Abstract
The director fields adopted by nematic liquid crystals (LCs) that are confined by the surface to form long, thin droplets are investigated using polarising optical microscopy. Samples are produced by de-wetting of the LC on a surface patterned with alternating high-surface energy and low-surface energy stripes of 10–30 μm width. The droplets obtained are expected to adopt a profile which is that of a longitudinal section of a cylinder and, as this suggests, the director fields observed are variants in the case where the LC is constrained in a cylindrical capillary or fibre. Hence, when there is normal anchoring at the air interface, the textures observed are related to the well-known escaped radial texture (for the nematic LC mixture E7) or plane polar texture (for the LC mixture MLC6609). More surprising is the observation that the nematic LC mixture MLC7023, which is anchored in a planar or tilted manner at the air interface, also gives what appears to be an escaped radial director field. As an exploration of the possibility of using these systems in creating sensors, the effects of adding a chiral dopant and of adding water to the substrates are also investigated.
Highlights
Understanding how the director fields of liquid crystals (LCs) respond to confinement in thin films, fibres, droplets, etc., is fundamental to our use of these materials in displays [1,2,3], in optical compensating films [4], in the production of high-tensile strength fibres [5,6,7] and in chemical and biological sensors [8,9,10]
We examined the case of long, thin droplets of columnar phases of discotic LCs where the de-wetting occurs when the sample is heated into its isotropic phase [26]
We report a preliminary investigation of some calamitic nematic LCs
Summary
Understanding how the director fields of liquid crystals (LCs) respond to confinement in thin films, fibres, droplets, etc., is fundamental to our use of these materials in displays [1,2,3], in optical compensating films [4], in the production of high-tensile strength fibres [5,6,7] and in chemical and biological sensors [8,9,10]. When a planar surface is patterned with alternating hydrophilic and hydrophobic stripes that are 10–30 μm wide, liquids added to the surface de-wet onto the hydrophilic (high-surface energy) areas, giving an array of long, thin droplets. At this scale, the behaviour of droplets is dictated by the surface tension, giving droplet profiles that are longitudinal sections of a cylinder (Figure 1). The behaviour of droplets is dictated by the surface tension, giving droplet profiles that are longitudinal sections of a cylinder (Figure 1) These are hemi-cylindrical in the case when the contact angle is 90◦ (Figure 1b) [26]
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