Photopolymerization-Induced Directional Crystal Growth In Reactive Mixtures,
2014
University of Akron Main Campus
Photopolymerization-Induced Directional Crystal Growth In Reactive Mixtures, Soo Jeoung Park, Pankaj Rathi, Thein Kyu
Thein Kyu
Photopolymerization-induced crystallization has been demonstrated in blends of polyethylene oxide-diacrylate at temperatures above the depressed melting temperature of the crystalline component. Upon exposure to ultraviolet irradiation, the melting transition curve moves upward and eventually surpasses the reaction temperature, thereby inducing phase separation as well as crystallization. The present paper demonstrates the occurrence of directionally solidified interface morphologies of polymer crystals subjected to a photointensity gradient. The epitaxially grown seaweed or degenerate structures were observed at the circumference (low-intensity region) while the dense branched spherulites developed at the core high-intensity region.
Effect Of Trans-Cis Photoisomerization On Phase Equilibria And Phase Transition Of Liquid-Crystalline Azobenzene Chromophore And Its Blends With Reactive Mesogenic Diacrylate,
2014
Kent State University - Kent Campus
Effect Of Trans-Cis Photoisomerization On Phase Equilibria And Phase Transition Of Liquid-Crystalline Azobenzene Chromophore And Its Blends With Reactive Mesogenic Diacrylate, Namil Kim, Quan Li, Thein Kyu
Thein Kyu
Photoisomerization-induced phase transition of neat liquid-crystalline azobenzene chromophore (LCAC) and its effect on phase diagrams of its mixtures with reactive mesogenic diacrylate monomer (RM257) have been investigated experimentally and theoretically. Upon irradiation with ultraviolet light, the nematic phase of LCAC transformed to isotropic, while the crystal phase showed corrugated textures on the surface (i.e., ripples). The phase-transition temperatures and corresponding morphologies of the blends have been investigated by means of differential scanning calorimetry and optical microscopy. A theoretical phase diagram of a binary nematic and crystalline system was constructed by self-consistently solving the combined free energies of Flory-Huggins, Maier-Saupe, and …
Theory And Computation Of Photopolymerization-Induced Phase Transition And Morphology Development In Blends Of Crystalline Polymer And Photoreactive Monomer,
2014
University of Akron Main Campus
Theory And Computation Of Photopolymerization-Induced Phase Transition And Morphology Development In Blends Of Crystalline Polymer And Photoreactive Monomer, Pankaj Rathi, Thein Kyu
Thein Kyu
A hypothetical phase diagram of a crystalline polymer/photoreactive monomer mixture has been calculated on the basis of phase field (PF) free energy of crystal solidification in conjunction with Flory-Huggins (FH) free energy of liquid-liquid demixing to guide the morphology development during photopolymerization of poly(ethylene oxide)/triacrylate blend. The self-consistent solution of the combined PF-FH theory exhibits a crystalline-amorphous phase diagram showing the coexistence of solid+liquid gap bound by the liquidus and solidus lines, followed by an upper critical solution temperature at a lower temperature. When photopolymerization was triggered in the isotropic region, i.e., slightly above the crystal melting transition temperatures, the …
Nucleation Initiated Spinodal Decomposition In A Polymerizing System,
2014
University of Akron Main Campus
Nucleation Initiated Spinodal Decomposition In A Polymerizing System, Thein Kyu, Jae Hyung Lee
Thein Kyu
Dynamics of phase separation in a polymerizing system, consisting of carboxyl terminated polybutadiene acrylonitrile/epoxy/methylene dianiline, was investigated by means of time-resolved light scattering. The initial length scale was found to decrease for some early periods of the reaction which has been explained in the context of nucleation initiated spinodal decomposition We have combined the Cahn-Hilliard kinetic equation and polymerization kinetics, and predicted the initial reduction of the length scale triggered by nucleation.
Crystal-Liquid Crystal Binary Phase Diagrams,
2014
University of Akron Main Campus
Crystal-Liquid Crystal Binary Phase Diagrams, P Dayal, Ra Matkar, Thein Kyu
Thein Kyu
We propose a new theoretical scheme for the binary phase diagrams of crystal-liquid crystal mixtures by a combination of a phase field model of solidification, the Flory-Huggins theory for liquid-liquid mixing and Maier-Saupe-McMillan (FH-MSM) model for nematic and smectic liquid crystal orderings. The phase field theory describes the crystal phase transition of anisotropic organic crystal and/or side chain liquid crystalline polymer crystals while the FH-MSM model explains isotropic, nematic and smectic-A phase transitions. Self-consistent calculations reveal several possible phase diagram topologies of the binary crystal-liquid crystal mixtures. The calculated phase diagrams were found to accord well to the reported experimental …
Spatio-Temporal Growth Of Nematic Domains In Liquid Crystal Polymer Mixtures,
2014
University of Akron Main Campus
Spatio-Temporal Growth Of Nematic Domains In Liquid Crystal Polymer Mixtures, Hao-Wen Chiu, Thein Kyu
Thein Kyu
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 x 128) with a periodic boundary condition. Of …
Dynamics And Morphology Development In Electrospun Fibers Driven By Concentration Sweeps,
2014
University of Akron Main Campus
Dynamics And Morphology Development In Electrospun Fibers Driven By Concentration Sweeps, Pratyush Dayal, Thein Kyu
Thein Kyu
The present article describes the modeling and simulation of the dynamics of the electrospinning process coupled with the spatio-temporal evolution of fiber morphology driven by concentration sweeps. The electrospinning process has been modeled based on an array of beads connected by Maxwell's elements in a cylindrical shell to describe the force balance between Coulombic and viscoelastic forces at the surface of the jet. The phase separation dynamics has been calculated in the framework of the Cahn-Hilliard time-evolution equation by incorporating Flory-Huggins free energy for liquid-liquid demixing in conjunction with solvent evaporation through the fiber surface. The simulations based on the …
Equilibrium Phase-Behavior Of Nematic Mixtures,
2014
University of Akron Main Campus
Equilibrium Phase-Behavior Of Nematic Mixtures, Hao-Wen Chiu, Thein Kyu
Thein Kyu
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, s(1) and S-2, Of the two components in the mixtures having two different clearing temperatures are taken into consideration in the calculation. The Flory-Huggins interaction parameter, chi, and the nematic interaction parameter of the Maier-Saupe theory, nu(1) and nu(22), are assumed to be functions of inverse absolute temperature. Further the cross-nematic …
Effects Of Photointensity Gradient On Directional Crystal Growth In Blends Of Crystalline Polymer And Photoreactive Monomer Undergoing Photopolymerization-Induced Phase Transformation,
2014
University of Akron Main Campus
Effects Of Photointensity Gradient On Directional Crystal Growth In Blends Of Crystalline Polymer And Photoreactive Monomer Undergoing Photopolymerization-Induced Phase Transformation, Pankaj Rathi, Soo Park, Thein Kyu
Thein Kyu
Effects of light intensity gradient on development of intricate hierarchical morphology of semicrystalline polyethylene oxide (PEO) and photoreactive diacrylate (DA) blends undergoing photopolymerization-induced crystallization have been demonstrated experimentally and theoretically. The melting temperature of PEO was found to decline upon addition of DA monomer. A solid-liquid phase diagram has been established by self-consistently solving the combined phase field free energy of crystal solidification and Flory-Huggins (FH) free energy of liquid-liquid demixing. Dynamic calculations were performed using time-dependent Ginzburg-Landau (model C) equations by incorporating the combined phase field and FH free energy densities coupled with the photopolymerization kinetics. The spatiotemporal development …
Polymerization-Induced Phase-Separation In A Liquid-Crystal-Polymer Mixture,
2014
University of Akron Main Campus
Polymerization-Induced Phase-Separation In A Liquid-Crystal-Polymer Mixture, J. Y, Kim, C. H. Cho, P. Palffy-Muhoray, M. Mustafa, Thein Kyu
Thein Kyu
We have used light scattering to study the kinetics of polymerization-induced phase separation in a liquid-crystal-polymer mixture. The evolution of the structure factor is compared with scaling predictions for thermally quenched systems. We have also observed a cascading phenomenon where phase separated domains become unstable and undergo phase separation for a second time.
Spinodals In A Polymer-Dispersed Liquid-Crystal,
2014
University of Akron Main Campus
Spinodals In A Polymer-Dispersed Liquid-Crystal, Chungsea Shen, Thein Kyu
Thein Kyu
Thermodynamic phase equilibria of a polymer dispersed liquid crystal (PDLC) consisting ofmonomeric liquid crystals and a polymer have been investigated theoretically and experimentally.The equilibrium limits of phase separation as well as phase transition of a PDLC system werecalculated by taking into consideration the Flory–Huggins (FH) theory for the free energy of mixingof isotropic phases in conjunction with the Maier–Saupe ~MS! theory for phase transition of anematic liquid crystal. The correspondence between the Landau–de Gennes expansion and theMaier–Saupe theory was found and the coefficients were evaluated. The calculation based on thecombined FH-MS theory predicted a spinodal line within the coexistence of …
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. Ii. Temperature Jumps Above An Immiscibility Loop,
2014
University of Akron Main Campus
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. Ii. Temperature Jumps Above An Immiscibility Loop, Thein Kyu, Ds Lim
Thein Kyu
No abstract provided.
Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends,
2014
University of Akron Main Campus
Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends, Thein Kyu, Hw Chiu, Aj Guenthner, Y Okabe, H Saito, T Inoue
Thein Kyu
Numerical calculations reveal that the target and spiral growth patterns in spherulites can be generated from the time-dependent Ginzburg-Landau equations (model C) by coupling a conserved compositional order parameter and a nonconserved crystal ordering parameter. Of particular interest is that the periodic concentric rings (target) or the spirals at the spherulitic core remain stationary in both the crystal (orientational) ordering field and the concentration field. Another intriguing observation is that the growth of target and spiral spherulites occurs in a stepwise fashion in synchronism with the rhythmic energy dissipation during crystallization.
Phase Diagrams Of A Binary Smectic-A Mixture,
2014
University of Akron Main Campus
Phase Diagrams Of A Binary Smectic-A Mixture, Hao-Wen Chiu, Thein Kyu
Thein Kyu
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 (chi) for isotropic mixing and the coupling term involving the nematic interaction parameter (nu) and the McMillan smectic interaction parameter (alpha) for phase transitions of liquid crystals have been incorporated in the calculation. The predictive capability …
Phase Dissolution In A Liquid-Crystalline Polymer-Solution,
2014
University of Akron Main Campus
Phase Dissolution In A Liquid-Crystalline Polymer-Solution, T Kyu, Z. Ping, P. Mukherjee
Thein Kyu
No abstract provided.
Discrepancy In Determination Of Chi Parameters By Melting Point Depression Versus Small-Angle Neutron Scattering In Blends Of Deuterated Polycarbonate And Isotactic Poly(Methyl Methacrylate),
2014
University of Akron Main Campus
Discrepancy In Determination Of Chi Parameters By Melting Point Depression Versus Small-Angle Neutron Scattering In Blends Of Deuterated Polycarbonate And Isotactic Poly(Methyl Methacrylate), Thein Kyu, Rushikesh Matkar, Dong Lim, Chechian Ko
Thein Kyu
The discrepancy in the chi interaction parameters of deuterated polycarbonate/isotactic poly(methyl methacrylate) blends as determined by the melting point depression approach and the small-angle scattering technique is reported. We have modified the Flory diluent theory by removing the inherent assumption of complete rejection of the solvent from the crystal solid by taking into consideration the crystal-amorphous, amorphous-crystal, and crystal-crystal interactions. The discrepancy in chi values obtained by the two methods is discussed.
Phase-Separation Dynamics Of A Polymer-Dispersed Liquid-Crystal,
2014
University of Akron Main Campus
Phase-Separation Dynamics Of A Polymer-Dispersed Liquid-Crystal, Thein Kyu, I Ilies, M Mustafa
Thein Kyu
Phase separation in a polymer dispersed liquid crystal (PDLC), consisting of a main chain liquid crystal (E7) and polymethyl methacrylate (PMMA), was studied by means of light scattering and optical microscopy. The PMMA/E7 mixture exhibits an upper critical solution temperature (UCST), overlapping with a nematic-isotropic transition of the E7 liquid crystal. Several temperature quenches were undertaken by rapidly transferring the 60/40 PMMA/E7 from a single phase (95-degrees-C) to an unstable region (25, 35 and 45-degrees-C) and by subsequently monitoring the time-evolution of scattering profiles. The time-evolution of structure factor reveals a cross-over of a kinetic exponent from -0.33 to -0.6 …
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. I. Temperature Jumps Into An Immiscibility Loop,
2014
University of Akron Main Campus
Phase-Separation Dynamics Of Polycarbonate Polymethyl Methacrylate Blends. I. Temperature Jumps Into An Immiscibility Loop, Dong-Soo Lim, Thein Kyu
Thein Kyu
No abstract provided.
Spatiotemporal Growth Of Faceted And Curved Single Crystals,
2014
University of Akron Main Campus
Spatiotemporal Growth Of Faceted And Curved Single Crystals, Thein Kyu, Rujul Mehta, Hao-Wen Chiu
Thein Kyu
The spatiotemporal growth of single crystals in a crystalline polymer has been investigated theoretically based on a nonconserved time dependent Ginzburg-Landau equation (known as TDGL model A). In the description of the total free energy, a double-well local foe energy density signifying metastability of crystal ordering is combined with a nonlocal free energy term representing an interface gradient. The resulting nonlinear reaction diffusion equation after renormalization possesses a solitary wave property. Two-dimensional numerical calculations were performed to elucidate the faceted single crystal growth including square, rectangular, diamond-shaped, and curved single crystals. A three-dimensional simulation was also undertaken for the emergence …
Effect Of Thermal Transport On Spatiotemporal Emergence Of Lamellar Branching Morphology During Polymer Spherulitic Growth,
2014
University of Akron Main Campus
Effect Of Thermal Transport On Spatiotemporal Emergence Of Lamellar Branching Morphology During Polymer Spherulitic Growth, Haijun Xu, Wirunya Keawwattana, Thein Kyu
Thein Kyu
Spatiotemporal emergence of lamellar branching morphology of polymer spherulite has been investigated theoretically in the framework of a phase field model by coupling a crystal solidification potential pertaining to a nonconserved crystal order parameter with a temperature field generated by latent heat of crystallization. A local free-energy density having an asymmetric double well has been utilized to account for a first-order phase transition such as crystallization. To account for the polymorphous nature of polymer crystallization, the phase field order parameter of crystal at the solidification potential of the double-well local free-energy density is modified to be supercooling dependent. The heat …
