Strength of Memory-Induced Anchoring of 5CB on Bare Untreated ITO

Electrodynamic-contact-line-lithography with nematic liquid crystals for template-less E-writing of mesopatterns on soft surfaces

We report the development of a single-step, template-less and fast pathway, namely, Electrodynamic-Contact-Line-Lithography (ECLL), to write micro to nanopatterns on the surface of a soft polymer film. As a model system, a layer of nematic liquid crystals (NLC), resting on a polymer thin film, was sandwiched between a pair of electrodes emulating the electrowetting on a dielectric (EWOD) setup. Upon the application of electric field, the Maxwell stresses thus generated at the NLC-polymer interface due to the high dielectric contrast stimulated an unprecedented fingering instability at the advancing NLC-polymer-air contact line. In the process, the advancing electrospreading front of NLC left the footprint of an array of micro to nanoscale wells on the polymer surface with a long-range ordering thus unveiling a pathway for maskless patterning of a soft elastic film. Unlike the conventional electric field induced lithography (EFL), the meso-scale morphology was found to follow the short wavelength-scales as the periodicity of the patterns (λ_c) varied linearly with the thickness of the film (h), (λ_c∝h). The high dielectric contrast at the NLC-polymer interface and the local fluctuation of the NLC directors ensured a time scale much faster than the same observed for the polymer-air systems.

Periodic dynamics, localization metastability, and elastic interaction of colloidal particles with confining surfaces and helicoidal structure of cholesteric liquid crystals

Nematic and cholesteric liquid crystals are three-dimensional fluids that possess long-range orientational ordering and can support both topological defects and chiral superstructures. Implications of this ordering remain unexplored even for simple dynamic processes such as the ones found in so-called "fall experiments," or motion of a spherical inclusion under the effects of gravity. Here we show that elastic and surface anchoring interactions prompt periodic dynamics of colloidal microparticles in confined cholesterics when gravity acts along the helical axis. We explore elastic interactions between colloidal microparticles and confining surfaces as well as with an aligned ground-state helical structure of cholesterics for different sizes of spheres relative to the cholesteric pitch, demonstrating unexpected departures from Stokes-like behavior at very low Reynolds numbers. We characterize metastable localization of microspheres under the effects of elastic and surface anchoring periodic potential landscapes seen by moving spheres, demonstrating the important roles played by anchoring memory, confinement, and topological defect transformation. These experimental findings are consistent with the results of numerical modeling performed through minimizing the total free energy due to colloidal inclusions at different locations along the helical axis and with respect to the confining substrates. A potential application emerging from this work is colloidal sorting based on particle shapes and sizes.

Microscopic investigation of the memory effect found in micropatterned nematic liquid crystal cells

Isotropic untreated indium-tin-oxide layers can cause memory alignment of nematic liquid crystals. We have demonstrated an experimental method to characterize this effect by using a micropatterned surface. We tried to imprint a high tilt on an indium-tin-oxide substrate surface. We also investigated microscopic switching behavior of a memory-induced nematic liquid crystal cell by means of a vertical field effect.