Wetting of functionalized polyethylene film having ionizable organic acids and bases at the polymer-water interface: relations between functional group polarity, extent of ionization, and contact angle with water

Abstract

Abstract : This paper examines the wetting by water of low density polyethylene film modified at the polymer water (air) interface by introduction of polar organic functional groups (carboxylic acids, amines, and others). Water/polymer contact angles were determined for each of these interfaces; for interfaces containing acidic or basic functional groups, the contact angle was determined as a function of the pH. The observed contact angle was related to the hydrophilicity of these functional groups: as the hydrophilicity (as measured by Hansch pi parameters) increased up to a certain point, the contact angle decreased. Beyond that point, increased hydrophilicity had little additional influence on the contact angle. The result is interpreted in terms of water adsorbed on the polar interfacial functional groups: extensive hydration of interfacial groups having large negative pi parameters moderates their effective hydrophilicity. Keywords: Polyethylene, Wettability, Ionization, Acids, Bases, Monolayers, Gold.