Electrical reorientation of liquid crystal molecules inside cylindrical pores for photonic device applications

Rheological Properties of Liquid Crystals in Porous Polymer Films with Submicron Sizes of Pores

“…It can be used for different explanations of our experimental results. In particular, the computer simulation of ER configuration of NLC, formed inside pores [15] and marked as (d) in Fig. 5, has shown that weak anchoring effects have to be taken into account for typical values of the anchoring strength and small pore's diameters.…”

Nematic Liquid Crystal Confined in Electrochemically Etched Porous Silicon: Optical Characterization and Applications in Photonics

“…The director field in the ER configuration was calculated using the Frank's free energy approach. We have used the following constants for E7 (Crawford et al, 1992;Leonard et al, 2000;Tkachenko et al, 2008]: K 11 = 11.1 pN; K 33 = 17.1 pN; K 24 = 28.6 pN and the dispersion curves for ordinary and extraordinary indices from . According to (Crawford et al, 1992;Leonard et al, 2000), the surface anchoring strength W for the E7 in supramicrometer silicon pores is estimated to be 10 -5 J/m 2 .…”

“…First of all, the effective refractive index n LC of liquid crystal in pores depends on the spatial distribution of the local director L. In the nematic phase, the LC director field depends on the interplay between molecular surface anchoring, elastic energies of the liquid crystal, and forces caused by external fields, if any. Here the director field of the nematic mixture E7 confined in cylindrical pores is calculated using the Frank's free energy approach (Crawford et al, 1992;Tkachenko et al, 2008). If there is no external influence, the free energy F of the confined nematic is given by (Crawford et al, 1992):…”

“…When the director field Ω(r) of LC inside the silicon pore is found, the effective dielectric permittivity and refractive index of the nematic LC in a cylindrical pore is calculated by the formula (Tkachenko et al, 2008):…”

“…While electric field is applied to a multilayer PSi filled with the liquid crystal the value of n LC goes down causing the decrease of the effective refractive index of each porous layer. As an example, we simulated spectra of the multilayer structure containing a microcavity sandwiched between two PSi distributed Bragg reflectors with alternating layers of 50% and 80% porosity, filled with E7 and tuned by the external electric field (Tkachenko et al, 2008). Shift of the microcavity resonance versus electric field is shown in Fig.…”