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Dolganov PV, Zhilin VM. Electric-field-induced transition from helical to planar smectic structures without helix unwinding. Phys Rev E 2013; 87:062505. [PMID: 23848703 DOI: 10.1103/physreve.87.062505] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2013] [Revised: 03/12/2013] [Indexed: 11/07/2022]
Abstract
Previously electric-field-induced transitions from helical to planar structures in bulk liquid crystals were considered to take place with unwinding of helix. We show that the transition to the planar structure in polar smectic with frustrating interlayer interaction can occur without unwinding but through the formation of a periodic modulated structure with successive left-hand and right-hand sense of rotation in every half period. With field the amplitude of the left-right rotation decreases and a planar structure is formed. This mechanism of transition can take place in the short-pitch SmC(α)(*) phase formed as a result of frustrating interaction.
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Affiliation(s)
- P V Dolganov
- Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
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2
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McCoy BK, Pan L, Liu ZQ, Wang ST, Wang S, Goodby JW, Huang CC. Evolution of a rare sequence of surface transitions with temperature and film thickness. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:031712. [PMID: 20365756 DOI: 10.1103/physreve.81.031712] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Indexed: 05/29/2023]
Abstract
In free-standing smectic films, layers near the surfaces of the film often contain molecules tilted away from the layer normal, while in the bulk of the film the magnitude of the tilt decays exponentially with distance from the surface. We have identified the detailed molecular tilt orientations in the surface layers of films for one antiferroelectric liquid crystal compound. A series of five surface structures exists with different nonplanar tilt arrangements for each structure. The molecular orientations in the surface layers evolve with temperature. The polarization of the film also evolves with temperature, corresponding to the tilt arrangements. Using ellipsometric data, we reconstruct the changes in the magnitude and azimuthal direction of the tilt as functions of temperature. We have also studied films of several different thicknesses. We present a phase diagram for the five surface structures showing the dependence on temperature and film thickness.
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Affiliation(s)
- B K McCoy
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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McCoy BK, Liu ZQ, Wang ST, Pan L, Wang S, Goodby JW, Huang CC. Nonplanar tilts in very thin smectic films of one liquid-crystal compound. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:061702. [PMID: 19658511 DOI: 10.1103/physreve.79.061702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Indexed: 05/28/2023]
Abstract
Surface effects cause tilted molecular arrangements in smectic layers near the surface of a free-standing liquid-crystal film in which the bulk of the film is in the smectic- A phase. One recent work has shown that the tilt directions in adjacent surface layers may be nonplanar. In this paper we study films with thicknesses of two to six smectic layers. Surface effects dominate in these very thin films. We show that the molecular tilts are nonplanar even in these very thin films.
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Affiliation(s)
- B K McCoy
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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4
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Pan L, Wang S, Hsu CS, Huang CC. Surface-induced ordering effect in one antiferroelectric liquid crystal compound. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:031704. [PMID: 19391959 DOI: 10.1103/physreve.79.031704] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2008] [Indexed: 05/27/2023]
Abstract
Null transmission ellipsometer was employed to study the surface-induced tilt transition of an antiferroelectric liquid crystal compound in the bulk smectic- A (SmA) temperature range. The data of the surface tilt transition can be fitted with an extended mean-field model. These results indicate the transition is near a mean-field tricritical point. The surface layers' tilt directions are found to be in different planes several degrees above the bulk SmA-SmC_{alpha};{ *} transition.
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Affiliation(s)
- Lidong Pan
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Wang ST, Han XF, Liu ZQ, McCoy BK, Huang CC. Optical studies on the surface-induced tilted layers in freestanding films of two no-layer-shrinkage liquid crystal compounds. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 74:031707. [PMID: 17025654 DOI: 10.1103/physreve.74.031707] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2006] [Indexed: 05/12/2023]
Abstract
Null transmission ellipsometry has been employed to study the molecular arrangements in freestanding films of two no-layer-shrinkage liquid crystal homologous compounds above the bulk smectic A-smectic C* (Sm C*) transition temperature. An unusual nonplanar-parallel or nonplanar-antiparallel-parallel transition has been observed in both compounds under a proper electric field. With the addition of one CH2 group, while the SmC* phase is more stable thermally, the magnitude of the critical field needed to induce a parallel-antiparallel transition decreases dramatically.
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Affiliation(s)
- S T Wang
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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McCoy BK, Liu ZQ, Wang ST, Panov VP, Vij JK, Goodby JW, Huang CC. Surface-induced multiple reentrant transitions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:041704. [PMID: 16711824 DOI: 10.1103/physreve.73.041704] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2005] [Indexed: 05/09/2023]
Abstract
We have studied tilted surface layers in the bulk SmA temperature window of one liquid crystal using null transmission ellipsometry. Five distinct nonplanar surface structures were observed. We present analyses of the tilt and azimuthal profiles of the structures and examine the transitions between the structures. The transitions are identified as a double reentrant synclinic-anticlinic-synclinic-anticlinic transition. Meanwhile, the transitions also display reentrant ferroelectric-antiferroelectric-ferroelectric behavior.
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Affiliation(s)
- B K McCoy
- School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
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7
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Conradi M, Cepic M, Copic M, Musevic I. Test of clock model in ellipsometric study of thin and thick free-standing films of an antiferroelectric liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 72:051711. [PMID: 16383624 DOI: 10.1103/physreve.72.051711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2005] [Indexed: 05/05/2023]
Abstract
The temperature dependences of the ellipsometric parameters in a weak dc external field are studied in thin and thick free-standing films of MHPOBC. The results for thin films consisting of two, three, and four layers are analyzed within the discrete phenomenological model. We find very good quantitative agreement between the theory and experiment, which indicates an odd-even effect. We find that the XY structures are stable for an odd number of layers, whereas planar, Ising-like structures are stable for an even number of layers. The experiments on thick (several tens of layers) films show a combination of bulklike and free-surface behavior. This is most pronounced at high temperatures, where the interior of the film is not tilted, whereas the layers at the air interfaces show qualitatively similar temperature dependance of the ellipsometric parameters as in the four-layer film.
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Affiliation(s)
- M Conradi
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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Wang ST, Han XF, Liu ZQ, Cady A, Radcliffe MD, Huang CC. Unusual behavior of the surface-induced tilted layers in free-standing films of a non-layer-shrinkage liquid crystal compound. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:060702. [PMID: 14754172 DOI: 10.1103/physreve.68.060702] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2003] [Indexed: 05/24/2023]
Abstract
Null-transmission ellipsometry has been conducted to study the molecular arrangements in free-standing films of one chiral compound above the bulk smectic-A-smectic-C* transition temperature. Upon cooling under a proper electric field, a nonplanar-anticlinic-synclinic or a nonplanar-synclinic transition has been observed. The nonplanar structure continuously evolves into the anticlinic or synclinic structures. Increasing electric field can induce a rare transition from a synclinic to an anticlinic structure.
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Affiliation(s)
- S T Wang
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Sigarev AA, Vij JK, Lewis RA, Hird M, Goodby JW. Molecular orientation and the infrared dichroism of a chiral smectic liquid crystal in a homogeneously aligned cell at different temperature and bias fields. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:031707. [PMID: 14524788 DOI: 10.1103/physreve.68.031707] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2003] [Indexed: 05/24/2023]
Abstract
The molecular orientation and the dichroic behavior of the vibrational bands of a homogeneously aligned helical cell containing chiral smectic liquid crystal (R)-(-)-1-methylheptyl 4-(4(')-dodecyloxybiphenyl-4-ylcarbonyloxy)-3-fluorobenzoate are studied at various temperatures as a function of the bias field. These temperatures correspond to the various phase states of the sample at zero field. For those bands that exhibit significant dichroism, the field dependencies of the dichroic parameters (the dichroic ratio and the polarization angle of maximum absorbance) are found to be dependent on temperature, phase state, and helical unwinding. For the SmA* and SmC(*)(alpha) phases, the phenyl band dichroic ratio and the corresponding orientational order parameter are found to be almost independent of the bias field. The temperature dependence of the orientational order for zero field is discussed by taking into account the structures of the phases and the molecular tilt angles. The field dependencies of the phenyl band dichroic parameters for the SmC(*)(A) and SmC(*)(gamma) phases yield results about the distribution of directors in the layers of their unit cells and the state of helical unwinding. The azimuthal orientational distribution function of the carbonyl transition moments with respect to the long molecular axis has been determined. It is found that the degrees of the polar and quadrupolar biasing increase with decrease in temperature and the azimuthal biasing angle for the chiral carbonyl group increases significantly with a reduction in temperature.
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Affiliation(s)
- A A Sigarev
- Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland
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Han XF, Wang ST, Cady A, Radcliffe MD, Huang CC. Double reentrance of surface arrangements in freestanding liquid crystal films. PHYSICAL REVIEW LETTERS 2003; 91:045501. [PMID: 12906671 DOI: 10.1103/physrevlett.91.045501] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2003] [Indexed: 05/24/2023]
Abstract
The molecular arrangement of tilted surface layers on freestanding films above the bulk smectic-A-smectic-C(*) transition has been studied by null transmission ellipsometry. In the presence of an applied in-plane electric field, a synclinic-anticlinic-synclinic-anticlinic double reentrance has been observed. Furthermore, we have characterized a novel transition from the synclinic arrangement to a structure in which the interior layers tilt in the same orientation and the outermost surface layers tilt oppositely with the interior layers.
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Affiliation(s)
- X F Han
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
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