Hao-Wen Chiu

EQUILIBRIUM PHASE BEHAVIOR OF NEMATIC MIXTURES

A phenomenological model for predicting phase diagrams of a binary nematic mixture containing side chain liquid crystalline polymers and/or low molar mass liquid crystals has been proposed by combining Flory–Huggins free energy of isotropic mixing and Maier–Saupe free energy for nematic ordering of the nematogens. Two orientational order parameters, s1 and s2, of the two components in the mixtures having two different clearing temperatures are taken into consideration in the calculation. The Flory–Huggins interaction parameter, χ, and the nematic interaction parameter of the Maier–Saupe theory, ν11 and ν22, are assumed to be functions of inverse absolute temperature. Further the cross‐nematic interaction is assumed to be proportional to the square root of the product of the nematic interaction parameters of the two mesogens, i.e., ν12=c (ν11⋅ν22)1/2. The theory predicts a variety of phase diagrams depending on a single parameter, c, which is a measure of a relative strength of interaction between two diss...

Morphology development during polymerization-induced phase separation in a polymer dispersed liquid crystal

Abstract To elucidate the emergence of liquid crystal (LC) domains during polymerization induced phase separation in a polymer dispersed liquid crystal (PDLC), numerical simulation has been performed by incorporating the kinetics of crosslinking reaction into the time-dependent Ginzburg–Landau (TDGL-Model C) equations in conjunction with the combined Flory–Huggins (FH)/Maier–Saupe (MS) free energies. The TDGL-Model C basically consists of two coupled equations in which a conserved compositional order parameter (i.e. the volume fraction) is coupled with a non-conserved orientational order parameter of the LCs. Of particular interest is the influence of nematic ordering on the emergence of domain morphology that shows a strong dependence on curing temperatures and compositions, displaying a rich variety of patterns.

Phase separation behaviour in blends of isotactic polypropylene and ethylene-propylene diene terpolymer

Miscibility and phase separation behaviour in blends of isotactic polypropylene (iPP) and ethylene-propylene diene terpolymer (EPDM, ethylene content 70%) have been examined by means of depolarized light scattering, polarizing optical microscopy, differential scanning calorimetry and dynamic mechanical methods. A cloud point phase diagram was established by means of light scattering after eliminating the influence of iPP crystal melting on liquid-liquid phase separation of iPP/EPDM blends. A lower critical solution temperature (LCST) was observed above the crystallization temperature, but below the melting temperature of iPP. This LCST is thermally reversible, so long as crystallization does not occur in its vicinity. The coupling between the crystal melting and liquid-liquid phase separation has been examined. Crystallization-induced phase separation and morphology development during crystallization of iPP have been investigated.

Theoretical investigation on dynamics of photopolymerization-induced phase separation and morphology development in nematic liquid crystal/polymer mixtures

A theoretical investigation of the dynamics of photopolymerization-induced phase separation (PIPS) and morphology development in a nematic liquid crystal (LC) polymer network mixture has been undertaken by incorporating photopolymerization kinetics into the coupled time-dependent Ginzburg-Landau (TDGL–Model C) equations. The simulation on the spatio-temporal evolution of the coupled LC concentration and orientation order parameters reveals that both morphological and scattering patterns for the orientation order parameter initially lag behind those of the concentration order parameter. However, the two fields evolve to the same spatial topologies with the progression of time. The PIPS dynamics is characterized only by the late stage of phase separation. We also observed a subtle change in the curvature of the growth curve associated with the onset of nematic ordering. The growth behavior and the simulated morphology consisting of LC droplets dispersed in a matrix of polymer appears the same for all compos...

Spatio-Temporal Growth of Nematic Domains in Liquid Crystal Polymer Mixtures

Dynamics of phase separation and morphology development in mixtures of a low molar mass liquid crystal (LC) and a polymer have been investigated theoretically in comparison with experimental results. In the theoretical model, the combined free-energy densities of Flory–Huggins theory for isotropic mixing and Maier–Saupe theory for nematic ordering have been incorporated into the time-dependent Ginzburg–Landau equation (type C). The temporal evolution of the structure factor and the emergence of phase-separated liquid crystal domains have been simulated on the basis of an explicit central difference method based on a square lattice (128×128) with a periodic boundary condition. Of particular interest is the observed plateau (or inflection) region in the growth dynamic curve, which may be attributed to the breakdown of the interconnected domains caused by the nematic ordering. This unique behavior has been verified experimentally in terms of the growth of structure factor following several temperature quench...

Phase diagrams of a binary smectic-A mixture

A variety of smectic phase diagrams involving smectic-isotropic and smectic-nematic-isotropic transitions have been calculated based on a combination of Flory–Huggins (FH) theory for isotropic mixing and Maier–Saupe–McMillan (MSM) theory for smectic-A ordering of liquid crystals (LC). To describe the mesophase transitions, two nematic order parameters and two smectic order parameters have been coupled through the normalized orientation distribution and partition functions. Flory–Huggins interaction parameter (χ) for isotropic mixing and the coupling term involving the nematic interaction parameter (ν) and the McMillan smectic interaction parameter (α) for phase transitions of liquid crystals have been incorporated in the calculation. The predictive capability of the present combined FH/MSM model for determining the coexistence regions of a binary smectic-A mixture has been demonstrated by critically testing with a reported smectic phase diagram.

Effect of Molecular Weight on Miscibility Phase Diagrams in Mixtures of Polymer and Liquid Crystals

Abstract Phase diagrams in mixtures of side chain liquid crystalline polymers (SCLCP) and liquid crystals (LC) have been computed by combining Flory-Huggins (FH) theory for isotropic mixing and Maier-Saupe (MS) theory for nematic ordering. In the calculation, two orientational order parameters with two different clearing transitions are taken into consideration for nematic mixtures. In the case of flexible homopolymer and liquid crystal mixtures, only one orientational order parameter with one nematic-isotropic transition is necessary, he effects of molecular weight of matrix polymer on phase diagrams of polymer/liquid crystal mixtures have been investigated using polymethyl methacrylate having varying molecular weights as matrix resins.

Phase Equilibria of a Nematic and Smectic-A Mixture

A phase diagram of a mixture consisting of nematic and smectic liquid crystals has been calculated self-consistently by combining Flory–Huggins (FH) theory for isotropic mixing and Maier–Saupe–McMillan (MSM) theory for smectic-A ordering. However, the MSM theory can be deduced to the original Maier–Saupe (MS) theory for nematic ordering. To describe the phase transitions involving induced smectic phase and nematic + smectic equilibrium, two nematic and two smectic order parameters for the nematic/smectic mixtures have been coupled through the normalized partition function and the orientation distribution function. Self-consistent numerical solution has been sought in establishing nematic/smectic phase diagrams involving (i) phase separation between nematic and smectic liquid crystals and (ii) occurrence of induced smectic in a nematic/smectic mixture. The predictive capability of this combined FH/MSM theory has been tested critically with a reported phase diagram of a nematic/smectic liquid-crystal mixtur...

Miscibility Phase Diagrams of the Mixtures of Side-on Side Chain Liquid Crystalline Polymers and Low Molar Mass Liquid Crystals

Abstract Miscibility phase diagrams of mixtures of a side-on side-chain liquid crystalline polymer (s-SCLCP) and low molar mass liquid crystals have been investigated experimentally and theoretically. The theoretical calculation on equilibrium phase diagrams of binary nematic mixtures involves a combination of the Flory-Huggins (FH) free energy for isotropic mixing in conjunction with the Maier-Saupe (MS) free energy for nematic ordering of the mesogenic units. This combined FH-MS theory predicts a variety of phase diagrams depending on relative strength of cross-interaction between two dissimilar mesogens to that in the same species. The s-SCLCP synthesized is polyacrylate with a mesogenic side group connected by a butyl spacer. The temperature-composition phase diagrams of the mixtures of s-SCLCP and eutectic low molar mass liquid crystal (E44 and E48) have been established by a cloud point method. The calculated phase diagrams are found to accord well with the experimental phase diagrams.