Sharp Morphological Transitions from Nanoscale Mixed-Anchoring Patterns in Confined Nematic Liquid Crystals

Abstract

Liquid crystals are known to be particularly sensitive to orientational cues provided at surfaces or interfaces. In this work, we explore theoretically, computationally, and experimentally the behavior of liquid crystals on isolated nanoscale patterns with controlled anchoring characteristics at small length scales. The orientation of the liquid crystal is controlled through the use of chemically patterned polymer brushes that are tethered to a surface. This system can be engineered with remarkable precision, and the central question addressed here is whether a characteristic length scale exists at which information encoded on a surface is no longer registered by a liquid crystal. To do so, we adopt a tensorial description of the free energy of the hybrid liquid-crystal-surface system, and we investigate its morphology in a systematic manner. For long and narrow surface stripes, it is found that the liquid crystal follows the instructions provided by the pattern down to 100 nm widths. This is accomplished through the creation of line defects that travel along the sides of the stripes. We show that a "sharp" morphological transition occurs from a uniform undistorted alignment to a dual uniform/splay-bend morphology. The theoretical and numerical predictions advanced here are confirmed by experimental observations. Our combined analysis suggests that nanoscale patterns can be used to manipulate the orientation of liquid crystals at a fraction of the energetic cost that is involved in traditional liquid crystal-based devices. The insights presented in this work have the potential to provide a new fabrication platform to assemble low power bistable devices, which could be reconfigured upon application of small external fields.

Molecular Orientation Depth Profiles in Organic Glasses Using Polarized Resonant Soft X-ray Reflectivity

“…Vertical stratification in crystallinity and/or crystal or molecular orientation has also been reported in single component organic semiconductors. , Ion-containing systems, such as ionic liquids, polymer electrolytes, and doped organic semiconductors also exhibit vertical stratification. In liquid crystals, orientational cues from substrates and superstrates can lead to complex orientation depth profiles . In biological membranes, vertical stratification of various functional groups is not just an accidental material property, it is a key to their function .…”

Writing Theory and Modeling Papers for Langmuir: The Good, the Bad, and the Ugly

“…6 Recent work by Armas-Peŕez et al is an excellent example of using validation between multiple levels and modeling and experimental data. 7 There is a temptation in writing a modeling manuscript to focus on comparing results with other previous calculations. This kind of comparison should, of course, not be discouraged, but it is important to remember that comparing simulation A to simulation B cannot provide any information about whether these simulations say something meaningful about the real world.…”

“…Hardy and Bock’s recent work on the identification of solvents for dispersing carbon nanotubes is one good example of the careful validation of atomistic modeling with extensive experimental data . Recent work by Armas-Pérez et al is an excellent example of using validation between multiple levels and modeling and experimental data . There is a temptation in writing a modeling manuscript to focus on comparing results with other previous calculations.…”

Selective Liquid Crystal Driving Mode Achieved by Controlling the Pretilt Angle via a Nanopatterned Organic/Inorganic Hybrid Thin Film

“…[ 1 ] Recently, for advanced LC applications, a number of methods to align LC molecules have been researched, such as ion‐beam alignment, [ 2–5 ] photoalignment, [ 7 ] oblique evaporation, [ 8 ] and embossing. [ 9–11 ] Among these methods, embossing is the most powerful and simple for aligning LC molecules because it has the advantages of high throughput and low cost. It can be used to fabricate uniform 3D nanostructures over a large area and is compatible with mass production.…”

“…Intensive research is being conducted on uniform LC alignment using organic/inorganic materials as alignment layers via various alignment techniques. [1][2][3][4][5][6][7][8][9][10][11] Rubbing of the polyimide (PI) layer with a roller is the conventional alignment method for generating micro-sized grooves on the PI surface and unidirectionally anchoring the LC molecules. [1] Recently, for advanced LC applications, a number of methods to align LC molecules have been researched, such as ion-beam alignment, [2][3][4][5] photoalignment, [7] oblique evaporation, [8] and embossing.…”