SURFACE ENRICHMENT AND SURFACE-TENSION OF OLIGO(STYRENE) OLIGO(DIMETHYLSILOXANE) BLENDS NEAR THE CRITICAL-TEMPERATURE/

Surface tensions of oligomer mixtures are theoretically and experiment ally investigated in terms of surface enrichment. Surface tension is m easured for blends of oligo(styrene) (OS) and oligo(dimetylsiloxane) ( ODMS) as a function of composition and temperature in a one-phase regi on including the vicinity of critical point. With increasing ODMS cont ent, the surface tension decreases dramatically, approaches the value of pure ODMS around 20 wt% ODMS, and then decreases very gradual, exhi biting a little sharp decrease to reach the value of pure component. T he temperature dependence of the surface tension of the critical mixtu re is slightly weaker than those of pure polymer liquids, but shows no anomalous change near the critical point. Composition profiles and su rface tension are calculated for the present system by a square-gradie nt theory, where the system is described as a phase-separated three-co mponent mixture consisting polymer 1, polymer 2, and holes. The experi mental results are well described by the theory. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.