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

The effects of low-molecular-weight additives on the interfacial behavior of polymer blends have been studied experimentally and theoretically. The measured interfacial tension near the critical solution temperature T_c for poly(dimethylsiloxane)/poly(tetramethyldisiloxanylethylene) as a function of temperature is merely shifted by the addition of oligo(dimethylsiloxane) corresponding to the decrease of T_c, giving only a subtle adsorption effect in interfacial 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 results are quite consistent with theoretical predictions. Further theoretical calculations demonstrate that higher molecular weights and less miscibility with 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 composition profiles in ternary polymeric systems.