Orientation of a Helical Nanofilament (B4) Liquid‐Crystal Phase: Topographic Control of Confinement, Shear Flow, and Temperature Gradients

Yoon, Dong Ki; Yi, Yu Hyeon; Shen, Yongqiang; Körblová, Eva; Walba, David M.; Smalyukh, Ivan I.; Clark, Noel A.

doi:10.1002/adma.201004482

Cited by 43 publications

(45 citation statements)

References 23 publications

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“…Achieving such control has proven to be challenging, with conventional LC aligning methods such as optical-or mechanical-rubbed polymer surfaces (23,24) for aligning bent-core LCs failing completely. However, some recent works have reported the successful achievement for this issue (25) using the combination of topographical confinement thermal gradients and external shear forces (26), the directionally rubbed cells with rod-like guiding materials (15,27), and the chemically modified surfaces (28). These investigations for macroscopic organization led us to explore HNF growth under conditions of confinement in pores, and we were surprised to find conditions under individual perfect HNFs grow in each pore in an AAO array ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Multistep hierarchical self-assembly of chiral nanopore arrays

Kim

Lee

Shin

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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A series of simple hierarchical self-assembly steps achieve selforganization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements.aluminum oxide | liquid crystal | chirality | nanoconfinement | bent-core C ontrolled nanoscale self-assembly (SA) is one of the most important subjects in chemistry, physics, and materials science and technology. Currently, soft matter systems such as block copolymers (BCPs), biomaterials, colloids, supramolecules, and liquid crystals (LCs) are widely explored as building blocks for self-assembly because of their diverse themes of nanostructural organization (1-3). Of particular interest in this effort are nanostructures that are hierarchically SA over a broad range of length scales, because these both advance basic SA science and promise practical uses in a broad array of materials applications (4). Here we present a composite nanomaterial system based on hierarchically template-assisted self-assembly (TSA) wherein, in absence of any predisposed pattern, a series of hierarchical steps spontaneously produces, over square centimeter areas, nanopore arrays with large internal surface areas of chiral crystal interfaces.This system is based on the marriage of two robust SA scenarios: (i) the formation of films of Al 2 O 3 populated with arrays of nanometer-scale pores by the anodic oxidation of aluminum, combined with (ii) the helical crystalline nanofilament formation of the B4 phase of bent-core mesogenic molecules (4). Anodic aluminum oxide (AAO) films are one of the most widely used nanoporous media, spontaneously forming uniform cylindrical pores, 5-450 nm in diameter and many microns long, with a high areal density (∼10 9 pores/cm 2 ) and low polydispersity in size (Materials and Methods) (5-7). Such AAO pores have been used as templates for the organization of soft matter nanostructures, such as BCP lamellae, cylinders, and other structures (8-10). In these and other AAO-based self-assembled nanosystems, fabrication extends down to the mesoscopic-length scales, the interfaces produced being fluid or amorphous solid structures. Approaches for generating intrapore interfaces with the controlled atom-scale organization required for many applications, for example, the electrodeposition of crystals (11,12), generally plug the pores. We sought to explore systems that combined robust crystalline ordering with a definitive crystal morphology that would enable the fabrication by SA of clear channels with crystal interfaces running through the length of the AAO pores. The helical nanofilaments reported here represent a striking realization of this goal, promising a host of chemical and photonic applications, for example in nonlinear optics (13)(14)(15).

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Section: Resultsmentioning

confidence: 99%

Multistep hierarchical self-assembly of chiral nanopore arrays

Kim

Lee

Shin

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…These structures have exotic physicochemical properties, which originate from spontaneously broken symmetries even though the LC material itself does not have any chiral centre such as a chiral carbon. 3,10,11 Owing to the symmetry breaking of the sublayers of the bent-core molecule, deformations of the local saddle-splay layer occur simultaneously in the flat layered structures. [7][8][9] Among the layered structures of bent-core LC phases, the B4 (helical nanofilament, HNF) phase is the most complex structure, [5][6][7] in which layers are helically twisted with specific dimensions of B35 nm in diameter and B110 nm in half-pitch.…”

Section: Introductionmentioning

confidence: 99%

Physico-chemical confinement of helical nanofilaments

et al. 2015

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Helical nanofilaments (HNFs) have attracted much interest because of their unique optical properties, but there have been many hurdles to overcome in using them for the practical applications due to their structural complexity. Here we demonstrate that the molecular configuration and layer conformation of a modulated HNF (HNFs(mod)) can be studied using a physicochemical confinement system. The layer directions affected by the chemical affinity between the mesogen and surface were drastically controlled in surface-modified nanochannels. Furthermore, an in situ experiment using grazing-incidence X-ray diffraction (GIXD) was carried out to investigate in detail the structural evolution through thermal transitions. The results demonstrate that the HNF(mod) structure can be perfectly controlled for functional HNF device applications, and a combined system with chemical and physical confinement effects will be helpful to better understand the fundamentals of soft matter.

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“…Self-organization in soft matter systems, such as colloids23, block copolymers45 and liquid crystals67, is widely used for designing materials with emergent properties and for templating structures with new functionalities. Recently, fabrication of periodic patterns focuses on the integration of top-down (lithographic) and bottom-up methods because structures prepared solely by self-organization often lack sufficient long-range order, which is crucial for practical use.…”

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confidence: 99%

Large-scale self-organization of reconfigurable topological defect networks in nematic liquid crystals

et al. 2016

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Topological defects in nematic liquid crystals are ubiquitous. The defects are important in understanding the fundamental properties of the systems, as well as in practical applications, such as colloidal self-assembly, optical vortex generation and templates for molecular self-assembly. Usually, spatially and temporally stable defects require geometrical frustration imposed by surfaces; otherwise, the system relaxes because of the high cost of the elastic energy. So far, multiple defects are kept in bulk nematic liquid crystals by top-down lithographic techniques. In this work, we stabilize a large number of umbilical defects by doping with an ionic impurity. This method does not require pre-patterned surfaces. We demonstrate that molecular reorientation controlled by an AC voltage induces periodic density modulation of ions accumulated at an electrically insulating polymer interface, resulting in self-organization of a two-dimensional square array of umbilical defects that is reconfigurable and tunable.

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Orientation of a Helical Nanofilament (B4) Liquid‐Crystal Phase: Topographic Control of Confinement, Shear Flow, and Temperature Gradients

Cited by 43 publications

References 23 publications

Multistep hierarchical self-assembly of chiral nanopore arrays

Multistep hierarchical self-assembly of chiral nanopore arrays

Physico-chemical confinement of helical nanofilaments

Large-scale self-organization of reconfigurable topological defect networks in nematic liquid crystals

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