Surface composition control via chain end segregation in blend films of polystyrene and poly(vinyl methyl ether)

Surface aggregation states in miscible blends of monodisperse polystyrene (PS) and poly-(vinyl methyl ether) (PVME) were studied by X-ray photoelectron spectroscopy (XPS) in conjunction with neutron reflectivity (NR). In the case of symmetric blends in terms of degree of polymerization, N, PVME and PS were preferentially segregated at the film surface and the interface with a silicon wafer, respectively, to minimize free energy of the system. The concentration profile near the surface obtained by experiments was consistent with a mean-field prediction. Also, the surface composition in symmetric blends composed of PS terminated by fluoroalkyl groups at both ends (α,ω-PS(R_f)2) and PVME was examined. In this case, the surface enrichment of PVME was suppressed by virtue of the surface localization of fluoroalkyl end groups, and the composition was strongly dependent on N. The surface in asymmetric α,ω-PS(R_f)₂/PVME blend, in which N of α,ω-PS(R_f)₂ was much smaller than that of PVME, was mostly covered with the PS segments. The results presented imply a possibility that the surface composition in miscible polymer mixtures could be perfectly regulated combining the chain end effect with the molecular weight disparity between the components.