Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTopological Defects in Nematic Droplets of Hard Spherocylinders
375
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Using computer simulations we investigate the microscopic structure of the singular director field within a nematic droplet. As a theoretical model for nematic liquid crystals we take hard spherocylinders. To induce an overall topological charge, the particles are either confined to a two-dimensional circular cavity with homeotropic boundary or to the surface of a three-dimensional sphere. Both systems exhibit half-integer topological point defects. The isotropic defect core has a radius of the order of one particle length and is surrounded by free-standing density oscillations. The effective interaction between two defects is investigated. All results should be experimentally observable in thin sheets of colloidal liquid crystals.
rate research
Read More
We present computer simulations of long thin hard spherocylinders in a narrow planar slit. We observe a transition from the isotropic to a nematic phase with quasi-long-range orientational order upon increasing the density. This phase transition is intrinsically two dimensional and of the Kosterlitz-Thouless type. The effective two-dimensional density at which this transition occurs increases with plate separation. We qualitatively compare some of our results with experiments where microtubules are confined in a thin slit, which gave the original inspiration for this work.
Topological defects are one of the most conspicuous features of liquid crystals. In two dimensional nematics, they have been shown to behave effectively as particles with both, charge and orientation, which dictate their interactions. Here, we study twisted defects that have a radially dependent orientation. We find that twist can be partially relaxed through the creation and annihilation of defect pairs. By solving the equations for defect motion and calculating the forces on defects, we identify four distinct elements that govern the relative relaxational motion of interacting topological defects, namely attraction, repulsion, co-rotation and co-translation. The interaction of these effects can lead to intricate defect trajectories, which can be controlled by setting relevant timescales.
Hard spherocylinders (cylinders of length $L$ and diameter $D$ capped at both ends with two hemispheres) provide a suitable model for investigating entropy-driven, mesophase formations in real colloidal fluids that are composed of rigid rodlike molecules. We performed extensive Monte Carlo simulations of this model fluid for elongations in the range $3 leq L/D leq 5$ and up to $L/D = 20$, in order to investigate the relative importance of translational and orientational correlations allowing for the emergence of nematic or smectic order in the framework of the so-called residual multi-particle entropy (RMPE). The vanishing of this quantity, which includes the re-summed contributions of all spatial correlations involving more than two particles, signals the structural changes which take place, at increasing densities, in the isotropic fluid. We found that the ordering thresholds detected through the zero-RMPE condition systematically correlate with the corresponding phase-transition points, whatever the nature of the higher-density phase coexisting with the isotropic fluid.
We investigated the nematic to smectic transition undergone by parallel hard spherocylinders in the framework provided by the residual multi-particle entropy (RMPE) formalism. The RMPE is defined as the sum of all contributions to the configurational entropy of the fluid which arise from density correlations involving more than two particles. The vanishing of the RMPE signals the structural changes which take place in the system for increasing pressures. Monte Carlo simulations carried out for parallel hard spherocylinders show that such a one-phase ordering criterion accurately predicts also the nematic-smectic transition threshold notwithstanding the almost continuous character of the transition. A similar quantitative correspondence had been already noted in the case of an isotropic fluid of freely rotating hard spherocylinders undergoing a transition to a nematic, smectic or solid phase. The present analysis confirms the flexibility of the RMPE approach as a practical and reliable tool for detecting the formation of mesophases in model liquid-crystal systems.
We report numerical calculations of the concentration of interstitials in hard-sphere crystals. We find that, in a three-dimensional fcc hard-sphere crystal at the melting point, the concentration of interstitials is 2 * 10^-8. This is some three orders of magnitude lower than the concentration of vacancies. A simple, analytical estimate yields a value that is in fair agreement with the numerical results.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
