Chinese Journal of Liquid Crystals and Displays, Volume. 39, Issue 5, 569(2024)
Photoalignment guided order evolution of liquid crystals
Fig. 1. Different liquid crystal phases. Schemes of director distributions and typical microscopic textures of(a)nematic phase,(b)cholesteric phase and(c)smectic phase liquid crystals[30].
Fig. 3. Topological defects in nematic liquid crystals.(a)Schematics of point defects with different topological charges in two-dimensional liquid crystal systems[33];(b)Schematics of disclination lines formed by different combinations in three-dimensional liquid crystal systems[34];(c)Schematics of splay-bend,twist and mixed wall defects[35].
Fig. 4. Topological defects in smectic A phase.(a)Schematic of FCD with characteristic defect pairs as confocal ellipses and hyperbolas,and its polarized microscope image[31];(b)Schematic of TFCD with characteristic defect pairs as circular defects in confocal and linear defects over the center of a circle,and its polarized microscope image[38-39];(c)Schematic of SFCD with characteristic defect pairs as the two asymptotes of the characteristic hyperbolic defects parallel and perpendicular to the substrate,and its polarized microscope image[40];(d)Schematic of FCDs closely alternating to form the Zigzag-FCD and its polarized microscope image[41];(e)Schematic of PFCD with characteristic defects as the two parabolic defect pairs in confocal andits polarized microscope image[42-43];(f)Schematic of OS with one-dimensional lattice periodic distribution of characteristic defects in thin layer liquid crystal system and its polarized microscope image[44].
Fig. 5. Basic types of FCDs[36].(a)Schematic of FCD-I with negative Gaussian curvature;(b)Schematic of FCD-Ⅱ with positive Gaussian curvature;(c)Schematic of FCD-Ⅲ with both positive and negative positive Gaussian curvature.
Fig. 6. Evolutionsof topological defects across the N-S phase transition.(a)Schematics of ±1 point defects and their evolutions during the N-S phase transition;(b)Orientation patterns with periodic distribution of+1 and -1 singularities enabled by photoalignment technology and the evolutions of ±1 point defects during the N-S phase transition under slow cooling;(c)Evolutions of disclination lines during the N-S phase transition under rapid cooling,and the formation of wall defects in the N phase;(d)Relationship between system energy F and temperature T during the N-S phase transition,topological analysis of three different N textures and the coexistence of point defects and wall defects[5].
Fig. 7. Controlled evolutions of topological defects across the N-S phase transitions.(a)Structural evolutions of disclination lines and wall defects when the initial azimuthal angles of the radial orientational alignment lattices are 0°,30°,60°,and 90°,respectively[11];(b)Periodic and quasiperiodic topological defects with Ci(i=2~6)symmetries guided by alignment lattices with different symmetries,and their topological analysis. The lattice types and symmetries are rectangular lattice(C2),diamond lattice(C2),triangular lattice(C3),square lattice(C4),quasiperiodic lattice(C5),and hexagonal lattice(C6),respectively[12].
Fig. 8. Controlled generation of TFCDs,SFCDs and d-TFCDs.(a)Polarized microscopy images and SEM images of TFCDs with one-dimensional periodicity under microchannel confinement[51];(b)Realization of TFCDs array with controllable unit domain size enabled by photoalignment technology[8];(c)Formation of SCFDs array guided by periodic alternating ± 45° orientation pattern and its structural dependence on orientational angle[6];(d)Generations of d-TFCDs array supported by complex alignment designs[7].
Fig. 9. Microlens functions of TFCDs and d-TFCDs.(a)Schematic of imaging for TFCDs microlens array[52];(b)Continuous tuning of focal length of polymer stabilized TFCDs microlens array enabled by external electric fields[8];(c)Imaging characterization of FCDs microlens array with continuous variation in unit size[54];(d)Four-dimensional imaging characterization of d-TFCDs microlens arrays[7].
Fig. 10. Other advanced applications of TFCDs.(a)Optical diffraction characteristics of SFCDs array[6];(b)Diffraction characterization of periodic and quasiperiodic TFCDs array with Ci(i=2~6)symmetries[31];(c)Fluorescent silicaparticles captured by TFCDs array to achieve particles array assembly[51];(d)Generation of vortex optical arrays with topological charge s=2 using TFCDs array[55].
Fig. 11. Controllable generation of OSs.(a)Three-dimensional schematic of OSs[58];(b)Programmable arbitrary patterned OSs enabled by photoalignment technology[29];(c)Switching state and structural rotation of the OSs under the external electric fields[29];(d)Realization of reversible rotation of chiral OSs under light stimulations[9].
Fig. 12. Functional applications of OSs.(a)Diffraction characterization of patterned OSs gratings[65];(b)Characterization of chiral OSs gratings with reversible rotation stimulated by light[9];(c)Self-assembly of gold nanoparticle arrays using OSs and characterization of surface enhanced Raman scattering effect[66-67];(d)Superhydrophobic surface achieved by OSs[68];(e)Cell culture enabled by OSs[69].
Fig. 13. Investigation of transformation from FCDs to OSs.(a)Schematic of one-dimensional periodic OSs and two-dimensional periodic FCDs,and the structural transformations observed when film thickness varies[59];(b)Evolution of OSs to FCDs under different film thicknesses based on photoalignment technology[10];(c)Polarization micrograph of liquid crystal system in critical phase transition state with gradient changes in film thickness,phase diagram of critical temperature T and film thickness derivative 1/h[71];(d)Transformation from FCDs to OSs achieved by applying external electric fields[72].
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Daoxing LUO, Jinbing WU, Zhenghao GUO, Wei HU. Photoalignment guided order evolution of liquid crystals[J]. Chinese Journal of Liquid Crystals and Displays, 2024, 39(5): 569
Category: Research Articles
Received: Feb. 2, 2024
Accepted: --
Published Online: Jul. 8, 2024
The Author Email: Wei HU (huwei@nju.edu.cn)