The Structure Of Polymer Blends At Quiescence And Under Shear Flow With Or Without The Influence Of External Surfaces

The main aim in the research and application field of polymer blend is to tailor the structure of multiphase materials by various means, such as component ratio and processing parameter. Besides the thermodynamics of system, the presence of an external flow field or an external surface will also contribute to the various kinetically behavior of polymer blends. Thus, to obtain better understanding about the phase behavior of multiphase under complex coupling conditions, and to find better optimum organization of structure is of significant importance both in theoretical research and industrial application.This dissertation focused on the structure formation of both immiscible and miscible blend in the presence of shear flow or external surface (including fillers and substrate). Optical-Shear technique was utilized to study the structure evolution of two model immiscible polymer under shear and quiescence conditions. And then, the deformation and relaxation dynamics of filled dispersed phase in polymer blend were investigated for the first time. The thermodynamics stability of two partial miscible polymer blends with distinct viscoelastic characteristics was probed. Theoretical prediction accounting for the impact of inorganic fillers on the miscibility was compared and discussed with experimental result. Finally, mesoscopic simulation was performed to examine the pattern formation of binary blend in the presence of filler, substrate and complex temperature history. The main contents and conclusions are listed as follows: 1. The structure of immiscible polymer blends under shear flow. (a) Three methods for the measurement of interfacial tension were discussed and compared. Interfacial tension analysis software was developed and was utilized to obtain the interfacial tension of polyamide 6 (PA6)/polystyrene (PS) and PS/high density polyethylene (HDPE). (b) A new method to measure the orientation angle of a deformation droplet on optical-shear setup was proposed. (c) Unique core-shell droplet was found in PS/HDPE dispersed blend. Systematical shear experiments were conducted to reveal the formation, relaxation and breakup behavior of core-shell droplets. The results were concluded as a dynamical morphology map. (d) The formation, breakup of HDPE melt film in PS matrix prior to the formation of co-continuous structure during the early stage of melt mixing was investigated in-situ. The development of hole on the film and the formation and disintegration of a melt network was visualized and discussed. A semiquantitative expression was derived to capture the physical nature of hole growth in a melt film immersed in another immiscible matrix.2. Morphology evolution of immiscible blends in the presence of fillers. (a) The incorporation of glass beads in the dispersed phase of PA6 made it difficult to deform under shear flow. Also, filled system shows slower relaxation dynamics. Upon the incorporation of SiO₂ particles, the critical break aspect ratio of PA6 at 230°C increased from 8.5 to 11. The results were discussed based on the increase in viscosity of PA6. (b)The SiO₂ particles accelerated the coalescence rate of dispersed phase in PA6/PS blend. The strong interaction between PA6 and SiO₂ particle was believed to be responsible for this change. (c) It was found that SiO₂-filled HDPE droplet was more difficult to form a melt film in PS matrix. The growth rate of hole in HDPE film was reduced greatly.3. Phase behavior of miscible blends with fillers. (a) The phase diagrams of a kinetically symmetric blend poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) and a kinetically asymmetric polystyrene/poly(vinyl methyl ether) (PS/PVME), were constructed with the aid of microscopy and rheology technique. The thermodynamics stability of PMMA/SAN was improved by selective fillers. The result was compared with the prediction of particle-compatibilizing theories based on modified Flory-Huggins equation, proposed by Lipatov et al. and Ginzburg. (b) The viscoelastic phase separation of PS/PVME blend showed distinct dependence on the component ratio and temperature. (c) SiO₂ particles with a diameter about 2.5μm did not change the phase diagram of PS/PVME. The wetting of PVME on SiO₂ particle initiated rapid hole growth near particle surface and destabilized the phase separating blend film.4. Simulation on the phase behavior of binary blend under the influence of complex thermal history and external surface. (a) By using cell dynamics system method, lamellar structure was found both in critical and off-critical blends which were subjected to a two-step quench. The formation of lamellar phase was ascribed to the existence of interface between two phases. (b) Parallel and target-like composition waves were initiated in the vicinity of a selective substrate and immobile fillers. The extent of composition wave was found to depend on the composition, temperature and initial composition fluctuation of system. (c) Under two-step quench conditions, the composition waves were more pronounced. Increasing the filler concentration suppressed the formation of lamellar structure in the bulk area and limited the range of composition wave near the filler surface. (d) Compositional waves were also formed in the vicinity of particle cluster produced by diffusion-limited aggregation (DLA) of fillers...