EFFECT OF WATER IMMERSION ON SURFACE CONFIGURATION OF AN ETHYLENE-VINYL ALCOHOL COPOLYMER

Ethylene-vinyl alcohol copolymer (44 mol % ethylene) contains very hyd rophilic -OH groups randomly distributed in very hydrophobic hydrocarb on co-monomer units. The hydrophilicity of surface of a film, therefor e, is determined by how many -OH groups are actually located on the su rface (surface configuration). Contact angle of water and O/C analysis by ESCA were used to investigate how surface configuration of film ch anges as a consequence of immersion of a film in water. The take-off a ngle dependence of ESCA analysis indicates that many -OH groups are bu ried in the inner region of the top surface in a dry state. Samples im mersed in water (and freeze-dried) show that -OH groups are brought to the top region of the surface and increase the O/C ratio at the top r egion. The contact angle of water also decreases with water immersion. Because of this surface-configuration change caused by contacting wit h liquid water, a pronounced hysteresis effect (between advancing and receding contact angles) is also observed.