Recent results on structural properties and possible bio-sensing applications of planar liquid crystal films are reviewed.

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In this review article, we analyze recent progress in the application of liquid crystal-assisted advanced functional materials for sensing biological and chemical analytes. Multiple research groups demonstrate substantial interest in liquid crystal (LC) sensing platforms, generating an increasing number of scientific articles. We review trends in implementing LC sensing techniques and identify common problems related to the stability and reliability of the sensing materials as well as to experimental set-ups. Finally, we suggest possible means of bridging scientific findings to viable and attractive LC sensor platforms.

Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors.

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Determination of the content of environment polluting chemical agents is of significant importance. The goal of this study was the development of experimental approaches for detection of concentrations of surfaceactive molecules (surfactants) such as sodium dodecyl sulfate (SDS) and

Two-dimensional diffusion of a rhodamine 6G fluorescent tracer molecule at the n-decane/water interface was studied with all-atom molecular dynamics (MD) simulations. In agreement with experimental data, we find increased mobility of the tracer at the n-decane/water interfaces in comparison to its mobility in bulk water.Orientational ordering of water and n-decane molecules near the interface is observed, and may change the interfacial viscosity as suggested to explain the experimental data.However, the restricted rotational motion of the rhodamine molecule at the interface suggests that Saffman-Delbrück model may be a more appropriate approximation of rhodamine diffusion at n-decane/water interfaces, and, without any decrease in interfacial viscosity, suggests faster diffusion consistent with both experimental and simulation values.

Atomistic molecular dynamics simulations were carried out to investigate the molecular mechanisms of vertical surface alignment of liquid crystals. We study the insertion of nCB (4-Cyano-4'-n-biphenyl) molecules with n = 0,…,6 into a bent-core liquid crystal monolayer that was recently found to provide good vertical alignment for liquid crystals. The results suggest a complex-free energy landscape for the liquid crystal within the layer. The preferred insertion direction of the nCB molecules (core or tail first) varies with n, which can be explained by entropic considerations. The role of the dipole moments was found to be negligible. As vertical alignment is the leading form of present day liquid crystal displays (LCD), these results will help guide improvement of the LCD technology, as well as lend insight into the more general problem of insertion of biological and other molecules into lipid and surfactant layers.