More Like this

1. Azimuthal Anchoring Strength in Photopatterned Alignment of a Nematic

   https://doi.org/10.3390/cryst11060675  

   Padmini, H. Nilanthi; Rajabi, Mojtaba; Shiyanovskii, Sergij V.; Lavrentovich, Oleg D. (June 2021, Crystals)

   null (Ed.)

   Spatially-varying director fields have become an important part of research and development in liquid crystals. Characterization of the anchoring strength associated with a spatially-varying director is difficult, since the methods developed for a uniform alignment are seldom applicable. Here we characterize the strength of azimuthal surface anchoring produced by the photoalignment technique based on plasmonic metamsaks. The measurements used photopatterned arrays of topological point defects of strength +1 and −1 in thin layers of a nematic liquid crystal. The integer-strength defects split into pairs of half-integer defects with lower elastic energy. The separation distance between the split pair is limited by the azimuthal surface anchoring, which allows one to determine the strength of the latter. The strength of the azimuthal anchoring is proportional to the UV exposure time during the photoalignment of the azobenzene layer. 

   more » « less
2. Tunable three-dimensional architecture of nematic disclination lines

   https://doi.org/10.1073/pnas.2300833120  

   Modin, Alvin; Ash, Biswarup; Ishimoto, Kelsey; Leheny, Robert L; Serra, Francesca; Aharoni, Hillel (July 2023, Proceedings of the National Academy of Sciences)

   Disclination lines play a key role in many physical processes, from the fracture of materials to the formation of the early universe. Achieving versatile control over disclinations is key to developing novel electro-optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, we introduce a theoretical framework to tailor three-dimensional disclination architecture in nematic liquid crystals experimentally. We produce quantitative predictions for the connectivity and shape of disclination lines found in nematics confined between two thinly spaced glass substrates with strong patterned planar anchoring. By drawing an analogy between nematic liquid crystals and magnetostatics, we find that i) disclination lines connect defects with the same topological charge on opposite surfaces and ii) disclination lines are attracted to regions of the highest twist. Using polarized light to pattern the in-plane alignment of liquid crystal molecules, we test these predictions experimentally and identify critical parameters that tune the disclination lines’ curvature. We verify our predictions with computer simulations and find nondimensional parameters enabling us to match experiments and simulations at different length scales. Our work provides a powerful method to understand and practically control defect lines in nematic liquid crystals. 

   more » « less
3. Repulsion–attraction switching of nematic colloids formed by liquid crystal dispersions of polygonal prisms

   https://doi.org/10.1039/c7sm01186e  

   Senyuk, B.; Liu, Q.; Nystrom, P. D.; Smalyukh, I. I. (January 2017, Soft Matter)

   Self-assembly of colloidal particles due to elastic interactions in nematic liquid crystals promises tunable composite materials and can be guided by exploiting surface functionalization, geometric shape and topology, though these means of controlling self-assembly remain limited. Here, we realize low-symmetry achiral and chiral elastic colloids in the nematic liquid crystals using colloidal polygonal concave and convex prisms. We show that the controlled pinning of disclinations at the prism edges alters the symmetry of director distortions around the prisms and their orientation with respect to the far-field director. The controlled localization of the disclinations at the prism's edges significantly influences the anisotropy of the diffusion properties of prisms dispersed in liquid crystals and allows one to modify their self-assembly. We show that elastic interactions between polygonal prisms can be switched between repulsive and attractive just by controlled re-pinning the disclinations at different edges using laser tweezers. Our findings demonstrate that elastic interactions between colloidal particles dispersed in nematic liquid crystals are sensitive to the topologically equivalent but geometrically rich controlled configurations of the particle-induced defects. 

   more » « less
4. Directing and reconfiguring colloidal assembly by disclination networks in nematic liquid crystal as templates

   https://doi.org/10.1016/j.giant.2023.100228  

   Guo, Yubing; Jiang, Miao; Afghah, Sajedeh; Peng, Chenghui; Selinger, Robin LB; Lavrentovich, Oleg D; Wei, Qi-Huo (March 2024, Giant)

   Exotic structures with interesting physical and chemical properties can be achieved by self-organizing engineered building blocks. The central aim for self-assembly is to precisely control the position and orientation of individual building blocks. In this work, we use topological defects (disclinations) in nematic liquid crystals as templates to direct the self-assembly of colloidal particles into designable 3D structures. By photopatterning preprogrammed molecular orientations at two confining surfaces, we created pre-designable disclination networks and characterized their interactions with spherical colloidal particles. We find that colloidal particles are attracted to different disclinations depending on the orientation of the point defect (elastic dipole) around the colloids. We demonstrate that the positions, network structures, and orientation of the elastic dipoles of the colloidal chains can be pre-designed and reconfigured with remote illumination of polarized light. 

   more » « less
5. Surface alignment of ferroelectric nematic liquid crystals

   https://doi.org/10.1039/d1sm00734c  

   Caimi, Federico; Nava, Giovanni; Barboza, Raouf; Clark, Noel A.; Korblova, Eva; Walba, David M.; Bellini, Tommaso; Lucchetti, Liana (September 2021, Soft Matter)

   The success of nematic liquid crystals in displays and optical applications is due to the combination of their optical uniaxiality, fluidity, elasticity, responsiveness to electric fields and controllable coupling of the molecular orientation at the interface with solid surfaces. The discovery of a polar nematic phase opens new possibilities for liquid crystal-based applications, but also requires a new study of how this phase couples with surfaces. Here we explore the surface alignment of the ferroelectric nematic phase by testing different rubbed and unrubbed substrates that differ in coupling strength and anchoring orientation and find a variety of behaviors – in terms of nematic orientation, topological defects and electric field response – that are specific to the ferroelectric nematic phase and can be understood as a consequence of the polar symmetry breaking. In particular, we show that by using rubbed polymer surfaces it is easy to produce cells with a planar polar preferential alignment and that cell electrostatics ( e.g. grounding the electrodes) has a remarkable effect on the overall homogeneity of the ferroelectric ordering. 

   more » « less