Effect Of Dynamic Asymmetry On The Phase Behavior In Polymer Blends

Phase behaviour strongly affect the structure and performance of materials as an important physical phenomenon in polymer blends, as a result, it has been extensively studied from scientific and industrial viewpoints. Dynamic asymmetry refers to the difference of glass transition temperatures or viscoelasticity between components of polymer blends. Molecular mobility intensively influences the phase behaviour since concentration inter-diffusion is involved in the transition process from homogeneous state to heterogeneous state. The phase structure is directly related to the viscoelasticity of polymer blends, rheological method has been widely applied in the research work of phase behaviour due to its high accuracy and convenience. In this paper, we mainly investigate the phase behaviour of PMMA/SMA12 and PMMA/SMA28 with different dynamic asymmetry. The results are as follows:1. Concentration fluctuation temperatures of PMMA/SMA12 and PMMA/SMA28 was determined through rheological frequency sweep tests and double-reptation-self-concentration model prediction. Spinodal temperature was obtained with the mean filed theory of Fredrickson and Larson after deducting the effect of components moduli contribution and loss moduli. We discussed the effect of dynamic asymmetry on the concentration fluctuation of polymer blends based on the discrepancy of concentration fluctuation region of polymer blends. For PMMA/SMA12 with weak dynamic asymmetry, concentration fluctuation region was symmetric with composition, while pmma domianted blends owned stronger concentration fluctuation in PMMA/SMA28 system, which could be attributed to larger difference in glass transition temperature and fast-mode interdifusion of polymers.2. Shift factor indicates the temperature dependency of polymeric viscoelasticity. We found that the difference between model prediction and experimental result for PMMA/SMA12 and PMMA/SMA28through observation of components dependency of shift factor, the difference was ascribed to the interaction and inner action of components, finally, we discussed the limitations of self concentration model.3. Components and phase separation mechanisms bring complicated results in dynamics of phase separation. Apparent modulus were made up of components contribution and that from interface.We introduced Cahn-Hilliard theory into our prediction of the evolution of components modulus contribution. The complicated result of dynamics was the result of competition of components contribution and interface contribution.