Study On The Phase Behavior Of Binary Polymer Blend Under Shear

In the past, most of the studies relative to polymer miscibility had been focused on those within the frame of classical quiescent thermodynamics. As well known, however, polymers will undoubtedly experience strain and stress under processing conditions, during which not only the thermodynamical but also the dynamical and mechanical factors will strongly influence the phase structure of polymer blend and those conclusions made under quiescent equilibrium state will fail due to their ignorance of the non-equilibrium effects. Being driven by the requirements of theoretical study as well as the demands from industry, the study on the phase behavior of polymer blend under shear has been developed into a very important aspect of the research field of the multi-component polymer system.Within this dissertation, both thermodynamical and hydrodynamic effects of shear are considered, for the first time, in the modeling of the shear-induced phase behavior of binary polymer blend. For experimental purpose, a customized device named Rheo-SALS Tester was developed with reference to our previous one as well as those reported in documents. The most inspiring merit of this device is its capability of simultaneous measuring micro morphology along with macro stress response of sample, which makes possible the run-time study of the direct relation between structure and the corresponding properties. Then, with the aid of the Rheo-SALS Tester and optical microscope, the thermodynamical and kinetic phase behavior as well as the rheological activities of binary polymer blend (polystyrene / polyvinylmethylether) under simple and oscillatory shear were intensively studied. The main work and key conclusions come as follows:1. A customized Rheo-SALS Tester was developed for experimental purpose, which is able to simultaneously measure the collective structure of macromolecules and the corresponding rheological behavior. If compared with those previously reported similar ones, this device has some distinct merits: (1) it is able to concurrently measure the micro morphology (by SALS) and macro rheology (rheological tester), which makes possible the establishment of the real-time relationship between structure and properties; (2) Withthe Distributed Control System (DCS), this device centralizes the management, operation, and display but distributes the function, load, and danger; (3) the programmable shear unit can be secondarily programmed to realize more shearing style, which provides rich choices to the study of macromolecules' collective structure under shear; (4) the device has a good expandability, which provides an excellent adaptability as well as an easy and economical upgradeability; et al.2. With references to other research group's pioneer works, a model of the phase behavior of binary polymer blend under shear was established, within which the thermodynamical and hydrodynamic effects of shear are coupled for the polymer blend, for the first time, hi the modeling, the idea of extended irreversible thermodynamics (BIT), "two-fluid" model, and "double reptation" were adopted. It's found that, this theory can predict both "miscibiliry gap" and anisotropical phase separation of polymer blend, while the two different previous theories, that is the pure thermodynamical one and hydrodynamic one, could only predicts one but not both of them.3. With the aid of Rheo-SALS Tester, the phase behavior of PS/PVME under quiescent and shear state was briefly studied. Both the scattering and rheological results indicated that the phenomenon similar to "double cloud point", which has been found along the vorticity direction by previous studies, could be also observed in the velocity direction, which confirms the prediction of the above theory that the polymer blend will exhibit anisotropical complex phase diagram (for example, miscibility gap) under shear. It's also found that the mixing along vorticity direction was reduced by weak shear but enhanced by strong shear. In addition, the more remarkable the molecular weight difference...