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Lehmann M, Maisch S, Scheuring N, Carvalho J, Cruz C, Sebastião PJ, Dong RY. From molecular biaxiality of real board-shaped mesogens to phase biaxiality? On the hunt for the holy grail of liquid crystal science. SOFT MATTER 2019; 15:8496-8511. [PMID: 31633147 DOI: 10.1039/c9sm01007f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
In the search of the predicted biaxial nematic phase, a series of shape-persistent board-shaped mesogens with maximum molecular biaxiality and a dipole along the minor molecular axis were designed to form nematic (N) mesophases. One compound exhibits a wide nematic temperature range, which can be supercooled to room temperature. A comprehensive variable temperature X-ray study on aligned samples reveals patterns being dominated by the form factor of very small aggregates, from which the aspect ratio of the lead compound with length (L) : breadth (B) : width (W) of 10.73 : 3.16 : 1.23 could be obtained. The ratio is close to the predicted optimum molecular biaxiality by Straley's hard particle model. Hence variable temperature proton relaxation studies on this mesogen were carried out over a wide frequency range. The global fit of the frequency dispersions at five temperatures with a motional model requires in addition to the usual rotation/reorientation contribution, two independent director fluctuations contributions: one for the conventional nematic order director (n) fluctuations and the other for the minor director (m) fluctuations (normal to n). The correlation length of the minor directors determined by NMR could extend to 5-8 molecules in the W direction, but only to the nearest neighbour in the B direction, as found by X-ray diffraction. Both X-ray and NMR studies indicate that these new types of lead structure are extremely promising to find the long sought-after biaxial N mesophase.
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Affiliation(s)
- Matthias Lehmann
- Institute of Organic Chemistry, University of Würzburg, Germany.
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2
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D'Urso C, Celebre G, Cinacchi G. Phase behavior of hard C_{2h}-symmetric particle systems. Phys Rev E 2019; 100:012709. [PMID: 31499787 DOI: 10.1103/physreve.100.012709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Indexed: 06/10/2023]
Abstract
Using Monte Carlo numerical simulation, this work sketches the phase diagram of systems of certain hard C_{2h}-symmetric particles, formed by gluing two aligned and displaced hard spherocylinders with a cylindrical-length-to-diameter ratio realistically, if viewed not only from the lyotropic colloidal liquid-crystal side but also from the thermotropic low-molecular-mass liquid-crystal side, equal to 5, as a function of the displacement. Several distinctive phases are observed, such as a nonperiodic smectic-B-like phase, a nonperiodic smectic-H-like phase, a smectic-C phase, and a short-layer-spacing uniaxial smectic-A phase but no biaxial nematic phase.
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Affiliation(s)
- Christian D'Urso
- Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, via P. Bucci, I-87036 Arcavacata di Rende (CS), Italy
| | - Giorgio Celebre
- Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, via P. Bucci, I-87036 Arcavacata di Rende (CS), Italy
| | - Giorgio Cinacchi
- Departamento de Física Teórica de la Materia Condensada, Instituto de Física de la Materia Condensada (IFIMAC), Instituto de Ciencias de Materiales "Nicolás Cabrera," Universidad Autónoma de Madrid, Ciudad Universitaria de Cantoblanco, E-28049 Madrid, Spain
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3
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Querciagrossa L, Berardi R, Zannoni C. Can off-centre mesogen dipoles extend the biaxial nematic range? SOFT MATTER 2018; 14:2245-2253. [PMID: 29485161 DOI: 10.1039/c8sm00067k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We have investigated the possibility of extending the stability range of the biaxial nematic phase by adding an off-centre dipole of various strengths and orientations to elongated biaxial Gay-Berne (GB) mesogens yielding a relatively narrow biaxial nematic (Nbx) phase, and a smectic (Sbx) phase when dipole-less. The effect of dipoles is not easy to predict, and our previous investigations have shown the limited benefits of having a central dipole. Here we show, employing molecular dynamics (MD) simulations, that a not too strong off-centre dipole positioned along the longest axis of the nematogen can extend the temperature range of stability of the biaxial nematic phase, also shifting it towards lower temperatures.
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Affiliation(s)
- Lara Querciagrossa
- Dipartimento di Chimica Industriale "Toso Montanari" and INSTM, Università di Bologna, Viale Risorgimento 4, IT-40136 Bologna, Italy.
| | - Roberto Berardi
- Dipartimento di Chimica Industriale "Toso Montanari" and INSTM, Università di Bologna, Viale Risorgimento 4, IT-40136 Bologna, Italy.
| | - Claudio Zannoni
- Dipartimento di Chimica Industriale "Toso Montanari" and INSTM, Università di Bologna, Viale Risorgimento 4, IT-40136 Bologna, Italy.
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4
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Querciagrossa L, Ricci M, Berardi R, Zannoni C. Can multi-biaxial mesogenic mixtures favour biaxial nematics? A computer simulation study. Phys Chem Chem Phys 2017; 19:2383-2391. [DOI: 10.1039/c6cp05117k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A mixture of mesogens with different anisotropies favours the biaxial nematic phase.
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Affiliation(s)
- Lara Querciagrossa
- Department of Industrial Chemistry “Toso Montanari”
- University of Bologna
- 40136 Bologna
- Italy
| | - Matteo Ricci
- Department of Industrial Chemistry “Toso Montanari”
- University of Bologna
- 40136 Bologna
- Italy
| | - Roberto Berardi
- Department of Industrial Chemistry “Toso Montanari”
- University of Bologna
- 40136 Bologna
- Italy
| | - Claudio Zannoni
- Department of Industrial Chemistry “Toso Montanari”
- University of Bologna
- 40136 Bologna
- Italy
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5
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Aliev MA, Ugolkova EA, Kuzminyh NY. The Landau-de Gennes free energy expansion of a melt of V-shaped polymer molecules. J Chem Phys 2016; 145:084908. [PMID: 27586947 DOI: 10.1063/1.4961662] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The phase behavior of a monodisperse melt of polymer molecules consisting of two rod-like segments joined at an angle α has been inspected within the Landau theory of phase transitions. The interactions between monomer units were assumed to be of the Maier-Saupe form. The Landau-de Gennes expansion of the free energy of the melt has been obtained up to the sixth order in powers of the nematic order parameter, the coefficients of this expansion have been calculated from the microscopic model of polymer molecule. The phase diagram contains the regions of stability of isotropic, prolate uniaxial, oblate uniaxial, and biaxial nematic phases. The isotropic-uniaxial nematic and uniaxial-biaxial nematic transitions are of the first and second order, respectively. We found two Landau points in the phase diagram at which continuous transition from biaxial nematic state to isotropic phase occurs.
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Affiliation(s)
- M A Aliev
- Institute of Biochemical Physics, 4, Kosygina St., 119334 Moscow, Russia
| | - E A Ugolkova
- Institute of General and Inorganic Chemistry, 31 Leninsky Pr., 119991 Moscow, Russia
| | - N Yu Kuzminyh
- Institute of Biochemical Physics, 4, Kosygina St., 119334 Moscow, Russia
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6
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Martín-Rapún R, Cano M, McKenna M, Serrano JL, Marcos M. Side-On Nematic Liquid Crystal Dendrimers Based on PAMAM and PPI as Dendritic Scaffolds: Synthesis and Characterization. MACROMOL CHEM PHYS 2015. [DOI: 10.1002/macp.201400598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Rafael Martín-Rapún
- Departamento de Química Orgánica; Facultad de Ciencias Instituto de Ciencia de Materiales de Aragón; Universidad de Zaragoza-CSIC; C/Pedro Cerbuna 12 50009 Zaragoza Spain
| | - Miguel Cano
- Departamento de Química Orgánica; Facultad de Ciencias Instituto de Ciencia de Materiales de Aragón; Universidad de Zaragoza-CSIC; C/Pedro Cerbuna 12 50009 Zaragoza Spain
| | - Mark McKenna
- Departamento de Química Orgánica; Facultad de Ciencias Instituto de Ciencia de Materiales de Aragón; Universidad de Zaragoza-CSIC; C/Pedro Cerbuna 12 50009 Zaragoza Spain
| | - José Luis Serrano
- Departamento de Química Orgánica; Facultad de Ciencias Instituto de Ciencia de Materiales de Aragón; Universidad de Zaragoza-CSIC; C/Pedro Cerbuna 12 50009 Zaragoza Spain
- Instituto de Nanociencia de Aragón; Mariano Esquillor edif. I+D; 50018 Zaragoza Spain
| | - Mercedes Marcos
- Departamento de Química Orgánica; Facultad de Ciencias Instituto de Ciencia de Materiales de Aragón; Universidad de Zaragoza-CSIC; C/Pedro Cerbuna 12 50009 Zaragoza Spain
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7
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Polineni S, Figueirinhas JL, Cruz C, Wilson DA, Mehl GH. Capacitance and optical studies of elastic and dielectric properties in an organosiloxane tetrapode exhibiting a N(B) phase. J Chem Phys 2013; 138:124904. [PMID: 23556748 DOI: 10.1063/1.4795582] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Biaxial (N(B)) and uniaxial nematic (N(U)) phase behavior was detected and confirmed for an organosiloxane tetrapode material using capacitance and birefringence measurements. Elastic constants, permittivities at two distinct low frequencies, and birefringencies were determined as a function of temperature over both the N(U) and the N(B) phase ranges. The N(U)-N(B) transition is clearly observed in the birefringencies and conoscopy data. A temperature dependent cross-over frequency is also detected in this material for the permittivities, allowing the electrical switching of both planar and homeotropic aligned samples.
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Affiliation(s)
- S Polineni
- IST-Technical University of Lisbon, Dept. de Física, Av. Rovisco Pais, P-1049-001 Lisboa, Portugal
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8
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Brömmel F, Kramer D, Brown BP, Finkelmann H, Hoffmann A. Orientability of the minor director of homeotropically aligned smectic-a elastomers in external mechanical fields. Macromol Rapid Commun 2013; 34:135-41. [PMID: 23112134 DOI: 10.1002/marc.201200588] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 10/03/2012] [Indexed: 11/07/2022]
Abstract
We present studies on bulk smectic-A copolymer networks with end-on attached homeotropically oriented mesogens that show spontaneous optical biaxiality at room temperature. Orthoscopic and conoscopic investigations under uniaxial extension in the layer planes give first evidence of the orientability of the minor director in mechanical fields yielding biaxial monodomains with 3-d orientational long-range order of all three principle axes. This is an important step towards the synthesis of permanently oriented biaxial monodomain elastomers for which highly interesting mechanical and optical properties are expected.
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9
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Querciagrossa L, Ricci M, Berardi R, Zannoni C. Mesogen polarity effects on biaxial nematics. Centrally located dipoles. Phys Chem Chem Phys 2013; 15:19065-72. [DOI: 10.1039/c3cp52970c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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10
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Matsuyama A. Novel biaxial nematic phases of side-chain liquid crystalline polymers. J Chem Phys 2012; 137:224906. [PMID: 23249031 DOI: 10.1063/1.4771592] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a mean field theory to describe biaxial nematic phases of side-chain liquid crystalline polymers, in which rigid side-chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. Taking into account both excluded volume and attractive interactions between rigid rods, novel biaxial nematic phases are theoretically predicted. We calculate uniaxial and biaxial orientational order parameters as a function of temperature and the length of backbone chains. We find a first-order biaxial-biaxial phase transition and a first (or second)-order uniaxial-biaxial one, depending on the length of mesogens and backbone chains.
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Affiliation(s)
- Akihiko Matsuyama
- Department of Bioscience and Bioinformatics, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Kawazu 680-4, Iizuka, Fukuoka 820-8502, Japan.
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11
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Domenici V. 2H NMR studies of liquid crystal elastomers: macroscopic vs. molecular properties. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2012; 63:1-32. [PMID: 22546343 DOI: 10.1016/j.pnmrs.2011.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 07/27/2011] [Indexed: 05/31/2023]
Affiliation(s)
- Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy.
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12
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Matsuyama A. Volume phase transitions of biaxial nematic elastomers. Phys Rev E 2012; 85:011707. [PMID: 22400583 DOI: 10.1103/physreve.85.011707] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Indexed: 11/07/2022]
Abstract
We present a mean-field theory to describe biaxial nematic phases of side-chain liquid crystalline elastomers. Novel biaxial nematic phases are theoretically predicted in a side-chain liquid crystalline polymer and gel, where side chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. We calculate uniaxial and biaxial orientational order parameters and examine deformations of the gel and stable biaxial nematic phases of the liquid crystalline gel dissolved in isotropic solvents. We predict first-order uniaxial-biaxial nematic phase transitions of the gel and the volume of the gel is discontinuously changed at the phase transition temperature.
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Affiliation(s)
- Akihiko Matsuyama
- Department of Bioscience and Bioinformatics, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Kawazu 680-4, Iizuka, Fukuoka 820-8502, Japan.
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13
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Figueirinhas JL, Feio G, Cruz C, Lehmann M, Köhn C, Dong RY. Nuclear magnetic resonance spectroscopic investigations of phase biaxiality in the nematic glass of a shape-persistent V-shaped mesogen. J Chem Phys 2010; 133:174509. [DOI: 10.1063/1.3496491] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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14
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Lehmann M, Köhn C, Figueirinhas J, Feio G, Cruz C, Dong R. Biaxial Nematic Mesophases from Shape-Persistent Mesogens with a Fluorenone Bending Unit. Chemistry 2010; 16:8275-9. [DOI: 10.1002/chem.201001214] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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15
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16
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De Matteis G, Romano S. Mesogenic lattice models with partly antinematic interactions producing uniaxial nematic phases. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:031702. [PMID: 19905126 DOI: 10.1103/physreve.80.031702] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Indexed: 05/28/2023]
Abstract
The present paper considers nematogenic lattice models, involving particles of D_{2h} symmetry, whose centers of mass are associated with a three-dimensional simple cubic lattice; the pair potential is isotropic in orientation space and restricted to nearest neighbors. Let two orthonormal triads define orientations of a pair of interacting particles; the simplest potential models proposed in the literature can be reduced to a linear combination involving the squares of the scalar products between corresponding unit vectors only and depending on three parameters. By now, various sets of potential parameters have been proposed and studied in the literature, some of which capable of producing biaxial orientational order at sufficiently low temperature. On the other hand, in experimental terms, mesogenic biaxial molecules mostly produce uniaxial mesophases; thus we address here two very simple cases, involving a nematic (calamitic) term as well as one (model P0M) or two (model PPM) antinematic ones, whose coefficients are set equal in magnitude; when only one antinematic coefficient is used, the third one is set to zero. The calamitic term favors the alignment of two corresponding molecular axes, whereas antinematic terms or geometric constraints tend to keep two other pairs of axes mutually orthogonal. The models were investigated by molecular-field treatments and Monte Carlo simulation and found to predict a first- or second-order transitions between uniaxial nematic and isotropic phases; the molecular-field treatments yielded results in reasonable agreement with simulation.
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Affiliation(s)
- Giovanni De Matteis
- Centro di Ricerca Matematica Ennio De Giorgi, Collegio Puteano, Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 3, I-56100 Pisa, Italy.
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17
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Storz R, Komp A, Hoffmann A, Finkelmann H. Phase Biaxility in Smectic-A Side-Chain Liquid Crystalline Elastomers. Macromol Rapid Commun 2009; 30:615-21. [DOI: 10.1002/marc.200800793] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Revised: 01/27/2009] [Accepted: 01/28/2009] [Indexed: 11/06/2022]
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18
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Dvinskikh SV, Yamamoto K, Scanu D, Deschenaux R, Ramamoorthy A. High-resolution characterization of liquid-crystalline [60]fullerenes using solid-state nuclear magnetic resonance spectroscopy. J Phys Chem B 2008; 112:12347-53. [PMID: 18781716 DOI: 10.1021/jp803265z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of fullerene-containing thermotropic compounds using solid-state natural abundance (13)C NMR experiments under stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic, liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional (13)C experiments, while two-dimensional separated local-field experiments were used to measure the (1)H- (13)C dipolar couplings in mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate fast around the symmetry axis on the characteristic NMR time scale of approximately 10 (-4) s.
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Affiliation(s)
- Sergey V Dvinskikh
- Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
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De Matteis G, Romano S. Biaxial and uniaxial phases produced by partly repulsive mesogenic models involving D2h molecular symmetries. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:021702. [PMID: 18850847 DOI: 10.1103/physreve.78.021702] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2007] [Revised: 04/22/2008] [Indexed: 05/26/2023]
Abstract
The present paper considers biaxial nematogenic lattice models, involving particles of D2h symmetry, whose centers of mass are associated with a three-dimensional simple-cubic lattice. The pair potential is isotropic in orientation space and restricted to nearest neighbors. Let two orthonormal triads define orientations of a pair of interacting particles. The investigated potential models are quadratic with respect to the nine scalar products between the two sets of unit vectors. Actually, based on available geometric identities, these expressions can be reduced to diagonal form containing only the scalar products between corresponding unit vectors and depending on three parameters. Over the years, this comparatively simple functional form has also proven to be rather versatile. By now, various sets of potential parameters capable of producing mesogenic behavior of some kind have been proposed and studied in the literature. A new and simplified form was recently proposed and investigated by Sonnet, Virga, Durand, and De Matteis [A. M. Sonnet, E. G. Virga, and G. E. Durand, Phys. Rev. E 67, 061701 (2003); G. De Matteis and E. G. Virga, Phys. Rev. E 71, 061703 (2005)] and is known to support a biaxial phase at sufficiently low temperature. Following the idea of the above authors, we have studied a more extended range of parameters, including cases where biaxiality cannot be sustained in the pair ground state. In cases where a biaxial phase survives, an appropriate mean-field analysis may predict the existence of a direct second-order transition to the isotropic phase as well as a second-order sequence isotropic-to-uniaxial-to-biaxial. A second-order phase transition is also predicted, which involves isotropic and uniaxial phases only. Monte Carlo simulations have been carried out as well, for a few points in the parameter space, and found to produce results which partly confirm mean-field predictions.
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Affiliation(s)
- Giovanni De Matteis
- Centro di Ricerca Matematica Ennio De Giorgi, Collegio Puteano, Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 3, I-56100 Pisa, Italy.
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Bisi F, Rosso R, Virga EG, Durand GE. Polar steric interactions for V-shaped molecules. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:011705. [PMID: 18763971 DOI: 10.1103/physreve.78.011705] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2007] [Revised: 04/01/2008] [Indexed: 05/26/2023]
Abstract
We consider the effect of shape polarity in the excluded-volume interaction between V -shaped polar particles in orientationally ordered phases. We show that the polar component of the steric interaction between these polar particles, large enough in two space dimensions, can also become important in three space dimensions. Unexpectedly, polar steric interactions, up to now neglected, favor an "antiparallel" pair binding, which may be the building block of orientationally ordered phases for polar particles. An antiferromorphic smectic ordering, which is also antiferroelectric, could further be attained at high enough density by the same mechanism.
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Affiliation(s)
- Fulvio Bisi
- Dipartimento di Matematica and CNISM, Università di Pavia, Via Ferrata 1, Pavia, Italy
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21
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Cordoyiannis G, Apreutesei D, Mehl GH, Glorieux C, Thoen J. High-resolution calorimetric study of a liquid crystalline organo-siloxane tetrapode with a biaxial nematic phase. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:011708. [PMID: 18763974 DOI: 10.1103/physreve.78.011708] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Indexed: 05/26/2023]
Abstract
High-resolution adiabatic scanning calorimetry and differential scanning calorimetry have been employed to study the thermal behavior of an organo-siloxane tetrapode reported to exhibit a biaxial nematic phase. No signature of the uniaxial to biaxial nematic phase transition could be retraced in sequential heating and cooling runs under different scanning rates, within the experimental resolution. The results obtained reveal that an extremely small heat should be involved in the uniaxial to biaxial nematic phase transition. The isotropic to uniaxial nematic transition at 318+/-0.01 K is very stable, and it is weakly first order with a rather small latent heat of 0.20+/-0.02 J/g .
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Affiliation(s)
- George Cordoyiannis
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, Leuven, Belgium
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Skacej G, Zannoni C. Biaxial liquid-crystal elastomers: a lattice model. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2008; 25:181-186. [PMID: 18357411 DOI: 10.1140/epje/i2007-10280-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Accepted: 01/28/2008] [Indexed: 05/26/2023]
Abstract
We present a simple coarse-grained lattice model for monodomain biaxial liquid-crystal elastomers and perform large-scale Monte Carlo simulations in the proposed model system. Orientational ordering--uniaxial or biaxial--reflects in sample deformations on cooling the system. The simulation output is used to predict calorimetry data and deuterium magnetic resonance spectra.
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Affiliation(s)
- G Skacej
- Fakulteta za matematiko in fiziko, Univerza v Ljubljani, Jadranska 19, SI-1000, Ljubljana, Slovenia.
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23
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High nematic ordering in a bent-core smectogen showing a biaxial nematic phase: A 13C NMR study. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.09.070] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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24
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Bisi F, Romano S, Virga EG. Uniaxial rebound at the nematic biaxial transition. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:041705. [PMID: 17500911 DOI: 10.1103/physreve.75.041705] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Revised: 01/20/2007] [Indexed: 05/15/2023]
Abstract
Over the last few years, renewed interest has been raised by the simplified general interaction models proposed by Straley for mesogenic molecules possessing the D{2h} symmetry and capable of producing biaxial nematic order. It has already been shown that, in the presence of certain special symmetries, just two out of the four order parameters that are in general necessary, suffice for the description of a biaxial phase. For some other range of parameters, these reducing symmetries do not hold, and, moreover, a mean-field treatment has to be suitably changed into a minimax strategy, still producing a transition to a low-temperature biaxial phase. Upon studying the general parameter range, we identify as a common feature the behavior of a uniaxial order parameter, attaining a local minimum at the biaxial-to-uniaxial transition temperature, and recognizably increasing away from it. This finding is confirmed by a Monte Carlo simulation.
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Affiliation(s)
- Fulvio Bisi
- Dipartimento di Matematica and CNISM, Università di Pavia, via Ferrata 1, I-27100 Pavia, Italy
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