Metal-polymer interfaces and their effect on the glass transition of thin polystyrene films

摘要

We present a study of polystyrene-metal interfaces and discuss the relationship between the interfacial structure and anomalies in the measured glass transition temperature (T{sub}g) of thin metal capped polystyrene (PS) films. The PS films used in these studies were coated with an evaporated metal layer of either Aluminum (Al) or gold (Au) and the T{sub}g values were measured with ellipsometry. Uncoated PS films were also measured and these samples showed T{sub}g values that were reduced relative to the bulk value for film thicknesses (h) less than 40 nm. Films coated with Au were shown to have measured T{sub}g values that were the same as the bulk value (T{sub}g{sup}(bulk)=370 K) for all the film thicknesses studied (h≥8nm). The Al coated PS films had measured T{sub}g values that were the same as the uncoated PS films. The observed differences are discussed in terms of the differences in the structure of the metal-polymer interfaces produced during thermal evaporation of the metal layers. A novel sample preparation procedure was developed to enable us to use Atomic Force Microscopy (AFM) to directly measure the structure of the buried polymer-metal interfaces. The measurements performed on these systems support the suggestion that the interfacial structure is different for the two metal-polymer interfaces studied and that these differences may be the cause of the anomalies in the measured T{sub}gs of these samples.