Abstract
ABSTRACT Combining liquid crystals (LCs) with well-designed anchoring patterns at the substrates offers tremendous potential for the development of functional electro-optic devices or stimuli-responsive actuators. Photo-alignment techniques nowadays allow an almost arbitrary control over the surface anchoring and this flexibility is used to design highly efficient flat optical LC components with different functionalities. Part of this research, dealing with nematic and chiral nematic LC between substrates with patterned azimuthal anchoring, is reviewed here. The focus is on understanding the self-assembly of complex structures, steered by an interplay between surface anchoring and LC elasticity. Additional insight into the LC bulk behaviour is obtained by comparing experimental results with numerical simulations of the director configuration. Periodic anchoring patterns with azimuthal rotation at the top and bottom substrate are studied, as well as ring-shaped alignment patterns with a 180° or 360° azimuthal rotation in a confined region in space. Different combinations of anchoring patterns at the top and bottom substrates are investigated and in addition to nematic liquid crystal (NLC), also short and long-pitch chiral nematic liquid crystal (CLC) is considered.
Highlights
Research on liquid crystals (LCs) ranges from fundamen tal science to applied research with practical applica tions in different domains [1,2,3]
The range of applications in this research domain is extended, but here we focus on patterned LC config urations to create so-called flat optical components, that are only a few micrometre thick but demonstrate excel lent optical performance
We recently demon strated that when a lithographically patterned substrate with a well-chosen topographical period is combined with chiral nematic liquid crystal (CLC), this can lead to voltage-induced directional growth of cholesteric fingers or a uniform lying helix-like structure [32,33]
Summary
Research on liquid crystals (LCs) ranges from fundamen tal science to applied research with practical applica tions in different domains [1,2,3]. We recently demon strated that when a lithographically patterned substrate with a well-chosen topographical period is combined with CLC, this can lead to voltage-induced directional growth of cholesteric fingers (long-pitch CLC) or a uniform lying helix-like (for short pitch CLC) structure [32,33] This behaviour was not induced by the topogra phy (height difference) of the surface, but rather by the difference in anchoring that is obtained for the ITO-coated areas and the areas covered by e-beam resist. Different illumination methods exist to create variations in the azimuthal anchoring at the substrate [7,17,46,47,48] and we use interference illumination or structured illumina tion with the help of a blue laser setup with a spatial light modulator (SLM) Alternative methods such as direct write illumination, plasmonic patterning, etc. Alternative methods such as direct write illumination, plasmonic patterning, etc. have been reported in the literature and the preferred illumination method depends on the envisioned application
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