Miho Motoyama

Phase separation and gelation of polymer-dispersed liquid crystals

Abstract Polymerization-induced phase separation in polymer-dispersed liquid crystal is studied by computer simulations in two dimensions. The domain morphology resulting from phase separation is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter, taking into account the viscoelastic effects and gelation due to polymerization. Comparing the morphology of phase separation by temperature quench, it is shown that the viscoelastic effects and gelation enable the polymer-rich phase to form a stable interconnected domain even when the polymer component is minority. The experimental evidence consistent with this characteristic feature is also given.

Morphology of Phase-Separating Binary Mixtures with Chemical Reaction

We study morphology of chemically reacting binary mixtures quenched into a thermodynamically unstable region. One of the characteristic features of the system which has not been studied so far is that one can change the average volume fraction during the phase separation process. Computer simulations are carried out in two dimensions to show a rich variety of stable domain morphologies.

Phase separation of liquid crystal–polymer mixtures

Abstract Phase separation in liquid crystal–polymer mixtures is studied by computer simulations in two dimensions. The domain morphology resulting from the phase separation either by temperature quench or by polymerization is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter. In a temperature quench, it is found that transient concentric domains are constituted near the nucleation regime of nematic ordering. Phase separation induced by polymerization is modeled by taking into account the time dependence of the molecular weight of polymer chains. Assuming a strong concentration dependence of the mobility, a transient network-like domain of polymer-rich phase is formed. The morphology is compared with the experimental results.

Microphase separation in rod–coil copolymers

We investigate the morphology and kinetics of microphase separation in rod–coil diblock copolymers where each chain consists of a stiff rod block and a flexible coil block. A simplified phenomenological model system is introduced, which is coarse grained in terms of the local concentration difference between the two blocks and the local director field of the rod part. Computer simulations of this set of time-evolution equations in two dimensions reveal that the elastic energy in the rod-block-rich domains affects drastically the domain structures formed in the course of microphase separation. The effects of the external electric field are investigated to examine the domain stability and control the domain morphology. Our recent study of morphological transitions in three dimensions for coil–coil copolymers is also briefly described.

Morphology of microphase separated domains in rod-coil copolymer melts.

We investigate the morphology of microphase separated domains in diblock copolymers where each chain consists of a stiff rod block and a flexible coil block. A simplified phenomenological model system is introduced, which is coarse-grained in terms of the local concentration difference between the two blocks and the local director field of the rod part. Computer simulations of this set of time-evolution equations in two dimensions show in the weak segregation regime that the elastic energy in the rod-block rich domains affects drastically the structures of microphase separated domains. A coil-to-rod transition is incorporated into the model system to examine the elastic and anisotropic effects. The effects of the external electric field are also investigated to control the domain morphology.

Microphase separation in rod-coil copolymers

We investigate the morphology and kinetics of microphase separation of diblock copolymers where each chain consists of a rod-like block and a flexible block. Simplified phenomenological model systems are introduced, which are coarse-grained in terms of the local concentration of blocks and the local director field of the rod part. Computer simulations of this set of time–evolution equations in two dimensions show that existence of the rod blocks drastically affects the structures of microphase-separated domains due to the elastic energy in the rod-block-rich domains.

The kinetics and morphology of phase-separating copolymer mixtures

Copolymers consisting of incompatible monomer blocks undergo a microphase separation at low temperatures. Various spatially periodic domain structures appear in the final equilibrium. A mixture of copolymers provides us with more variety of domain morphology since both microphase and macrophase separations take place simultaneously. We will describe some recent results of computer simulations of copolymer - homopolymer and copolymer - copolymer mixtures in two dimensions emphasizing a new type of pattern and a morphological transition of domains. It is also shown that the kinetics of phase separation can depend strongly on the domain morphology.

Morphology of Binary Mixtures Which Undergo Phase Separation during Chemical Reactions

When a chemical reaction such as \(A \rightleftharpoons B\) takes place simultaneously with a macrophase separation, mesoscopic structures similar to the patterns emerging during microphase separation appear. Since in a chemical system we can easily control the concentrations of the two species and reaction rates and so on, a greater variety of domain morphology is expected. We demonstrate some of the new morphologies by computer simulations.

Target Patterns in Phase Separation Induced by Cross-Linking

We introduce a quite simple model for a phase-separating binary mixture where one of the components is cross-linked. It is shown by computer simulations that target patterns are generated. We use a Cahn-Hilliard equation with a bulk free energy density which varies as a molecular weight changes with time. Target patterns are obtained in the following way. We first quench the system, having an off-critical composition, into a spinodal region, and find that disconnected droplets emerge in the system. With cross-linking one of the components, the phase diagram of the system shifts to a location where a bicontinuous structure is formed. As a result, target patterns grow from the droplets without any additional nuclei.

POLYMERIZATION-INDUCED PHASE SEPARATION OF POLYMER-DISPERSED LIQUID CRYSTAL

Abstract Polymerization-induced phase separation in polymer-dispersed liquid crystal is studied by computer simulations in two dimensions. The domain morphology resulting from phase separation is investigated by solving the couple set of equations for the local volume fraction and the nematic order parameter, taking into account the viscoelastic effects and gelation due to polymerization. Comparing the morphology of phase separation by temperature quench, it is shown that the viscoelastic effects and gelation enable the polymer-rich phase to form a stable interconnected domain even when the polymer component is minority.