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Abstract
We present analytical calculations of the energies and eigenfunctions of all normal modes of excitation of charge +1 two-dimensional splay (bend) disclinations confined to an annular region with inner radius R1 and outer radius R2 and with perpendicular (tangential) boundary conditions on the region’s inner and outer perimeters. Defects such as these appear in islands in smectic-C films and can in principle be created in bolaamphiphilic nematic films. Under perpendicular boundary conditions on the two surfaces and when the ratio β=Ks/Kb of the splay to bend 2D Frank constants is less than one, the splay configuration is stable for all values μ=R2/R1. When β>1, the splay configuration is stable only for μ less than a critical value μc(β), becoming unstable to a “spiral” mixed splay-bend configuration for μ>μc. The same behavior occurs in trapped bend defects with tangential boundary conditions but with Ks and Kb interchanged. By calculating free energies, we verify that the transition from a splay or bend configuration to a mixed one is continuous. We discuss the differences between our calculations that yield expressions for experimentally observable excitation energies and other calculations that produce the same critical points and spiral configurations as ours but not the same excitation energies. We also calculate measurable correlation functions and associated decay times of angular fluctuations.
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Camley BA, Brown FLH. Motion of objects embedded in lipid bilayer membranes: Advection and effective viscosity. J Chem Phys 2019; 151:124104. [PMID: 31575184 DOI: 10.1063/1.5121418] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
An interfacial regularized Stokeslet scheme is presented to predict the motion of solid bodies (e.g., proteins or gel-phase domains) embedded within flowing lipid bilayer membranes. The approach provides a numerical route to calculate velocities and angular velocities in complex flow fields that are not amenable to simple Faxén-like approximations. Additionally, when applied to shearing motions, the calculations yield predictions for the effective surface viscosity of dilute rigid-body-laden membranes. In the case of cylindrical proteins, effective viscosity calculations are compared to two prior analytical predictions from the literature. Effective viscosity predictions for a dilute suspension of rod-shaped objects in the membrane are also presented.
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Affiliation(s)
- Brian A Camley
- Departments of Physics & Astronomy and Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Frank L H Brown
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
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Radzihovsky SP, Cranfill C, Nguyen Z, Park CS, Maclennan JE, Glaser MA, Clark NA. Two-dimensional island emulsions in ultrathin, freely-suspended smectic liquid crystal films. SOFT MATTER 2017; 13:6314-6321. [PMID: 28849846 DOI: 10.1039/c7sm01584d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report a novel type of two-dimensional colloidal emulsion, in which arrays of disc-shaped liquid crystal domains are created in ultrathin, freely-suspended, fluid smectic C liquid crystal films. After a film has been drawn across an aperture, an island emulsion is produced by repeatedly compressing and expanding the film while maintaining vigorous shear and extensional air flow across its area. Once formed, these emulsions restructure over a period of a few minutes to a stable state that then changes only slowly, over the course of several days. This stability enables study of the sedimentation of the emulsion under in-plane gravitation produced by tilting the film, during which the original island emulsion segregates into regions with different kinds of emulsions distinguished by the size, density, and degree of order of the islands. We observe a rich array of phenomena that includes the formation of chains of islands organized into two-dimensional smectics in the dilute phase, and island deformation and coalescence in the condensed phase.
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Affiliation(s)
- Sarah P Radzihovsky
- Soft Materials Research Center and Department of Physics, University of Colorado Boulder, Boulder, CO 80309, USA.
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Qi Z, Ferguson K, Sechrest Y, Munsat T, Park CS, Glaser MA, Maclennan JE, Clark NA, Kuriabova T, Powers TR. Active microrheology of smectic membranes. Phys Rev E 2017; 95:022702. [PMID: 28297876 DOI: 10.1103/physreve.95.022702] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Indexed: 11/07/2022]
Abstract
Thin fluid membranes embedded in a bulk fluid of different viscosity are of fundamental interest as experimental realizations of quasi-two-dimensional fluids and as models of biological membranes. We have probed the hydrodynamics of thin fluid membranes by active microrheology using small tracer particles to observe the highly anisotropic flow fields generated around a rigid oscillating post inserted into a freely suspended smectic liquid crystal film that is surrounded by air. In general, at distances more than a few Saffman lengths from the meniscus around the post, the measured velocities are larger than the flow computed by modeling a moving disklike inclusion of finite extent by superposing Levine-MacKintosh response functions for pointlike inclusions in a viscous membrane. The observed discrepancy is attributed to additional coupling of the film with the air below the film that is displaced directly by the shaft of the moving post.
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Affiliation(s)
- Zhiyuan Qi
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.,Soft Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Kyle Ferguson
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.,Soft Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Yancey Sechrest
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Tobin Munsat
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Cheol Soo Park
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.,Soft Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Matthew A Glaser
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.,Soft Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Joseph E Maclennan
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.,Soft Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Noel A Clark
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.,Soft Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Tatiana Kuriabova
- Department of Physics, California Polytechnic State University, San Luis Obispo, California 93407, USA
| | - Thomas R Powers
- School of Engineering and Department of Physics, Brown University, Providence, Rhode Island 02912, USA
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