Structure transitions in oblate nematic droplets.

We consider the structure transitions in oblate supramicrometer nematic droplets related to reorientation of the line defect in the electric field. These transitions can be used in optical devices based on polymer dispersed liquid crystal materials with high contrast ratio. We suggest a simple method for determination of director distribution in nematic droplets of an arbitrary shape with surface interaction and in the presence of constant electric field. Point and linear defects are taken into account. This method does not require any presuppositions about symmetry of the director distribution. The elasticity continuum theory is treated with Monte Carlo annealing on a simple lattice. A special triangulation-based technique is applied for accurate representation of the droplet boundaries. The method is tested on 5CB material.

Features in coherent transmittance of a monolayer of particles.

Coherent and incoherent transmittance values of a monolayer of particles are considered. Such a monolayer is a set of particles whose centers are located in the same plane. We set forth the conditions for the effect of coherent-transmittance quenching, which takes place as a result of the interference between incident and forward-scattered waves. Using the single-scattering approximation we determined size parameters and particle refractive indexes for this interference effect in the case of identical isotropic spherical particles. The influence of polydispersity and the fine structure of light-scattering characteristics on the quenching effect has been estimated. It is shown that the polydispersity destroys this interference effect only at large widths of particle-size distribution functions. The influence of multiple scattering on this effect is considered in the quasi-crystalline approximation. Multiple scattering results in increasing size parameters and decreasing particle concentration at which coherent transmittance quenching takes place in comparison with the case of single scattering. Our theoretical results for suspensions of latex particles in water are in fairly good agreement with the experimental results.

Passage of light through a dispersion medium with a high concentration of discrete inhomogeneities: experiment.

The passage of light through dispersion layers consisting of large weakly absorbing scatterers has been investigated. Measurements of the transmittance and the angular structure of scattered radiation have been made. The dependence of these characteristics on the thickness and the concentration of scatterers has been analyzed.

Influence of the director field structure on extinction and scattering by a nematic liquid-crystal droplet.

On the basis of calculations under the discrete dipole approximation and a proposed extended model of nested ellipsoids for bipolar droplets, the changes in optical properties of a spherical liquid-crystal droplet, caused by a change in director configuration under the influence of an external field, have been considered.

Light transmission by a monolayer of particles: comparison of experimental data with calculation as a single-scattering approximation.

The laws of light transmission by particle monolayers are investigated. The results of measurement of coherent transmission for monolayers formed by large nonabsorbing particles are presented. The obtained results are compared to the calculation in the single-scattering approximation. Good agreement between experimental and calculated data is shown.

Angular structure of radiation scattered by monolayers of particles: experimental study.

An experimental study has been made of the angular structure of radiation scattered by monolayers of large nonabsorbing particles. We have investigated three media exhibiting different light-scattering properties: monodisperse polyvinyl toluene latex particles of 3.75-mum diameter suspended in water, polydisperse rice starch particles with a mean diameter of 6.4 mum suspended in water, and a mixture of ethyl and benzoic alcohols. It is shown that for large particles the structure of scattered radiation can be described in a single-scattering approximation. Analysis of the influence of polydispersity and the relative refractive index of particles on the intensity scattered by the monolayer has been performed.