Formatting Issue - Best Available Paper/Graphic The glass transition temperature of thin poly(alpha-methyl styrene) films measured by flash differential scanning calorimetry

摘要

The glass transition temperature in thin polymer films has been widely studied using different experimental methods. It has been frequently reported that T_g deviates from that of the bulk as the film becomes thinner. A very large reduction in T_gis observed for free standing thin films of polystyrene whereas a decrease or increase in T_g has been reported for supported polymer thin films5. A leading hypothesis is that the free surface mobility is responsible for the T_g reduction. However, interestingly Paeng and Ediger7 find that there is no mobile surface layer for poly(a-methyl styrene). Because there is much speculation that surface liquid layers lead to the observed reduced T_g in ultrathin films, the poly(a-methyl styrene) becomes an important material to study. Here we report on the glass transition temperature in ultrathin films of poly(a-methyl styrene) using flash differential scanning calorimetry as a function of film thickness and substrate surface energy. T_g behavior of untrathin poly(a-methyl styrene) films is examined by placing the sample either on a bw energy grease (Apiezon ® ～ 19mN/m)~8 or directly on Si_3N_4 chip having a higher surface energy (38 rnN/m)~9 in order to examine the calorimetric response of films under differing surface adhesion conditions.