Thermal optical non-linearity of nematic mesophase enhanced by gold nanoparticles--an experimental and numerical investigation.

In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n2, is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity.

Lifting degeneracy in nematic liquid crystal viscosities with a single optical measurement.

The viscosity of complex, anisotropic fluids, such as liquid crystals or their colloidal suspensions, is characterized by a number of coefficients. Methods to measure them are, typically, sensitive only to their particular combinations, hence unable to determine them individually. Using an Ericksen-Leslie model and propagation of light through aligned layers of such materials, we show theoretically and verify experimentally how this degeneracy can be lifted by exploiting both the amplitude and frequency of the voltage applied to the cell as control parameters.

Multiscale models of colloidal dispersion of particles in nematic liquid crystals.

We use homogenization theory to develop a multiscale model of colloidal dispersion of particles in nematic liquid crystals under weak-anchoring conditions. We validate the model by comparing it with simulations by using the Landau-de Gennes free energy and show that the agreement is excellent. We then use the multiscale model to study the effect that particle anisotropy has on the liquid crystal: spherically symmetric particles always reduce the effective elastic constant. Asymmetric particles introduce an effective alignment field that can increase the Fredericks threshold and decrease the switch-off time.