Structure transitions in oblate nematic droplets

Abstract

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.

Formation and field-driven dynamics of nematic spheroids

“…which includes elastic energy terms that quantify the nematic response to orientational deformations of splay k 11 , twist k 22 , bend k 33 , and saddle-splay k 24 . Many past simulation studies of elliptic nematic capillaries and ellipsoidal droplets 14,17,19 use this simplified model despite its inability to accurately capture nanoscale defects in nematic order, called disclinations. 25 Disclinations correspond to singularities in the nematic director n, and are therefore also regions of high biaxial nematic order (S, P > 0), as opposed to isotropic regions of disorder (S = P = 0).…”

“…10,11 While a significant body of past mesoscale simulation work exists for cylindrical nematic capillaries 12,13 and spherical droplets, [14][15][16] elliptic or ellipsoidal domains have been far less studied. [17][18][19][20] Furthermore, of this work, most use theoretical models which are unable to accurately capture nematic defects and phase transition. Only recently have simulations been performed which capture nematic dynamics, 21 as opposed to just determining equilibrium states.…”

Field-driven dynamics of nematic microcapillaries

“…However, direct experimental observation of LC internal structure and dynamics for PDLC composites is challenging due to the length (nm − µm) and time (ns − µs) scales involved in LC dynamics. Simulation studies [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], however, have shed light on a far more rich landscape of internal structure than what is observable through experimentation. Over the past two decades, simulation-based analysis has been used with increasing success, mainly focusing on cylindrical and spherical domains.…”

“…Lattice-based simulations [5][6][7][8] are able resolve sub-micron domains and have mainly been applied to study the effects of sub-micron cylindrical confinement where geometry and anchoring affects the stability of the nematic phase. However, continuum simulations [12][13][14][15][16][17][18][19][20][21][22][23][24] have been able to overcome the length and timescales required to simultaneously capture defect dynamics (nanoscale) and domain shape (≥ µm).…”

Orientational ordering of Janus colloids in cholesteric liquid crystals

“…The dimensionless surface anchoring strength at the spherical particle μ = W d 2K 11 was set to 200 to simulate the strong anchoring. The ratio between elasticity constants was set to K 11 : K 22 : K 33 = 1 : 0.70 : 1.25, and the defects energy F de f was calculated by the method considered in 17 , where f core line was set to 4.7 (K 11 +K 22 +K 33 ) 3 to simulate E8 + 20% CB15 cholesteric at the temperature 10 K below the melting point 19 . The system was rendered in 48 × 48 × 48 lattice, and both tilt θ and azimuthal ϕ angles defining the orientation of a colloid particle were changed with a step of 10 • .…”