Nematic liquid crystal alignment on chemical patterns

Abstract

Patterned Self-Assembled Monolayers (SAMs) promoting both homeotropic and planar degenerate alignment of 6CB and 9CB in their nematic phase, were created using microcontact printing of functionalised organothiols on gold films. The effects of a range of different pattern geometries and sizes were investigated, including stripes, circles and checkerboards. Evanescent Wave Ellipsometry was used to study the orientation of the liquid crystal (LC) on these patterned surfaces during the isotropic-nematic phase transition. Pretransitional growth of a homeotropic layer was observed on 1 µm homeotropic aligning stripes, followed by a homeotropic mono-domain state prior to the bulk phase transition. Accompanying Monte-Carlo simulations of LCs aligned on nano-patterned surfaces were also performed. These simulations also showed the presence of the homeotropic mono-domain state prior to the transition. * Electronic address: s.d.evans@leeds.ac.uk

Liquid crystal alignment induced by micron-scale patterned surfaces

“…In this case, one must resort to the Landau-de Gennes Q-tensor theory in conjunction with numerical methods if defects are to be treated accurately [32][33][34]. In cases with sufficiently small patterns, molecular simulations have also been used to examine the anchoring effect and LC orientation near the patterns [11,35].…”

“…An alternative approach that has received some interest involves patterning the aligning surfaces with either topographic relief features or flat micron-scale regions imposing different LC orientations, e.g., checkerboard or stripe patterns alternating between horizontal and vertical alignment. Techniques used for patterning the surfaces include AFM inscription [5], photolithography [6], nanoimprinting [7], and micro and nanoprinting of chemical alignment patterns [8][9][10][11].…”

Nematic films at chemically structured surfaces

“…[22][23][24][25] and experimentally in refs. [26][27][28]. Theoretical analysis predicted the existence of both orientationally uniform and non-uniform nematic textures in a semi-infinite geometry depending on the pattern geometry and anchoring strengths.…”

“…Theoretical analysis predicted the existence of both orientationally uniform and non-uniform nematic textures in a semi-infinite geometry depending on the pattern geometry and anchoring strengths. When the nematic LC is confined between two substrates, with one micropatterned, it is possible to create non-uniform LC textures in the cell [28,29]. Such micro-textures consist of alternating uniform and hybrid aligned nematic configurations (planar at one and perpendicular at the other substrate) and are used as low cost, easy-to-fabricate LC diffraction gratings [29] -optical devices operating in a transmission mode.…”

Anomalous uniform domain in a twisted nematic cell constructed from micropatterned surfaces

“…In the present work, we use a striped surface made by microcontact printing of self assembled monolayers (SAMs) of ω-functionalised alkanethiols [5,6,7] on gold to demonstrate that this elastic-anisotropy mechanism is suciently strong to permit the construction of a twisted nematic cell. Since the homeotropic-planar mark-space ratio is 1:1, the cells have a high tilt angle (∼ 45…”