Hydrophilic (hydrogen-bonding) polystyrene surface by substrate-induced surface segregation of benzene groups

The measurement of contact angle on polystyrene (PS) films solvent cast on acid-cleaned glass substrates was used in conjunction with the Lifshitz-van der Waals/acid-base approach in order to investigate the surface functiona l-group compositions as well as the physical nature and the strength of int ermolecular interactions between the film surfaces and various testing liqu ids. The static contact angle for water observed on the air-side surface of the films (80 degrees) was consistent with the literature. However, the gl ass-side surface of the films was found to be hydrophilic with a water cont act angle of 62 degrees. This hydrophilic character was shown to arise from (i) the substrate-induced surface segregation of benzene groups in the fil m casting process with consequent formation of benzene-rich PS surface and (ii) the relatively strong hydrogen-bond-accepting (electron-donating) char acter of the aromatic rings of polymer. The strength of hydrogen bond betwe en the water molecule and the aromatic moiety was estimated to be greater t han or equal to 10.6 kJ/mol.