Surface relaxation behavior of proton- and perfluoroalkyl-terminated poly(2-vinylpyridine) films

Proton- and perfluoroalkyl-terminated poly(2-vinylpyridine) (P2VP-H and P2VP-C₂C₈^F) were anionically synthesized. Surface molecular motions of P2VP-H and P2VP-C₂C₈^F films prepared on hydrophilic silicon wafers were examined by lateral force microscopy (LFM). Surface glass transition temperature, T_g^s, of P2VP-C₂C₈^F was lower than that of P2VP-H probably due to the difference of the surface concentration of chain ends. Also, both T_g^s values were lower than each corresponding bulk glass transition temperature, T_g^b. Surface molecular motion in an ultrathin film was less activated than that of the thick film, although T_g^s in the ultrathin film remained lower than T_g^b. In the case of ultrathin films, the surface/interface area to volume ratio becomes larger, and thus the thermal molecular motion at the surface is affected by that at the polymer/substrate interface. Since molecular mobility on the substrate might be restricted owing to the polar attractive interaction between polymer segments and the hydrophilic substrate, the activation of surface molecular motion apparently turns weak for such an ultrathin film.