Chiral Liquid Crystal Lenses Confined in Microchannels

Abstract

It is known that the liquid crystalline smectic-A phase has geometric defects, called focal conic domains, which can be used as gradient-index microlenses. Cholesteric (chiral nematic) phases also have topological defects with a central symmetry and a singularity at their center. We explore a weakly chiral system in which both types of defects can be present in the same material at different temperatures, and with this strategy we create lenses whose focal length is tunable with temperature. We measure the focal length of the tunable lenses, and we investigate the behavior of the defects near the phase transition. We identify the experimental conditions that make the simultaneous presence of the smectic focal conic domains and the circular cholesteric domains possible, such as the concentration of chiral dopant and the rate of heating and cooling. The transformation of focal conic domains into circular cholesteric domains is a new example of memory at the phase transition between smectic-A and nematic liquid crystals.

Electrically Tunable Microlens Array Enabled by Polymer‐Stabilized Smectic Hierarchical Architectures

“…This can be explained by a memory effect of director orientation during the N‐SmA phase transition, which directs the deformation of smectic layers. [ 25,31 ] Thus through properly designing the radial alignment lattice, 3D layered structures of TFCDs including the domain size and lattice symmetry are freely manipulated. Photoalignment is a noncontact technique that avoids mechanical damage and residual debris and is suitable for large‐area and high‐quality hierarchical architecting.…”

Photo‐Actuated Chiral Smectic Superstructures

“…The OSs also function as gratings with multi‐field sensitivities, such as temperature, light wavelength, and incident polarization. [ 29 ] The strategy of combining chirality and hierarchy can be extended to various smectic LC configurations in addition to OSs, [ 30 ] and even to other layered architectures assembled by surfactants and colloidal particles. [ 31 ]…”

Sublimation of isolated toric focal conic domains on micro-patterned surfaces

“…Examples of such soft materials include block copolymers, 6,7 stacked membranes, [8][9][10] and various liquid crystals (LCs). [11][12][13][14][15][16] A LC is a state of matter with intermediate properties between liquids and crystals. Of particular interest is the smectic phase of LCs, characterized by layered molecular ordering, in which these molecular layers maintain equidistance.…”