Effects of low-molecular-weight additives on interfacial tension of polymer blends: experiments for poly(dimethylsiloxane)/poly(tetramethyldisiloxanylethylene) plus oligo(dimethylsiloxane), and comparison with mean-field calculations

The effects of low-molecular-weight additives on the interfacial behavior o f polymer blends have been studied experimentally and theoretically. The me asured interfacial tension near the critical solution temperature T-c for p oly(dimethylsiloxane)/poly(tetramethyldanylethylene) as a function of tempe rature is merely shifted by the addition of oligo(dimethylsiloxane) corresp onding to the decrease of T-c, giving only a subtle adsorption effect in in terfacial behavior. Theoretical calculations have also been carried out for polymer/polymer/additive ternary systems using the square-gradient theory (SGT) and the dynamic mean-field (DMF) calculation. The experimental result s are quite consistent with theoretical predictions. Further theoretical ca lculations demonstrate that higher molecular weights and less miscibility w ith matrix polymers are most effective for a large adsorption of additives in the interface, leading to a large reduction of interfacial tension. SGT and DMF are found to predict almost the same interfacial tension and compos ition profiles in ternary polymeric systems. (C) 2001 Elsevier Science Ltd. All rights reserved.