Internal structure visualization and lithographic use of periodic toroidal holes in liquid crystals

Abstract

The formation of a large-area ordered structure by organic molecular soft building blocks is one of the most exciting interdisciplinary research areas in current materials science and nanotechnology. So far, several distinct organic building blocks--including colloids, block copolymers and surfactants--have been examined as potential materials for the creation of lithographic templates. Here, we report that perfect ordered arrays of toric focal conic domains (TFCDs) covering large areas can be formed by semi-fluorinated smectic liquid crystals. Combined with controlled geometry, that is, a microchannel, our smectic liquid-crystal system exhibits a high density of TFCDs that are arranged with remarkably high regularity. Direct visualization of the internal structure of the TFCDs clearly verified that the smectic layers were aligned normal to the side walls and parallel to the top surface, and merge with the circular profile on the bottom wall surface. Moreover, we demonstrate a new concept: smectic liquid-crystal lithography. Grown in microchannels from a mixture of liquid-crystal molecules and fluorescent particles, TFCDs of the smectic liquid crystals acted as a template, trapping particles in an ordered array. Our findings pose new theoretical challenges and potentially enable lithographic applications based on smectic liquid-crystalline materials.

Organization of the polarization splay modulated smectic liquid crystal phase by topographic confinement

“…The boundary areas between B7 phase and isotropic phase show relatively large birefringence. (17,18). Such a motif has been found in smectic films with competing planar and homeotropic orientations on opposite surfaces and leads to linear periodic arrays of toroidal focal conic domains in channels with surfaces fostering planar alignment.…”

“…As for many smectics appearing upon cooling directly from the isotropic phase via a first order transition, i.e., having no intervening nematic phase, the B7s are not easily aligned into macroscopically oriented domains of any sort with the anisotropic surface treatment methods such as optical-or mechanical-rubbed polymer surfaces or obliquely deposited silicon monoxide (SiOx) (7-11) that are typically useful for aligning LCs. Topographic patterning has been demonstrated to align LCs (12-14) and has recently emerged as an effective alignment technique for both nematic and smectic LCs, and in particular for layered LC phases growing directly from the isotropic (15)(16)(17)(18).In this paper we report the successful use of topographical confinement to control the spatial organization of the B7 smectic phase, employing linear micron-scale channels of rectangular cross-section etched into the surface of silicon wafers. Smectic layer orientation normal to the channel walls and bottom is enforced by a preference for random planar alignment of the molecular long axes on the channel surfaces.…”

Imprintable membranes from incomplete chiral coalescence

“…However, being a consequence of random coalescence events, the spatial location of such defects is impossible to control. It is therefore desirable to develop a robust on-demand method for imprinting defects into colloidal membranes with arbitrary spatial precision, similar to recent work with thermotropic liquid crystals [32][33][34] . We demonstrate that membrane self-coalescence can be induced with optical forces (Fig.…”

Direct mapping of local director field of nematic liquid crystals at the nanoscale

“…Although we have become adept at deducing textures indirectly through optical microscopies (1)(2)(3)(4)(5), probing the molecular-scale organization requires either a glassy material or rapid cooling of samples, providing metastable states that can be directly visualized through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) (6)(7)(8). Although these techniques are effective to study a variety of more complex LC phases, including smectic LCs (6,7,9), cholesteric and blue phases (10), and biological LC polymers (11,12), nonglassy, low molecular weight nematic LCs (NLCs) reorient during fast freezing. Polymer nematics can be quenched into metastable states but organization of static configurations through surface alignment is difficult.…”