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Omori E, Zola R, de Souza RT. Stable disclination lines in nematic liquid crystals confined in thin films with periodic-planar surfaces: A Monte Carlo study. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.117538] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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2
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Basu R. Graphene as an alignment agent, an electrode, and a source of surface chirality in a smectic-A liquid crystal. Phys Rev E 2021; 103:022710. [PMID: 33735989 DOI: 10.1103/physreve.103.022710] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 02/10/2021] [Indexed: 11/07/2022]
Abstract
A liquid crystal (LC) cell was fabricated by putting together a monolayer graphene-coated glass substrate on one side, and a rubbed planar-aligning polyimide layer on an indium tin oxide (ITO) coated glass substrate on the other side. The monolayer graphene film served as the planar-alignment agent as well as the transparent electrode on one side of the cell. The cell was filled with an achiral LC alkoxyphenylbenzoate (9OO4). The presence of the graphene film on one substrate resulted in an induced chiral signature in the otherwise achiral LC 9OO4. The induced chirality was probed utilizing the electroclinic effect (a polar tilt of the LC director perpendicular to, and linear in, an applied electric field) in the smectic-A phase. The electroclinic effect showed significant pretransitional behavior on approaching the smectic-A to smectic-C transition temperature from above. The electroclinic effect revealed a low-frequency relaxation process indicating that the chirality was induced on the LC molecules at the graphene interface and did not propagate into the bulk. A soft shear mode can break the symmetry of the hexagonal lattice of graphene on a substrate and, consequently, graphene possesses strain chirality. The noncovalent π-π interaction between the LC and the strained graphene induces molecular conformational deracemization in the LC at the graphene interface, and the LC exhibits surface-induced chirality.
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Affiliation(s)
- Rajratan Basu
- Department of Physics, Soft Matter and Nanomaterials Laboratory, The United States Naval Academy, Annapolis, Maryland 21402, USA
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3
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Wetting of Nematic Liquid Crystals on Crenellated Substrates: A Frank–Oseen Approach. CRYSTALS 2019. [DOI: 10.3390/cryst9080430] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We revisit the wetting of nematic liquid crystals in contact with crenellated substrates, studied previously using the Landau–de Gennes formalism. However, due to computational limitations, the characteristic length scales of the substrate relief considered in that study limited to less than 100 nematic correlation lengths. The current work uses an extended Frank–Oseen formalism, which includes not only the free-energy contribution due to the elastic deformations but also the surface tension contributions and, if disclinations or other orientational field singularities are present, their core contributions. Within this framework, which was successfully applied to the anchoring transitions of a nematic liquid crystal in contact with structured substrates, we extended the study to much larger length scales including the macroscopic scale. In particular, we analyzed the interfacial states and the transitions between them at the nematic–isotropic coexistence.
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4
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Nemitz IR, Gryn I, Boudet N, Lemieux RP, Goldmann M, Zappone B, Petschek RG, Rosenblatt C, Lacaze E. Observations of a streak texture in the hybrid-aligned smectic-C phase. SOFT MATTER 2018; 14:460-469. [PMID: 29214250 DOI: 10.1039/c7sm02129a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A novel structure was observed below the smectic-A-smectic-C phase transition in a very thin open cell having an air interface above and enforced planar anchoring at the substrate below. The structure appears as periodic dark and light streaks running perpendicular to the oily streaks, which are present in the smectic-A phase [D. Coursault et al., Soft Matter, 2016, 12, 678]. These new streaks, which we call "soapy streaks", form by extending from one oily streak to the next in discrete steps, eliminating optical evidence at visible wavelengths of the oily streaks. At lower temperatures the streaks can undulate and exhibit a sawtooth-like structure; such a structure is chiral in two dimensions. A possible scenario for the origin of these streaks is presented.
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Affiliation(s)
- I R Nemitz
- Dept. of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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5
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Rojas-Gómez ÓA, Romero-Enrique JM, Silvestre NM, Telo da Gama MM. Pattern-induced anchoring transitions in nematic liquid crystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:064002. [PMID: 28002041 DOI: 10.1088/1361-648x/29/6/064002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In this paper we revisit the problem of a nematic liquid crystal in contact with patterned substrates. The substrate is modelled as a periodic array of parallel infinite grooves of well-defined cross-section sculpted on a chemically homogeneous substrate which favours local homeotropic anchoring of the nematic. We consider three cases: a sawtooth, a crenellated and a sinusoidal substrate. We analyse this problem within the modified Frank-Oseen formalism. We argue that, for substrate periodicities much larger than the extrapolation length, the existence of different nematic textures with distinct far-field orientations, as well as the anchoring transitions between them, are associated with the presence of topological defects either on or close to the substrate. For the sawtooth and sinusoidal cases, we observe a homeotropic to planar anchoring transition as the substrate roughness increases. On the other hand, a homeotropic to oblique anchoring transition is observed for crenellated substrates. In this case, the anchoring phase diagram shows a complex dependence on the substrate roughness and substrate anchoring strength.
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Affiliation(s)
- Óscar A Rojas-Gómez
- Departamento de Física Atómica, Molecular y Nuclear, Area de Física Teórica, Universidad de Sevilla, Apartado de Correos 1065, 41080 Sevilla, Spain
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6
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Nemitz IR, Lacaze E, Rosenblatt C. Electroclinic effect in a chiral paranematic liquid-crystal layer above the bulk nematic-to-isotropic transition temperature. Phys Rev E 2016; 93:022701. [PMID: 26986382 DOI: 10.1103/physreve.93.022701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Indexed: 06/05/2023]
Abstract
Electroclinic measurements are reported for two chiral liquid crystals above their bulk chiral isotropic-nematic phase transition temperatures. It is found that an applied electric field E induces a rotation θ [∝Ε] of the director in the very thin paranematic layers that are induced by the cell's two planar-aligning substrates. The magnitude of the electroclinic coefficient dθ/dE close to the transition temperature is comparable to that of a bulk chiral nematic, as well as to that of a parasmectic region above a bulk isotropic-to-chiral smectic-A phase. However, dθ/dE in the paranematic layer varies much more slowly with temperature than in the parasmectic phase, and its relaxation time is slower by more than three orders of magnitude than that of the bulk chiral nematic electroclinic effect.
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Affiliation(s)
- Ian R Nemitz
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
- CNRS UMR 7588, Université Pierre et Marie Curie, Institut des NanoSciences de Paris (INSP), 4 place Jussieu, 75005 Paris, France
- UPMC Université Paris VI, UMR 7588, Institut des NanoSciences de Paris (INSP), 4 place Jussieu, 75005 Paris, France
| | - Emmanuelle Lacaze
- CNRS UMR 7588, Université Pierre et Marie Curie, Institut des NanoSciences de Paris (INSP), 4 place Jussieu, 75005 Paris, France
- UPMC Université Paris VI, UMR 7588, Institut des NanoSciences de Paris (INSP), 4 place Jussieu, 75005 Paris, France
| | - Charles Rosenblatt
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
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7
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DeBenedictis A, Atherton TJ, Anquetil-Deck C, Cleaver DJ, Emerson DB, Wolak M, Adler JH. Competition of lattice and basis for alignment of nematic liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:042501. [PMID: 26565259 DOI: 10.1103/physreve.92.042501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Indexed: 06/05/2023]
Abstract
Due to elastic anisotropy, two-dimensional patterning of substrates can promote weak azimuthal alignment of adjacent nematic liquid crystals. Here we consider how such alignment can be achieved using a periodic square lattice of circular or elliptical motifs. In particular, we examine ways in which the lattice and motif can combine to favor differing orientations. Using Monte Carlo simulation and continuum elasticity we find, for circular motifs, that the coverage fraction controls both the polar anchoring angle and a transition in the azimuthal orientation. If the circles are generalized to ellipses, arbitrary control of the effective easy axis and effective anchoring potential becomes achievable by appropriate tuning of the ellipse motif relative to the periodic lattice patterning. This has possible applications in both monostable and bistable liquid crystal device contexts.
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Affiliation(s)
- Andrew DeBenedictis
- Department of Physics and Astronomy, Tufts University, 574 Boston Avenue, Medford, Massachusetts 02155, USA
| | - Timothy J Atherton
- Department of Physics and Astronomy, Tufts University, 574 Boston Avenue, Medford, Massachusetts 02155, USA
| | - Candy Anquetil-Deck
- Materials and Engineering Research Institute, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB, United Kingdom
| | - Douglas J Cleaver
- Materials and Engineering Research Institute, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB, United Kingdom
| | - David B Emerson
- Department of Mathematics, Tufts University, 503 Boston Avenue, Medford, Massachusetts 02155, USA
| | - Mathew Wolak
- Department of Mathematics, Tufts University, 503 Boston Avenue, Medford, Massachusetts 02155, USA
| | - James H Adler
- Department of Mathematics, Tufts University, 503 Boston Avenue, Medford, Massachusetts 02155, USA
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8
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Bai Y, Abbasi R, Wang C, Abbott NL. Liquid Crystals Anchored on Mixed Monolayers of Chiral versus Achiral Molecules: Continuous Change in Orientation as a Function of Enantiomeric Excess. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201402770] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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9
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Bai Y, Abbasi R, Wang C, Abbott NL. Liquid crystals anchored on mixed monolayers of chiral versus achiral molecules: continuous change in orientation as a function of enantiomeric excess. Angew Chem Int Ed Engl 2014; 53:8079-83. [PMID: 24841757 PMCID: PMC4241358 DOI: 10.1002/anie.201402770] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Indexed: 11/10/2022]
Abstract
The orientations of liquid crystals (LCs) anchored on monolayers formed from mixtures of chiral versus achiral molecules were compared. Changes in the enantiomeric excess of mixed monolayers of chiral dipeptides gave rise to continuous changes in the orientations of nematic LCs, allowing arbitrary tuning of the azimuthal orientations of LCs over a range of ≈100°. In contrast, the same LCs exhibited discontinuous changes in orientation on surfaces presenting mixtures of achiral molecules. These striking differences in the anchoring of LCs on surfaces presenting chiral versus achiral molecules provide insights into the molecular origins of ordering transitions of LCs, and provide new principles based on chiral monolayers for the rational design of surfaces that permit continuous tuning of the orientations of LCs.
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Affiliation(s)
- Yiqun Bai
- Department of Chemical and Biological Engineering University of Wisconsin-Madison 1415 Engineering Drive, Madison WI 53705, USA
| | - Reza Abbasi
- Department of Chemical and Biological Engineering University of Wisconsin-Madison 1415 Engineering Drive, Madison WI 53705, USA
| | - Chenxuan Wang
- Department of Chemical and Biological Engineering University of Wisconsin-Madison 1415 Engineering Drive, Madison WI 53705, USA
| | - Nicholas L. Abbott
- Department of Chemical and Biological Engineering University of Wisconsin-Madison 1415 Engineering Drive, Madison WI 53705, USA
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10
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Meyer C, Luckhurst GR, Dozov I. Flexoelectrically driven electroclinic effect in the twist-bend nematic phase of achiral molecules with bent shapes. PHYSICAL REVIEW LETTERS 2013; 111:067801. [PMID: 23971614 DOI: 10.1103/physrevlett.111.067801] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Indexed: 06/02/2023]
Abstract
We extend the twist-bend nematic (N(TB)) model to describe the electro-optics of this novel phase. We predict an electroclinic effect (ECE) subject to a dc electric field E applied perpendicular to the helix axis or wave vector q, with rotation of the N(TB) optic axis around E. This linear effect, with its flexoelectric origin, is a close analog to the electro-optic effects observed for chiral liquid crystals. However, in nematics composed of achiral molecules having a bent shape, it is the electro-optic signature of the N(TB) phase. We test our model experimentally in the low-temperature nematic phase of the odd liquid crystal dimer, CB7CB, with its molecules having, on average, a bent shape. The ECE measurements confirm the previously proposed twist-bend nematic structure of this phase, with its broken chiral symmetry, extremely short (<10 nm) doubly degenerate pitch and ultrafast, submicrosecond response times.
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Affiliation(s)
- C Meyer
- Physique des Systèmes Complexes, Université de Picardie Jules Verne, 80039 Amiens, France
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11
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Rojas-Gómez OA, Romero-Enrique JM. Generalized Berreman's model of the elastic surface free energy of a nematic liquid crystal on a sawtoothed substrate. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:041706. [PMID: 23214602 DOI: 10.1103/physreve.86.041706] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 10/05/2012] [Indexed: 06/01/2023]
Abstract
In this paper we present a generalization of Berreman's model for the elastic contribution to the surface free-energy density of a nematic liquid crystal in presence of a sawtooth substrate which favors homeotropic anchoring as a function of the wave number of the surface structure q, the tilt angle α, and the surface anchoring strength w. In addition to the previously reported nonanalytic contribution proportional to -q ln q, due to the nucleation of disclination lines at the wedge bottoms and apexes of the substrate, the next-to-leading contribution is proportional to q for a given substrate roughness, in agreement with Berreman's predictions. We characterize this term, finding that it has two contributions: the deviations of the nematic director field with respect to a reference field corresponding to the isolated disclination lines and their associated core free energies. Comparison with the results obtained from the Landau-de Gennes model shows that our model is quite accurate in the limit wL>1, when strong anchoring conditions are effectively achieved.
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Affiliation(s)
- O A Rojas-Gómez
- Departamento de Física Atómica, Molecular y Nuclear, Area de Física Teórica Universidad de Sevilla, Apartado de Correos 1065, 41080 Sevilla, Spain
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12
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Ohzono T, Fukuda JI, Suzuki K, Yamaguchi T. ±1/2 wedge disclinations stabilized by a sinusoidal boundary in a thin hybrid nematic liquid-crystal film. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:030701. [PMID: 23030857 DOI: 10.1103/physreve.86.030701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Indexed: 06/01/2023]
Abstract
As an interesting example of how geometry affects the formation of defects, we study the defect structures of a hybrid nematic liquid-crystal film in a wedge-shaped cell made up of sinusoidal microwrinkles and an elastomer sheet. When the cell thickness is larger than a threshold value h(c), +1/2 and -1/2 disclinations are simultaneously stabilized along concave grooves and convex crests, respectively. A simple theoretical analysis gives a good estimate of h(c). The disclinations also show alternating optical rotations resulting from the curved boundary and liquid-crystal elastic anisotropy.
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Affiliation(s)
- Takuya Ohzono
- Nanosystem Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan.
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13
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Basu R, Nemitz IR, Song Q, Lemieux RP, Rosenblatt C. Surface topography and rotational symmetry breaking. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:011711. [PMID: 23005441 DOI: 10.1103/physreve.86.011711] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Indexed: 06/01/2023]
Abstract
The surface electroclinic effect, which is a rotation of the molecular director in the substrate plane proportional to an electric field E applied normal to the substrate, requires both a chiral environment and C(2) (or lower) rotational symmetry about E. The two symmetries typically are created in tandem by manipulating the surface topography, a process that conflates their effects. Here we use a pair of rubbed polymer-coated substrates in a twist geometry to obtain our main result, viz., that the strengths of two symmetries, in this case the rub-induced breaking of C(∞) rotational symmetry and chiral symmetry, can be separated and quantified. Experimentally we observe that the strength of the reduced rotational symmetry arising from the rub-induced scratches, which is proportional to the electroclinic response, scales linearly with the induced topographical rms roughness and increases with increasing rubbing strength of the polymer. Our results also suggest that the azimuthal anchoring strength coefficient is relatively insensitive to the strength of the rubbing.
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Affiliation(s)
- Rajratan Basu
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
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14
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Ohzono T, Fukuda JI. Zigzag line defects and manipulation of colloids in a nematic liquid crystal in microwrinkle grooves. Nat Commun 2012; 3:701. [PMID: 22426222 PMCID: PMC3293426 DOI: 10.1038/ncomms1709] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 01/25/2012] [Indexed: 11/21/2022] Open
Abstract
Spatially confined liquid crystals exhibit non-uniform alignment, often accompanied by self-organised topological defects of non-trivial shape in response to imposed boundary conditions and geometry. Here we show that a nematic liquid crystal, when confined in a sinusoidal microwrinkle groove, exhibits a new periodic arrangement of twist deformations and a zigzag line defect. This periodic ordering results from the inherent liquid crystal elastic anisotropy and the antagonistic boundary conditions at the flat liquid crystal-air and the curved liquid crystal-groove interfaces. The periodic structure can be tuned by controlling the groove geometry and the molecular chirality, which demonstrates the importance of boundary conditions and introduced asymmetry for the engineering of topological defects. Moreover, the kinks in the zigzag defects can trap small particles, which may afford a new method for manipulation of colloids. Our system, which uses easily fabricated microwrinkle grooves, provides a new microfabrication method based on the arrangement of controllable defects.
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Affiliation(s)
- Takuya Ohzono
- Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Japan.
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15
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Bai Y, Abbott NL. Enantiomeric interactions between liquid crystals and organized monolayers of tyrosine-containing dipeptides. J Am Chem Soc 2012; 134:548-58. [PMID: 22091988 PMCID: PMC3257416 DOI: 10.1021/ja2089475] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have examined the orientational ordering of nematic liquid crystals (LCs) supported on organized monolayers of dipeptides with the goal of understanding how peptide-based interfaces encode intermolecular interactions that are amplified into supramolecular ordering. By characterizing the orientations of nematic LCs (4-cyano-4'-pentylbiphenyl and TL205 (a mixture of mesogens containing cyclohexane-fluorinated biphenyls and fluorinated terphenyls)) on monolayers of l-cysteine-l-tyrosine, l-cysteine-l-phenylalanine, or l-cysteine-l-phosphotyrosine formed on crystallographically textured films of gold, we conclude that patterns of hydrogen bonds generated by the organized monolayers of dipeptides are transduced via macroscopic orientational ordering of the LCs. This conclusion is supported by the observation that the ordering exhibited by the achiral LCs is specific to the enantiomers used to form the dipeptide-based monolayers. The dominant role of the -OH group of tyrosine in dictating the patterns of hydrogen bonds that orient the LCs was also evidenced by the effects of phosphorylation of the tyrosine on the ordering of the LCs. Overall, these results reveal that crystallographic texturing of gold films can direct the formation of monolayers of dipeptides with long-range order, thus unmasking the influence of hydrogen bonding, chirality, and phosphorylation on the macroscopic orientational ordering of LCs supported on these surfaces. These results suggest new approaches based on supramolecular assembly for reporting the chemical functionality and stereochemistry of synthetic and biological peptide-based molecules displayed at surfaces.
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Affiliation(s)
- Yiqun Bai
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison WI 53705, United States
| | - Nicholas L. Abbott
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison WI 53705, United States
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16
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Basu R, Pendery JS, Petschek RG, Lemieux RP, Rosenblatt C. Macroscopic torsional strain and induced molecular conformational deracemization. PHYSICAL REVIEW LETTERS 2011; 107:237804. [PMID: 22182127 DOI: 10.1103/physrevlett.107.237804] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Indexed: 05/31/2023]
Abstract
A macroscopic helical twist is imposed on an achiral nematic liquid crystal by controlling the azimuthal alignment directions at the two substrates. On application of an electric field the director rotates in the substrate plane. This electroclinic effect, which requires the presence of chirality, is strongest at the two substrates and increases with increasing imposed twist distortion. We present a simple model involving a trade-off among bulk elastic energy, surface anchoring energy, and deracemization entropy that suggests the large equilibrium director rotation induces a deracemization of chiral conformations in the molecules-effectively "top-down" chiral induction-quantitatively consistent with experiment.
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Affiliation(s)
- Rajratan Basu
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106, USA
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17
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Malone SM, Schwartz DK. Macroscopic liquid crystal response to isolated DNA helices. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:11767-11772. [PMID: 21894894 DOI: 10.1021/la202640a] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Nematic liquid crystals (LC) were exposed to isolated DNA molecules extended on a surface that imparted a negligible influence on the LC orientation. Although single-stranded DNA aligned the LC in the extension direction, double-stranded DNA (dsDNA) caused alignment at an oblique angle, providing a characteristic response to the chiral dsDNA helix that was readily observed optically. The intrinsic amplification due to LC orientational correlations enabled a macroscopic visible response to a single molecule of extended dsDNA.
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Affiliation(s)
- Stephanie M Malone
- Department of Chemical & Biological Engineering, University of Colorado at Boulder, Boulder, Colorado 80309, USA
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18
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Yi Y, Maclennan JE, Clark NA. Cooperative liquid-crystal alignment generated by overlaid topography. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:051708. [PMID: 21728557 DOI: 10.1103/physreve.83.051708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Revised: 04/18/2011] [Indexed: 05/31/2023]
Abstract
Nematic and smectic liquid crystals were introduced into μm-scale gaps between plates coated with polymer films nanoimprinted with parallel arrays of rectangular channels. Overlaying the channels on the two plates close enough at a slight angle produces a mosaic of alternating planar and homeotropic alignments and hybrid alignment, showing that complex liquid-crystal orientation patterns can be achieved by combining two simple topographic patterns. These alignment patterns are attributed to spatial variation of surface roughness and 3D topographic structure created by a sufficient proximity of the two patterns.
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Affiliation(s)
- Youngwoo Yi
- Department of Physics and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
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19
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Basu R, Petschek RG, Rosenblatt C. Nematic electroclinic effect in a carbon-nanotube-doped achiral liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:041707. [PMID: 21599186 DOI: 10.1103/physreve.83.041707] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Indexed: 05/30/2023]
Abstract
A small quantity of carbon nanotubes (CNTs) dispersed in an achiral liquid crystal (LC) matrix transmits chirality a short distance into the LC, and the LC+CNT mixture is found to exhibit a bulklike electroclinic effect in the nematic phase. The magnitude of the effect increases rapidly on cooling, showing significant pretransitional behavior on approaching the nematic-smectic-A transition temperature (T(NA)) from above. The variation of the electroclinic coefficient is negligible over the frequency range 100 Hz to 100 kHz in the in the nematic phase well above T(NA) and in the smectic-A phase, whereas the electroclinic coefficient falls off significantly with increasing frequency just above T(NA).
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Affiliation(s)
- Rajratan Basu
- Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106-7079, USA
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20
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Chiral symmetry breaking by spatial confinement in tactoidal droplets of lyotropic chromonic liquid crystals. Proc Natl Acad Sci U S A 2011; 108:5163-8. [PMID: 21402929 DOI: 10.1073/pnas.1100087108] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In many colloidal systems, an orientationally ordered nematic (N) phase emerges from the isotropic (I) melt in the form of spindle-like birefringent tactoids. In cases studied so far, the tactoids always reveal a mirror-symmetric nonchiral structure, sometimes even when the building units are chiral. We report on chiral symmetry breaking in the nematic tactoids formed in molecularly nonchiral polymer-crowded aqueous solutions of low-molecular weight disodium cromoglycate. The parity is broken by twisted packing of self-assembled molecular aggregates within the tactoids as manifested by the observed optical activity. Fluorescent confocal microscopy reveals that the chiral N tactoids are located at the boundaries of cells. We explain the chirality induction as a replacement of energetically costly splay packing of the aggregates within the curved bipolar tactoidal shape with twisted packing. The effect represents a simple pathway of macroscopic chirality induction in an organic system with no molecular chirality, as the only requirements are orientational order and curved shape of confinement.
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