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Ngo VT, Nguyen PT, Diep HT. Statistical Physics Approach to Liquid Crystals: Dynamics of Mobile Potts Model Leading to Smectic Phase, Phase Transition by Wang-Landau Method. ENTROPY (BASEL, SWITZERLAND) 2020; 22:E1232. [PMID: 33286999 PMCID: PMC7711670 DOI: 10.3390/e22111232] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 10/18/2020] [Accepted: 10/26/2020] [Indexed: 11/16/2022]
Abstract
We study the nature of the smectic-isotropic phase transition using a mobile 6-state Potts model. Each Potts state represents a molecular orientation. We show that with the choice of an appropriate microscopic Hamiltonian describing the interaction between individual molecules modeled by a mobile 6-state Potts spins, we observe the smectic phase dynamically formed when we cool the molecules from the isotropic phase to low temperatures (T). In order to elucidate the order of the transition and the low-T properties, we use the high-performance Wang-Landau flat energy-histogram technique. We show that the smectic phase goes to the liquid (isotropic) phase by melting/evaporating layer by layer starting from the film surface with increasing T. At a higher T, the whole remaining layers become orientationally disordered. The melting of each layer is characterized by a peak of the specific heat. Such a succession of partial transitions cannot be seen by the Metropolis algorithm. The successive layer meltings/evaporations at low T are found to have a first-order character by examining the energy histogram. These results are in agreement with experiments performed on some smectic liquid crystals.
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Affiliation(s)
- V. Thanh Ngo
- Center for Informatics and Computing, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi 10000, Vietnam;
- Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi 10000, Vietnam;
| | - Phuong-Thuy Nguyen
- Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi 10000, Vietnam;
- Institute of Physics, Vietnam Academy of Science and Technology, 10 Dao Tan, Hanoi 10000, Vietnam
| | - Hung T. Diep
- Laboratoire de Physique Théorique et Modélisation, CY Cergy Paris Université (Formerly, University of Cergy-Pontoise), CNRS, UMR 8089, 2 Avenue Adolphe Chauvin, 95302 Cergy-Pontoise, France
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Zaluzhnyy IA, Kurta RP, Sulyanova EA, Gorobtsov OY, Shabalin AG, Zozulya AV, Menushenkov AP, Sprung M, Krówczyński A, Górecka E, Ostrovskii BI, Vartanyants IA. Structural studies of the bond-orientational order and hexatic-smectic transition in liquid crystals of various compositions. SOFT MATTER 2017; 13:3240-3252. [PMID: 28402369 DOI: 10.1039/c7sm00343a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We report on the X-ray studies of freely suspended hexatic films of three different liquid crystal compounds. By applying angular X-ray cross-correlation analysis (XCCA) to the measured diffraction patterns the parameters of the bond-orientational (BO) order in the hexatic phase were directly determined. The temperature evolution of the BO order parameters was analyzed on the basis of the multicritical scaling theory (MCST). Our results confirmed the validity of the MCST in the whole temperature range of the existence of the hexatic phase for all three compounds. The temperature dependence of the BO order parameters in the vicinity of the hexatic-smectic transition was fitted by a conventional power law with a critical exponent β ≈ 0.1 of extremely small value. We found that the temperature dependence of higher order harmonics of the BO order scales as the powers of the first harmonic, with an exponent equal to the harmonic number. This indicates a nonlinear coupling of the BO order parameters of different order. We demonstrate that compounds of various compositions, possessing different phase sequences at low temperatures, display the same thermodynamic behavior in the hexatic phase and in the vicinity of the smectic-hexatic phase transition.
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Affiliation(s)
- I A Zaluzhnyy
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany. and National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe shosse 31, 115409 Moscow, Russia
| | - R P Kurta
- European XFEL GmbH, Holzkoppel 4, D-22869 Schenefeld, Germany
| | - E A Sulyanova
- FSRC "Crystallography and Photonics", Russian Academy of Sciences, Leninskii prospect 59, 119333 Moscow, Russia.
| | - O Yu Gorobtsov
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
| | - A G Shabalin
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
| | - A V Zozulya
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
| | - A P Menushenkov
- National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe shosse 31, 115409 Moscow, Russia
| | - M Sprung
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.
| | - A Krówczyński
- Department of Chemistry, University of Warsaw, Zwirki I Wigury 101, 02-089, Warsaw, Poland
| | - E Górecka
- Department of Chemistry, University of Warsaw, Zwirki I Wigury 101, 02-089, Warsaw, Poland
| | - B I Ostrovskii
- FSRC "Crystallography and Photonics", Russian Academy of Sciences, Leninskii prospect 59, 119333 Moscow, Russia. and Landau Institute for Theoretical Physics, Russian Academy of Sciences, prospect akademika Semenova 1-A, 142432 Chernogolovka, Russia
| | - I A Vartanyants
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany. and National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe shosse 31, 115409 Moscow, Russia
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Pereira MSS, de Oliveira IN, Lyra ML. Crossover from tricritical to critical end point behavior in free-standing smectic films. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 84:061706. [PMID: 22304108 DOI: 10.1103/physreve.84.061706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Indexed: 05/31/2023]
Abstract
We study the smectic to nematic (SmA-N) phase transition taking place at the center of a free-standing film that exhibits enhanced surface order due to the anchoring promoted by a surrounding gas. The usual McMillan mean-field approach predicts that the SmA-N transition in bulk samples can be continuous or discontinuous (first or second order) depending on the molecular geometry, with a tricritical point separating these two regimes. Here we show that the additional orientational order imposed by the surface anchoring stabilizes the surface-induced smectic and nematic phases, leading to the breakdown of the tricritical point and to the emergence of a critical end point. We report the full phase diagram, which depicts four distinct structures as the film thickness is reduced.
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Affiliation(s)
- Maria S S Pereira
- Instituto de Física, Universidade Federal de Alagoas, 57072-970 Maceió, Alagoas, Brazil
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Bohley C, Stannarius R. Inclusions in free standing smectic liquid crystal films. SOFT MATTER 2008; 4:683-702. [PMID: 32907171 DOI: 10.1039/b715124a] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Colloidal inclusions in thin free standing liquid crystal films are ideal model systems for 2D anisotropic dispersions. Different types of self-organization in chain and lattice structures have been observed. The orientational elasticity of the anisotropic matrix and capillary forces are the dominating interaction mechanisms between solid or liquid inclusions, the director field, and dislocations of the films. We give an overview of the progress in this field, focussing on different inclusion types and their interactions in thermotropic smectic films.
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Affiliation(s)
- Christian Bohley
- Otto-von-Guericke Universität Magdeburg, Institute of Experimental Physics, Magdeburg, 39106, Germany.
| | - Ralf Stannarius
- Otto-von-Guericke Universität Magdeburg, Institute of Experimental Physics, Magdeburg, 39106, Germany.
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Alba-Simionesco C, Coasne B, Dosseh G, Dudziak G, Gubbins KE, Radhakrishnan R, Sliwinska-Bartkowiak M. Effects of confinement on freezing and melting. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2006; 18:R15-R68. [PMID: 21697556 DOI: 10.1088/0953-8984/18/6/r01] [Citation(s) in RCA: 337] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We present a review of experimental, theoretical, and molecular simulation studies of confinement effects on freezing and melting. We consider both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials). The most commonly used molecular simulation, theoretical and experimental methods are first presented. We also provide a brief description of the most widely used porous materials. The current state of knowledge on the effects of confinement on structure and freezing temperature, and the appearance of new surface-driven and confinement-driven phases are then discussed. We also address how confinement affects the glass transition.
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Affiliation(s)
- C Alba-Simionesco
- Laboratoire de Chimie Physique, CNRS-UMR 8000, Bâtiment 349, Université de Paris-Sud, F-91405 Orsay, France
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Brannigan G, Lin LCL, Brown FLH. Implicit solvent simulation models for biomembranes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 35:104-24. [PMID: 16187129 DOI: 10.1007/s00249-005-0013-y] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2005] [Revised: 08/03/2005] [Accepted: 08/12/2005] [Indexed: 11/25/2022]
Abstract
Fully atomic simulation strategies are infeasible for the study of many processes of interest to membrane biology, biophysics and biochemistry. We review various coarse-grained simulation methodologies with special emphasis on methods and models that do not require the explicit simulation of water. Examples from our own research demonstrate that such models have potential for simulating a variety of biologically relevant phenomena at the membrane surface.
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Affiliation(s)
- Grace Brannigan
- Department of Physics and Astronomy, University of California, Santa Barbara, CA 93106-9530, USA
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Chao CY, Hsieh WJ, Hsu MT, Ho JT, Lin IJB. A new hexatic phase observed in biomembrane‐like films. LIQUID CRYSTALS TODAY 2005. [DOI: 10.1080/14645180500358835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Chao CY, Hsu MT, Hsieh WJ, Ho JT, Lin IJB. New hexatic liquid phase observed in lyotropic thin films. PHYSICAL REVIEW LETTERS 2004; 93:247801. [PMID: 15697859 DOI: 10.1103/physrevlett.93.247801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2004] [Indexed: 05/24/2023]
Abstract
An intermediate surface hexatic phase between the liquid and the crystalline phases has been found for the first time in a lyotropic lamellar liquid-crystal system. This phase is highly unusual in that it has long-range sixfold bond-orientational order but liquidlike nearest-neighbor positional correlations, and could represent a significant departure from our current understanding of defect-mediated melting in two dimensions.
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Affiliation(s)
- Chih-Yu Chao
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan, Republic of China.
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Harroun TA, Raghunathan VA, Pencer J, Nieh MP, Katsaras J. Finite-size effects in biomimetic smectic films. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 70:062902. [PMID: 15697418 DOI: 10.1103/physreve.70.062902] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Indexed: 05/24/2023]
Abstract
Thin stacks of lipid multibilayers supported on rigid silicon and mica substrates are found to exhibit finite-size effects. Using neutron diffraction we find that the repeat spacing (d) of stacks containing up to a few tens of bilayers depends on their thickness (D), with d increasing with decreasing D. Differences in d are larger in the low-temperature Lbeta' phase consisting of rigid bilayers than in the high-temperature Lalpha phase where the bilayers are more flexible. Various scenarios that may be responsible for this counterintuitive observation are discussed.
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Affiliation(s)
- T A Harroun
- Steacie Institute for Molecular Sciences, National Research Council, Chalk River, Ontario, Canada K0J 1J0
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Pan TC, Hsieh WJ, Chao CY. Thickness-dependent smectic- A–smectic- C*transition in chiral smectic free-standing liquid-crystal films. Phys Rev E 2004; 70:011706. [PMID: 15324071 DOI: 10.1103/physreve.70.011706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Indexed: 11/07/2022]
Abstract
We have conducted heat-capacity measurements near the smectic-A -smectic-C* phase transition in free-standing films of a chiral liquid-crystal compound. The heat-capacity behavior confirms the evolution of the transition in the interior layers from first to second order as a function of film thickness suggested earlier in tilt angle measurements. The asymmetry in the heat-capacity anomaly exhibits an interesting crossover in thinner films. We also observed the phase transitions leading to the crystallization to the tilted crystal-G phase in these films at lower temperatures. The surface ordering strength in these films is found to be much larger than that in other orthogonal-smectic films, which we speculate is due to the molecular tilt.
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Affiliation(s)
- Tung-Cheng Pan
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan, Republic of China
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Chao CY, Pan TC, Chou CF, Ho JT. Multiple electron diffraction and two-dimensional crystalline order in liquid-crystal thin films. PHYSICAL REVIEW LETTERS 2003; 91:125504. [PMID: 14525373 DOI: 10.1103/physrevlett.91.125504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2003] [Indexed: 05/24/2023]
Abstract
Electron diffraction in freestanding thin films in the crystal-B phase reveals extensive multiple diffraction in films of 14S5 but not of 4O.8, suggesting an important difference in the structural order in these films despite the similarities in their positional correlations found in earlier experiments. The result in a two-layer 14S5 film indicates surprisingly that secondary diffraction can occur in a crystal with only pseudo-long-range positional order.
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Affiliation(s)
- Chih-Yu Chao
- Department of Physics, National Taiwan University, Taipei 10617, Taiwan, Republic of China.
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de Jeu WH, Fera A, Konovalov O, Ostrovskii BI. Two-stage surface freezing of a single top layer in a smectic-A membrane. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:020701. [PMID: 12636645 DOI: 10.1103/physreve.67.020701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2002] [Indexed: 05/24/2023]
Abstract
The crystallization of a single liquid top layer of smectic membranes of the compound 4O.8 has been studied with grazing-incidence x-ray diffraction. As this process takes place in two steps, involving an intermediate hexatic smectic-B layer before the final crystalline-B surface structure is reached, it provides a model for melting in two dimensions. The positional order has been investigated quantitatively by measuring the scattering profiles and the associated correlation lengths. The surface liquid-hexatic phase transition is found to be continuous, while the hexatic-crystal transition is weakly first order with an abrupt change of the in-plane positional correlations. The surface phase transitions do not modify the liquid in-plane structure of the interior layers.
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Affiliation(s)
- Wim H de Jeu
- FOM-Institute AMOLF, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
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Chao CY, Lo CR, Wu PJ, Pan TC, Veum M, Huang CC, Surendranath V, Ho JT. Unusual thickness-dependent heat-capacity anomalies in free-standing hexatic liquid-crystal films. PHYSICAL REVIEW LETTERS 2002; 88:085507. [PMID: 11863962 DOI: 10.1103/physrevlett.88.085507] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2001] [Indexed: 05/23/2023]
Abstract
High-resolution heat-capacity and optical-reflectivity measurements have been conducted near the smectic-A to hexatic-B transition in thin free-standing films of the liquid-crystal compound 64COOBC. We find an unexpected dependence on film thickness of the integrated magnitude of the heat-capacity anomalies as the films undergo layer-by-layer transitions. We measure the penetration depths of the ordering from the surface and next-to-surface layers which are pertinent to the highly correlated thermal behavior.
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Affiliation(s)
- C Y Chao
- Department of Physics and Astronomy, National Central University, Chung-Li 32054, Taiwan, Republic of China.
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Chao CY, Liu YH, Pan TC, Chang BN, Ho JT. Direct layer-by-layer freezing of a smectic liquid-crystal surface into the crystalline phase. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:050703. [PMID: 11735887 DOI: 10.1103/physreve.64.050703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2001] [Indexed: 05/23/2023]
Abstract
Electron diffraction and optical reflectivity have provided the direct confirmation of the existence of layer-by-layer surface transitions from the smectic-A immediately to the crystal-B phase in a liquid-crystal material, without going through an intermediate hexatic phase. The molecular interactions are found to be through retarded van der Waals forces. Our results suggest that a smectic-A film can transform into a crystal-B through three possible scenarios.
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Affiliation(s)
- C Y Chao
- Department of Physics and Astronomy, National Central University, Chung-Li 32054, Taiwan, Republic of China.
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Chao CY, Pan TC, Chou CF, Ho JT. Structural characterization of surface hexatic behavior in free-standing 4O.8 liquid-crystal films. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:R1485-R1488. [PMID: 11088709 DOI: 10.1103/physreve.62.r1485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2000] [Indexed: 05/23/2023]
Abstract
Electron diffraction in free-standing liquid-crystal films of N-(4-n-butoxybenzylidene)-4-n-octylaniline between 3 and 12 molecular layers thick reveals the unusual occurrence of the smectic-A' phase, a highly correlated isotropic liquid, on the surface of smectic-A films. The surface smectic-A-smectic-A' transition is found to be first order. Surprisingly, the temperature range of the subsequent surface hexatic-B phase is reduced with decreasing film thickness.
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Affiliation(s)
- CY Chao
- Department of Physics, National Central University, Chung-Li, Taiwan 32054, Republic of China
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Chao CY, Lo CR, Ho JT. Crystalline transitions in free-standing films of 4-n-heptyloxybenzylidene-4-n-heptylaniline. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:5407-5409. [PMID: 11031591 DOI: 10.1103/physreve.61.5407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 02/03/2000] [Indexed: 05/23/2023]
Abstract
Free-standing films of 4-n-heptyloxybenzylidene-4-n-heptylaniline are known to exhibit multiple smectic-I surface layers in the presence of a smectic-A interior. The phase transitions leading to the crystallization of these films have been studied using electron diffraction. Our data are consistent with the scenario of the smectic-I surface layers first developing a crystal-B outermost layer before transforming entirely into the crystal-B phase, to be followed by the freezing of the smectic-A interior. The adjacent crystal-B and smectic-I layers show evidence of orientational epitaxy.
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Affiliation(s)
- CY Chao
- Department of Physics, National Central University, Chung-Li, Taiwan, Republic of China
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Fera A, Ostrovskii BI, Sentenac D, Samoilenko I, de Jeu WH. Layer-by-layer crystallization and the role of fluctuations in free standing smectic films. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:R5033-6. [PMID: 11970449 DOI: 10.1103/physreve.60.r5033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/1999] [Indexed: 04/18/2023]
Abstract
Specular x-ray reflectivity has been used to study the changes in the thermal fluctuation behavior of eight layer freely suspended N-(4-n-butoxybenzilidene)-4-n-octylaniline (4O.8) films during the process of successive layer-by-layer crystallizations. Each of these steps is preceded by the formation of an intermediate layer structure with in-plane hexatic ordering. We find an unusually large reduction of the fluctuations after the emergence of only the first hexatic toplayer. The fluctuation profiles over the film are in all cases quenched at the surfaces though less so after each crystallization step. This behavior supports theoretical arguments that hexatic order is reduced by out-of-plane smectic layer fluctuations.
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Affiliation(s)
- A Fera
- FOM-Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands
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RADHAKRISHNAN RAVI, GUBBINS KEITHE. Free energy studies of freezing in slit pores: an order-parameter approach using Monte Carlo simulation. Mol Phys 1999. [DOI: 10.1080/00268979909483070] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Sikes HD, Schwartz DK. Two-dimensional melting of an anisotropic crystal observed at the molecular level. Science 1997; 278:1604-7. [PMID: 9374455 DOI: 10.1126/science.278.5343.1604] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A distinctive two-dimensional (2D) melting transition occurring at nearly 100 degrees Celsius ( degrees C) has been observed in Langmuir-Blodgett films by in situ atomic force microscopy (AFM). A 2D orthorhombic crystal phase melted to a 2D smectic phase at about 91 degrees C. The smectic phase was characterized by 1D molecular periodicity with short-range correlations (about 40 angstroms). At 95 degrees C, the smectic order melted to form a hexatic phase. Infrared spectroscopy measurements were consistent with the AFM observations. These observations support the dislocation-mediated melting scenario for an anisotropic 2D crystal predicted by Ostlund and Halperin. A longer wavelength height modulation was also observed in the smectic and hexatic phases.
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Affiliation(s)
- HD Sikes
- Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
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