conducted on PVA fiber mats electrospun from 10%(w/v) PVA solution, having a diameter of 297.05 ± 33.59 nm and an air-water contact angle of 52.31° ± 1.22°. Esterification of hydroxyl groups of PVA by acyl chlorides was not an effective route to hydrophobize the PVA fiber mats. The reactions led to the deformation of the fibers. Silica-like inorganic layer of SiO₂/SiOH was then introduced to the PVA fiber mats via 3 cycles of a reaction with SiCl₄ and H₂O in order to increase the strength and integrity of the PVA fiber mats. Hydrophobization of the PVA-silanol fiber mats were thus performed using silanization of alkylchlorosilanes both in vapor and solution phases. Surface modified PVA fiber mats were characterized by water contact angle (WCA) analysis and scanning electron microscopy (SEM). The PVA fiber mats became extremely hydrophilic with WCA ~ 0° after the SiO₂/SiOH layer was generated. Although the advancing WCA reached as high as 150° after silanization with alkylchlorosilanes, the receding WCA remained at 0°, leading to an extremely high contact angle hysteresis. The water drop remained intact with the silanized fiber mats and did not roll off although the fiber mats were flipped up-side down. These characteristics suggest that all silanized PVA fiber mats cannot be considered superhydrophobic.