화학공학소재연구정보센터
Macromolecules, Vol.32, No.12, 4098-4105, 1999
Surface enrichment in a miscible random copolymer blend: Influence of polydispersity and architecture
Neutron reflectivity and low-energy forward-recoil spectrometry were used simultaneously to monitor surface segregation in blends of poly(styrene-ran-acrylonitrile), dSAN23 and SAN27, having 23 and 27 wt % AN, respectively. Because of its lower AN content, dSAN23 was found to partition at the polymer/air interface, in agreement with the work of Mansfield et al. (Physica B 1991, 173, 207) and Kim et al. (Polymer 1995, 36, 2427. In contrast to the previous studies, this work explores surface segregation at high dSAN23 bulk volume fractions, phi--- (i.e., phi--- > 0.50). New results include the observation of a maximum dSAN23 surface excess (similar to 75 Angstrom) near phi--- approximate to 0.35 and a dSAN23 surface volume fraction that approaches 1, rather than 0.75, as phi---, increases to 1. The dSAN23 profile deviates from the exponential profile predicted by Schmidt-Binder and self-consistent mean-field (SCMF) models. For phi---, > 0.50, the profile displays a surface flattening not observed at low phi---,. The SCMF model is extended to account for polymer polydispersity. Although thicker than the monodisperse profile, the polydisperse profile does not capture the experimentally detected surface flattening. Coil deformation along the surface is given as a possible explanation.