The Kinetics Of Multi-component's Polymers Phase Separation

The phase separation of triblock copolymers is one of most complicated problems in the study of multi-component polymer system. The morphologies formed by triblock copolymers are more complex and richer than those formed by diblock copolymers. And these microstructures not only can be used as templates for nano-fabrications but also are nano devices. However, most previous studies have concerned on the equilibrium morphologies formed by triblock copolymers. As we known, there are few works concerning on the kinetics of phase separation. The study of kinetics of triblock copolymers can provide proper ways to control their phase separation and achieve the expected microstructures. The phase separation of polymer dispersed liquid crystals is another important subject in multi-component polymers system, because they are not only a new class of materials for optical device applications but also a classical branch of soft matter physics. And the phase separation of PDLC is a process of unmixing between polymer and liquid crystals and ordering of the liquid crystals. However, as we known, there is no effort concerning on surface effect on the PDLC. The kinetics of the triblock copolymer and surface effect on PDLC were explored by experiment and theory in our thesis.1. We have extended the dynamic density functional theory to study kinetics of linear and star triblock copolymers by a continuous self consistent method. When triblock copolymers are quenched from a disordered state, in general, the ordering dynamics involves a fast initial phase segregation followed by an extremely slow defect annihilation process, which agrees well with the experimental observation of Cochran et al. The time evolution of the phase structures and corresponding order parameters were obtained in the DDFT simulation. A careful examination of the morphologies and order parameters reveals that the mechanisms of the complex ordering in ABC triblock copolymers can be divided into two types: the one-step mechanism M_I, in which all the three species segregate simultaneously after the system isquenched from a disordered state, and the two-step mechanism M_II, in which segregation of one species from the other two occurs first, followed by separation of the two mixed species. The present DDFT study shows that a two-step microphase separation can be achieved by simply quenching a triblock copolymer from the disordered state into an ordered state (only one temperature jump is needed), instead of changing the interaction energies among different species through continuously varying temperature (many adjustments to temperature) or adding a selective solvent.2. Two linear triblock copolymers, poly(styrene-b-isoprene-b-methacrylate) (SIM), were synthesized by standard sequence anionic polymerization. Their morphologies in bulk are lamellar phase and cylinder phase respectively, which were confirmed by TEM. Then phase behavior of triblock copolymer in dodecane and dimethyl phthalate solution was measured by small angle X-ray scattering. Dodecane is selective solvent for polyisoprene, otherwise dimethyl phthalate is selective solvent for polystyrene and polymethacrylate. For example, when the DMP was added into SIM and the polymer concentration is greater than 50w%, lamellar structure was observed both for two triblock copolymers; when the concentration is lower than 50w%, micelles and Janus cylindrical phase were obtained for SIM with lamellar phase and cylindrical phase in bulk, respectively. The phase behavior of triblock copolymers in dodecane is relatively simple. The addition of dodecane into SIM is qualitatively equivalent to raising the volume fraction of polyisoprene, which induced a lytropic order-order transition as the concentration of polymer decreasing. Another characterization in our experiment is that the microstructures formed by triblock copolymers in selective solvent depend on selectivity of the solvent.3. The phase separation kinetics of polymer dispersed liquid crystals (PDLC) confined between two parallel hard walls are numerically studied. The spatial-temporal evolution of both conserved compositional order parameter and nonconserved orientational order parameter during the spinodal decomposition are calculated. The tensorial nature of orientational order parameter is considered. A surface-induced ordering transition of LC at the walls is observed, and it is faster than that in the away-from-surface regions due to the fact that the walls adsorb LCs. Periodic structures are achieved when the surface effect dominates over the phase separation kinetics. The phase separation kinetics of PDLC as well as the nematic ordering transition are accelerated as the external confinement is intensified. The present results may provide insights into producing patterned ultrathin PDLC films with enhanced optical performance (e.g., faster switching speed) and devices based upon them. The simulations are performed in two dimensions. We envision that the three-dimensional calculations may carry more interesting features because ofthe presence of long-range orientational correlations in neighboring LC domains.4. It has been reported that surface effects have great influences on the phase separation of polymer blends and block copolymers. However, there is still no effort to study the surface effects (i.e. pattern surface with different chemical property) on phase separation of polymer dispersed liquid crystals. In this paper, gold rings patterned ITO surface was prepared by evaporation induced self assembly method. The advantage of this method is that the width of the gold rings is gradient. Then the toluene solution of polystyrene and 5CB mixtures covered on patterned surface. During the evaporation of toluene, the phase separation of mixtures induced by gold rings patterned ITO glass was observed. The liquid crystals, 5CB, was accumulated on two edges of the gold ring like two rows of pearls at the beginning of the phase separation resulting from the gold have preferential absorption to the 5CB. In the late stage of phase separation, two rows of pearl-like liquid crystals merge into one big droplet and dispersed on gold rings regularly and separately. Thus we showed that the domains of a phase separating mixture of polymer and liquid can be guided into arbitrary structures by a surface with a prepatterned variation of surface energies.