Preparation and characterization of alkylated poly(vinyl alcohol) hydrogels using alkyl halides

A poly(vinyl alcohol) hydrogel coated onto polyethylene was partially alkylated by reaction with an alkylhalide (C4, C8, or C18) in the presence of a deprotonating agent (sodium ethoxide or potassium tert-butoxiDATE Surface coverage determined by X-ray photoelectron spectroscopy (XPS) was respectively approximately 34, 25, and approximately 8% for the C4, C8, and C18 modified surfaces. Statistically significant differences were observed in the fraction of C8 and C18 grafted alkyl groups as a function of depth (i.e. take-off angle) indicating the presence of a verticle composition gradient. All three surfaces showed maximal surface coverage of alkyl groups after 1 h reaction. At this reaction time, no further coverage was observed beyond a base/PVA ratio twenty times greater than the stoichiometric ratio. The advancing contact angle data exhibited an increase in hydrophobicity that correlated with the degree of coverage obtained by XPS: 90 +/- 1, 83 +/- 0.5, and 71 +/- 1 deg for C4, C8 and C18 alkylated PVA, and 55 +/- 2 deg for PVA respectively. Large contact angle hysteresis was observed on all three surfaces consistent with surface heterogeneity.