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

Journal Article · Mon Sep 25 00:00:00 EDT 2017 · Langmuir

DOI:https://doi.org/10.1021/acs.langmuir.7b02522· OSTI ID:1417669

Armas-Perez, Julio C.  ^[1]; Li, Xiao  ^[2]; Martinez-Gonzalez, Jos A. ^[2]; Smith, Coleman ^[2]; Hernandez-Ortiz, J. P.  ^[3]; Nealey, Paul F.  ^[4]; de Pablo, Juan J.  ^[4]

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1. Univ. of Chicago, Chicago, IL (United States); Univ. de Guanajuato, Guanajuato (Mexico)
2. Univ. of Chicago, Chicago, IL (United States)
3. Univ. Nacional de Colombia, Medellin (Colombia)
4. Univ. of Chicago, Chicago, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)

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.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Wisconsin, Madison (United States); Univ. of Chicago, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-06CH11357; SC0004025
• OSTI ID: 1417669
• Alternate ID(s): OSTI ID: 1603438
• Journal Information: Langmuir, Vol. 33, Issue 43; ISSN 0743-7463
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY