Surface chemical composition and surface molecular mobility of diblock and random copolymers with hydrophobic and hydrophilic segments

The A-B type diblock copolymer composed of polystyrene (PSt) and poly(methoxy poly(ethylene glycol) methacrylate) (PMPEGM) and their corresponding random copolymer were prepared. MPEGMs with different poly(ethylene glycol) (PEG) chain lengths were used to change the hydrophilicity and molecular mobility of hydrophilic segments. The surface chemical composition and surface molecular motion of these copolymers were investigated by X-ray photoelectron spectroscopy and dynamic contact angle measurement. The dependence of surface composition on casting solvents was prominent for the block copolymer system, whereas the random copolymer did not show this effect. Dynamic contact angle measurements revealed that the advancing contact angle decreased with successive immersion in water. Also, the motional scale of PMPEGM on the block copolymer surface increased with PEG side chain length. In contrast, the magnitude of advancing and receding contact angles for the random copolymer surface did not change with repeated immersion.