arXiv subjects

Noel A. Clark

Publications and source records attributed to Noel A. Clark.

42 records · Page 3Linked to original sources

arXiv2002

Phase Behavior of Bent-Core Molecules

Recently, a new class of smectic liquid crystal phases (SmCP phases) characterized by the spontaneous formation of macroscopic chiral domains from achiral bent-core molecules has been discovered. We have carried out Monte Carlo simulations of a minimal hard spherocylinder dimer model to investigate the role of excluded volume interations in determining the phase behavior of bent-core materials and to probe the molecular origins of polar and chiral symmetry breaking. We present the phase diagram as a function of pressure or density and dimer opening angle $ψ$. With decreasing $ψ$, a transition from a nonpolar to a polar smectic phase is observed near $ψ= 167^{\circ}$, and the nematic phase becomes thermodynamically unstable for $ψ< 135^{\circ}$. No chiral smectic or biaxial nematic phases were found.

cond-mat.stat-mech↗

arXiv2001

Self-assembly in Lyotropic Chromonic Liquid Crystals

We have developed a class of idealized models of chromonic molecules which are miscible in water, but which can form aggregates which in turn organize into lyotropic liquid crystal (LC) phases. By carrying out Monte Carlo simulation in a binary mixture of model chromonic and water molecules, we have studied the effect of concentration and molecular shape on the nature of resulting mesophases. We have also computed the free energy associated with the formation of chromonic columnar aggregates by umbrella sampling. Our free energy computation helps us to verify the isodesmic behavior which is characteristic of chromonic systems. For isodesmic behavior the addition of each chromonic molecule to the columnar aggregates is accompanied by a constant free energy increment and the net free energy decreases with increasing column length.

cond-mat.stat-mech↗

arXiv2001

Induced Anticlinic Ordering and Nanophase Segregation of Bow-Shaped Molecules in a Smectic Solvent

Recent experiments indicate that doping low concentrations of bent-core molecules into calamitic smectic solvents can induce anticlinic and biaxial smectic phases. We have carried out Monte Carlo (MC) simulations of mixtures of rodlike molecules (hard spherocylinders with length/breadth ratio $L_{\rm rod}/D = 5$) and bow- or banana-shaped molecules (hard spherocylinder dimers with length/breadth ratio $L_{ban}/D = 5$ or 2.5 and opening angle $ψ$) to probe the molecular-scale organization and phase behavior of rod/banana mixtures. We find that a low concentration (3%) of $L_{ban}/D = 5$ dimers induces anticlinic (SmC$_A$) ordering in an untilted smectic (SmA) phase for $100^\circ \le ψ< 150^\circ$. For smaller $ψ$, half of each bow-shaped molecule is nanophase segregated between smectic layers, and the smectic layers are untilted. For $L_{ban}/D = 2.5$, no tilted phases are induced. However, with decreasing $ψ$ we observe a sharp transition from {\sl intralamellar} nanophase segregation (bow-shaped molecules segregated within smectic layers) to {\sl interlamellar} nanophase segregation (bow-shaped molecules concentrated between smectic layers) near $ψ= 130^\circ$. These results demonstrate that purely entropic effects can lead to surprisingly complex behavior in rod/banana mixtures.

cond-mat.stat-mech↗

arXiv1996

Self-Consistent Model of Annihilation-Diffusion Reaction with Long-Range Interactions

We introduce coarse-grained hydrodynamic equations of motion for diffusion-annihilation system with a power-law long-range interaction. By taking into account fluctuations of the conserved order parameter - charge density - we derive an analytically solvable approximation for the nonconserved order parameter - total particle density. Asymptotic solutions are obtained for the case of random Gaussian initial conditions and for system dimensionality $d \geq 2$. Large-t, intermediate-t and small-t asymptotics were calculated and compared with existing scaling theories, exact results and simulation data.

cond-mat↗

arXiv1996

Scaling Model of Annihilation-Diffusion Kinetics for Charged Particles with Long-Range Interactions

We propose the general scaling model for the diffusio n-annihilation reaction $A_{+} + A_{-} \longrightarrow \emptyset$ with long-range power-law i nteractions. The presented scaling arguments lead to the finding of three different regimes, dep ending on the space dimensionality d and the long-range force power e xponent n. The obtained kinetic phase diagram agrees well with existing simulation data and approximate theoretical results.

cond-mat↗

arXiv1996

Self-Consistent Model of Polymerization-Induced Phase Separation

We propose an exactly solvable self-consistent kinetic model of polymerization-induced phase separation (PIPS) via spinodal decomposition. Using modified Cahn-Hilliard and Glotzer-Coniglio theories for early and late stages of spinodal decomposition, we find scaling regimes and compare the obtained results with existing experimental and theoretical information on PIPS kinetics, finding a good qualitative agreement.

cond-mat↗