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Jasiurkowska-Delaporte M, Juszyńska-Gałązka E, Zieliński PM, Marzec M. Studies of molecular dynamics and non-isothermal crystallization process of 4-n-butyloxybenzylidene-4′-n'-octylaniline (BBOA) liquid crystal under two dimensional nano-confinement. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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2
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Całus S, Borowik L, Kityk AV, Eich M, Busch M, Huber P. Thermotropic interface and core relaxation dynamics of liquid crystals in silica glass nanochannels: a dielectric spectroscopy study. Phys Chem Chem Phys 2015; 17:22115-24. [PMID: 26255586 DOI: 10.1039/c5cp03039k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the cyanobiphenyl family (5CB and 6CB) confined in tubular nanochannels with 7 nm radius and 340 micrometer length in a monolithic, mesoporous silica membrane. The measurements were performed on composites for two distinct regimes of fractional filling: monolayer coverage at the pore walls and complete filling of the pores. For the layer coverage a slow surface relaxation dominates the dielectric properties. For the entirely filled channels the dielectric spectra are governed by two thermally-activated relaxation processes with considerably different relaxation rates: a slow relaxation in the interface layer next to the channel walls and a fast relaxation in the core region of the channel filling. The strengths and characteristic frequencies of both relaxation processes have been extracted and analysed as a function of temperature. Whereas the temperature dependence of the static capacitance reflects the effective (average) molecular ordering over the pore volume and is well described within a Landau-de Gennes theory, the extracted relaxation strengths of the slow and fast relaxation processes provide an access to distinct local molecular ordering mechanisms. The order parameter in the core region exhibits a bulk-like behaviour with a strong increase in the nematic ordering just below the paranematic-to-nematic transition temperature TPN and subsequent saturation during cooling. By contrast, the surface ordering evolves continuously with a kink near TPN. A comparison of the thermotropic behaviour of the monolayer with the complete filling reveals that the molecular order in the core region of the pore filling affects the order of the peripheral molecular layers at the wall.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
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Całus S, Kityk AV, Eich M, Huber P. Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid. SOFT MATTER 2015; 11:3176-3187. [PMID: 25759093 DOI: 10.1039/c5sm00108k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report filling-fraction dependent dielectric spectroscopy measurements on the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica nanochannels. In the film-condensed regime, a slow interface relaxation dominates the dielectric spectra, whereas from the capillary-condensed state up to complete filling an additional, fast relaxation in the core of the channels is found. The temperature-dependence of the static capacitance, representative of the averaged, collective molecular orientational ordering, indicates a continuous, paranematic-to-nematic (P-N) transition, in contrast to the discontinuous bulk behaviour. It is well described by a Landau-de-Gennes free energy model for a phase transition in cylindrical confinement. The large tensile pressure of 10 MPa in the capillary-condensed state, resulting from the Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts for a downward-shift of the P-N transition and an increased molecular mobility in comparison to the unstretched liquid state of the complete filling. The strengths of the slow and fast relaxations provide local information on the orientational order: the thermotropic behaviour in the core region is bulk-like, i.e. it is characterized by an abrupt onset of the nematic order at the P-N transition. By contrast, the interface ordering exhibits a continuous evolution at the P-N transition. Thus, the phase behaviour of the entirely filled liquid crystal-silica nanocomposite can be quantitatively described by a linear superposition of these distinct nematic order contributions.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, Al. Armii Krajowej 17, 42-200 Czestochowa, Poland.
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Mirzaei J, Urbanski M, Kitzerow HS, Hegmann T. Hydrophobic gold nanoparticles via silane conjugation: chemically and thermally robust nanoparticles as dopants for nematic liquid crystals. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2013; 371:20120256. [PMID: 23459959 DOI: 10.1098/rsta.2012.0256] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We examine for the first time how chemically and thermally stable gold nanoparticles (NPs), prepared by a silane conjugation approach, affect both the thermal and the electro-optical properties of a nematic liquid crystal (LC), when doped at concentrations ranging from 0.25 to 7.5 wt%. We find that the octadecylsilane-conjugated gold NPs stabilize both the enantiotropic nematic and the monotropic smectic-A phases of the LC host with a maximum stabilization of 2(°)C for the nematic and 3.5(°)C for the smectic-A phases for the mixture containing 1 wt% of the silanized particles. The same mixture shows the lowest values for the Fréedericksz transition threshold voltage and the highest value for the dielectric anisotropy. Generally, all NP-containing mixtures, except mixtures with NP concentrations exceeding 5 wt%, reduce the threshold voltage, increase the dielectric anisotropy and reduce both rise and decay time; the latter particularly at temperatures at least 10(°)C below the isotropic-nematic phase transition on cooling.
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Affiliation(s)
- Javad Mirzaei
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
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Rzoska SJ, Pawlus S, Czupryński K. Glassy dynamics in the isotropic phase of a smectogenic liquid crystalline compound. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 84:031710. [PMID: 22060393 DOI: 10.1103/physreve.84.031710] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Revised: 07/29/2011] [Indexed: 05/31/2023]
Abstract
The temperature evolution of the primary relaxation time in the isotropic phase of 4-cyano-4'-tetradecylbiphenyl (14CB) above the isotropic-smectic A (I-SmA) transition is discussed. Based on the enthalpy space and distortion-sensitive analysis, the prevalence of the mode coupling theory (MCT) "critical" and "glassy" dynamics is shown. The obtained singular dependence is related to the MCT critical temperature located approximately 48 K below the clearing (I-SmA) temperature. However, a weak but detectable distortion in the immediate vicinity of the transition occurs. It is also shown that the value of the fragile strength coefficient D(T) is characteristic of a very fragile glassy liquid whereas the steepness index m is typical of a strong one. Both magnitudes anomalously change on approaching the I-SmA phase transition. The static permittivity shows the pretransitional effect linked to the temperature of the hypothetical continuous phase transition located approximately 10.2 K below the I-SmA transition.
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Affiliation(s)
- Sylwester J Rzoska
- Institute of High Pressure Physics, Polish Academy of Sciences, ulica Sokołowska 27/39, PL-00-143 Warsaw, Poland.
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Chen Z, Nozaki R. Does transparent nematic phase exist in 5CB/DDAB/water microemulsions? From the viewpoint of temperature dependent dielectric spectroscopy. J Chem Phys 2011; 134:034505. [DOI: 10.1063/1.3530782] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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7
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Sigdel KP, Iannacchione GS. Study of the isotropic to smectic-A phase transition in liquid crystal and acetone binary mixtures. J Chem Phys 2010; 133:174501. [PMID: 21054045 DOI: 10.1063/1.3502112] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The first-order transition from the isotropic (I) to smectic-A (Sm A) phase in the liquid crystal 4-cyano-4(')-decylbiphenyl (10CB) doped with the polar solvent acetone (ace) has been studied as a function of solvent concentration by high-resolution ac-calorimetry. Heating and cooling scans were performed for miscible 10CB+ace samples having acetone mole fractions from x(ace)=0.05 (1 wt %) to 0.36 (10%) over a wide temperature range from 310 to 327 K. Two distinct first-order phase transition features are observed in the mixture whereas there is only one transition (I-Sm A) in the pure 10CB for that particular temperature range. Both calorimetric features reproduce on repeated heating and cooling scans and evolve with increasing x(ace) with the high-temperature feature relatively stable in temperature but reduced in size while the low-temperature feature shifts dramatically to lower temperature and exhibits increased dispersion. The coexistence region increases for the low-temperature feature but remains fairly constant for the high-temperature feature as a function of x(ace). Polarizing optical microscopy supports the identification of a smectic phase below the high-temperature heat capacity signature indicating that the low-temperature feature represents an injected smectic-smectic phase transition. These effects may be the consequence of screening the intermolecular potential of the liquid crystals by the solvent that stabilizes a weak smectic phase intermediate of the isotropic and pure smectic-A.
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Affiliation(s)
- Krishna P Sigdel
- Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, USA
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Chahine G, Kityk AV, Démarest N, Jean F, Knorr K, Huber P, Lefort R, Zanotti JM, Morineau D. Collective molecular reorientation of a calamitic liquid crystal (12CB) confined in alumina nanochannels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:011706. [PMID: 20866634 DOI: 10.1103/physreve.82.011706] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Indexed: 05/29/2023]
Abstract
We study the smectic director structure of the rodlike liquid crystal 4-n-dodecyl-4'-cyanobiphenyl (12CB) confined in cylindrical cavities of 200 nm diameter in porous alumina templates by means of combined broadband dielectric spectroscopy, optical birefringence, and neutron scattering measurements. We show that the collective molecular orientation differs between entering the smectic A phase upon cooling from the isotropic state and entering the same phase upon heating while melting the confined crystal. We discuss this collective molecular realignment in terms of a competition between weak planar anchoring at the p-Al2O3/12CB interface and a preferred texture typical of the crystallization of rodlike molecules in nanochannels (Bridgman growth).
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Affiliation(s)
- Gilbert Chahine
- Institut de Physique de Rennes, UMR 6251, Université de Rennes 1, 35042 Rennes, France
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de la Fuente MR, López DO, Pérez-Jubindo MA, Dunmur DA, Diez-Berart S, Salud J. Cylindrical sub-micrometer confinement results for the odd-symmetric dimer alpha,omega-bis[(4-cyanobiphenyl)-4'-yloxy]undecane (BCB.O11). J Phys Chem B 2010; 114:7864-73. [PMID: 20496880 DOI: 10.1021/jp9121084] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Broadband dielectric spectroscopy (10(2) Hz to 1.9 x 10(9) Hz) and specific heat measurements have been performed on the odd-symmetric dimer alpha,omega-bis[(4-cyanobiphenyl)-4'-yloxy]undecane (BCB.O11) in the isotropic (I) and nematic (N) phases confined to 200 nm diameter parallel cylindrical pores of Anopore membranes. Unlike previous studies on liquid crystal monomers, untreated and hexadecyltrimethylammonium bromide-treated membranes give rise to radial and axial confinements, respectively. An attempt is made to explain these unexpected results by means of a qualitative model for the dimer arrangement on alumina substrates. The model suggests that the population of conformers, which follow the bulk-like dynamics, is modified by confinement. Such a fact seems to be consistent with other distinctive features attributed to confinement, as for example, the increasing of the entropy change at the N-to-I phase transition for both axial and radial confinements. Specific-heat measurements have shown how confinement affects the N-to-I phase transition by a downward shift in transition temperature as well as by broadened and rounded specific-heat peaks. However, these modifications are revealed to be substantially different from what has been found previously in similar studies on liquid crystal monomers. Dynamic dielectric measurements have probed the different molecular motions in both confinements and how these motions are developed in a way similar to the bulk-dimer. Dielectric results have also proved that the surface-pinned molecular layer (where molecular motions are very restricted) adjacent to the pore-wall is temperature-dependent as already found previously for liquid crystal monomers.
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Affiliation(s)
- M R de la Fuente
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
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Brás AR, Frunza S, Guerreiro L, Fonseca IM, Corma A, Frunza L, Dionísio M, Schönhals A. Molecular mobility of nematic E7 confined to molecular sieves with a low filling degree. J Chem Phys 2010; 132:224508. [DOI: 10.1063/1.3432775] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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11
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Frunza S, Schönhals A, Frunza L, Beica T, Zgura I, Ganea P, Stoenescu D. Dynamics of cyanophenyl alkylbenzoate molecules in the bulk and in a surface layer adsorbed onto aerosil. Variation of the lengths of the alkyl chain. Chem Phys 2010. [DOI: 10.1016/j.chemphys.2010.04.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Kinkead B, Hegmann T. Effects of size, capping agent, and concentration of CdSe and CdTequantum dots doped into a nematic liquid crystal on the optical and electro-optic properties of the final colloidal liquid crystal mixture. ACTA ACUST UNITED AC 2010. [DOI: 10.1039/b911641a] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Drozd-Rzoska A. Universal pattern for the distribution of relaxation times in the isotropic phase of liquid crystalline n-cyanobiphenyls. Phys Rev E 2009; 80:011704. [PMID: 19658715 DOI: 10.1103/physreve.80.011704] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2009] [Revised: 05/15/2009] [Indexed: 11/07/2022]
Abstract
A universal pattern emerging from the analysis of the distribution of relaxation times in the isotropic phase of liquid crystalline n-alkylcyanobiphenyls (nCB) from 4CB to 14CB is presented. The increase of the length of nCB molecules causes the high-frequency (short-time) branch of the primary relaxation loss curve to approach the form epsilon(f>fpeak) approximately omega(-n), with n-->1/2 in frequency (omega=2pif) or approximately sqrt[t] in time on cooling toward the isotropic-mesophase "clearing" phase-transition temperature (TC). Recently, such behavior was suggested as a hypothetical universal pattern for diverse glass forming organic liquids on approaching the glass temperature [A. I. Nielsen, T. Christensen, B. Jakobsen, K. Niss, N. B. Olsen, R. Richert, and J. C. Dyre, J. Chem. Phys. 130, 154508 (2009)]. The isotropic phase of rodlike liquid crystalline compounds is considered to be an important experimental model system for studying glassy dynamics since it constitutes a link with the model fluid of hard ellipsoids of revolution.
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Kundu SK, Okudaira S, Kosuge M, Shinyashiki N, Yagihara S. Phase Transition and Abnormal Behavior of a Nematic Liquid Crystal in Benzene. J Phys Chem B 2009; 113:11109-14. [DOI: 10.1021/jp903391z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Shyamal Kumar Kundu
- Department of Physics, School of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
| | - Shun Okudaira
- Department of Physics, School of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
| | - Masanori Kosuge
- Department of Physics, School of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
| | - Naoki Shinyashiki
- Department of Physics, School of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
| | - Shin Yagihara
- Department of Physics, School of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan
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Garland CW, Iannacchione GS. Effect of Aerosil Gels on de Gennes Nematic−Smectic Coupling. J Phys Chem B 2008; 113:3901-5. [DOI: 10.1021/jp805525y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- C. W. Garland
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609
| | - G. S. Iannacchione
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609
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Kundu SK, Okudaira S, Kosuge M, Shinyashiki N, Yagihara S. Broadband dielectric spectroscopy of a nematic liquid crystal in benzene. J Chem Phys 2008; 129:164509. [DOI: 10.1063/1.2993255] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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17
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Lefort R, Morineau D, Guégan R, Guendouz M, Zanotti JM, Frick B. Relation between static short-range order and dynamic heterogeneities in a nanoconfined liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 78:040701. [PMID: 18999369 DOI: 10.1103/physreve.78.040701] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Indexed: 05/27/2023]
Abstract
We analyze the molecular dynamics heterogeneity of the liquid crystal 4-n-octyl-4'-cyanobiphenyl nanoconfined in porous silicon. We show that the temperature dependence of the dynamic correlation length xi_(wall) , which measures the distance over which a memory of the interfacial slowing down of the molecular dynamics persists, is closely related to the growth of the short-range static order arising from quenched random fields. More generally, this result may also shed some light on the connection between static and dynamic heterogeneities in a wide class of condensed and soft matter systems.
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Affiliation(s)
- Ronan Lefort
- Institut de Physique de Rennes (IPR), CNRS-UMR 6251, Université de Rennes 1, Rennes, France
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Brás AR, Dionísio M, Schönhals A. Confinement and Surface Effects on the Molecular Dynamics of a Nematic Mixture Investigated by Dielectric Relaxation Spectroscopy. J Phys Chem B 2008; 112:8227-35. [DOI: 10.1021/jp802133e] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A. R. Brás
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Federal Institute of Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
| | - M. Dionísio
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Federal Institute of Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
| | - A. Schönhals
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Federal Institute of Materials Research and Testing (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
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Pérez-Jubindo MA, de la Fuente MR, Diez-Berart S, López DO, Salud J. Influence of Cylindrical Submicrometer Confinement on the Static and Dynamic Properties in Nonyloxycyanobiphenyl (9OCB). J Phys Chem B 2008; 112:6567-77. [DOI: 10.1021/jp800119s] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. A. Pérez-Jubindo
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - M. R. de la Fuente
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - S. Diez-Berart
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - D. O. López
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
| | - J. Salud
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain, Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Diagonal 647, E.T.S.I.B., 08028 Barcelona, Spain, and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, U.S.A
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Cusmin P, Fuente MRDL, Salud J, Pérez-Jubindo MA, Diez-Berart S, López DO. Critical Behavior and Scaling Relationships at the SmAd−N and N−I Transitions in Nonyloxycyanobiphenyl (9OCB). J Phys Chem B 2007; 111:8974-84. [PMID: 17616221 DOI: 10.1021/jp070689v] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Different kind of measurements were performed on the liquid crystal nonyloxycyanobiphenyl (9OCB) to carry out a study of the molecular dynamics in the smectic A (SmA), nematic (N), and isotropic (I) phases as well as an exhaustive analysis of both the SmA-to-N and N-to-I phase transitions. For the dynamic study, broadband dielectric spectroscopy (102 to 1.8 x 109 Hz) was used. Two orientations (parallel and perpendicular) of the molecular director with regard to the probing electric field were investigated. From this study, the static dielectric permittivity was obtained in both alignments and, in addition, the molecular motions that contribute to each one were discussed. The static dielectric data together with specific heat and volumetric determinations were analyzed, proving that both phase transitions are weakly first order, displaying a nearly tricritical behavior. However, the width of metastable regions seems to be dependent on the physical magnitude, although specific heat and volumetric determinations allow for comparable results. It should be noticed that the temperature derivative of the static dielectric permittivity, specific heat, and isobaric thermal expansion coefficient data derived from volumetric determinations are related to each other by scaling relationships.
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Affiliation(s)
- P Cusmin
- Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, ETSEIB, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Spain
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Zhang Z, van Duijneveldt JS. Effect of suspended clay particles on isotropic-nematic phase transition of liquid crystal. SOFT MATTER 2007; 3:596-604. [PMID: 32900023 DOI: 10.1039/b613327d] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Sterically stabilised nano-platelets were prepared by treating montmorillonite clay with both a surfactant and a polymeric stabiliser. These nano-platelets formed stable suspensions in a thermotropic liquid crystal, 5CB. This is in marked contrast with previous work on preparing liquid crystal suspensions of either spheres, which formed gels on cooling the solvent into the nematic phase, or clay platelets stabilised only with low molecular weight surfactant, which tended to aggregate. In the isotropic state of the liquid crystal, static light scattering showed that the clay nano-platelets were freely suspended, and no aggregation was detected even after repeated temperature cycling into and out of the nematic phase. Small-angle X-ray scattering showed that the clay was delaminated nearly completely in the liquid crystal, with some stacks of a few clay nano-platelets having formed. Differential scanning calorimetry of the liquid crystal/clay suspensions showed a small but non-monotonic shift of the transition temperature compared to that of the pure liquid crystal. This behaviour is similar to that of liquid crystal confined in porous media, with an initial increase of the transition temperature on adding clay being ascribed to the effect of surface anchoring facilitating the formation of the nematic phase, whereas a decrease at higher clay concentrations (or equivalently, for smaller pores) is ascribed to confinement effects frustrating the formation of the nematic phase. This interpretation is supported by polarising light microscopy which showed the nematic domain size becoming smaller on increasing the clay concentration.
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Affiliation(s)
- Zexin Zhang
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, UKBS8 1TS.
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Liang D, Leheny RL. Smectic liquid crystals in an anisotropic random environment. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:031705. [PMID: 17500709 DOI: 10.1103/physreve.75.031705] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2006] [Indexed: 05/15/2023]
Abstract
We report a high-resolution x-ray scattering study of the smectic liquid crystal octylcyanobiphenyl (8CB) confined to aligned colloidal aerosil gels. The aligned gels introduce orientational fields that promote long-range nematic order while imposing positional random fields that couple to the smectic density wave and disrupt the formation of an ordered smectic phase. At low densities of aerosil, the low-temperature scattering intensity is consistent with the presence of a topologically ordered XY Bragg glass phase that is predicted to form in response to such anisotropic quenched disorder. The observed features of the phase include an algebraic decay of the smectic correlations, which is truncated at large length scales due to the imperfect nematic order, and a power-law exponent that agrees closely with the universal value predicted for the XY Bragg glass. At higher aerosil densities, deviations from the XY Bragg glass form are apparent. At high temperature, the scattering intensity displays pretransitional dynamic fluctuations associated with the destroyed nematic to smectic-A transition. The fluctuations obey quasicritical behavior over an extended range of reduced temperature. The effective critical exponents for the correlation lengths and smectic susceptibility differ systematically from those of pure 8CB, indicating that coupling of the nematic order to the gel suppresses its role in the smectic critical behavior.
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Affiliation(s)
- Dennis Liang
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
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Popa-Nita V, van der Schoot P, Kralj S. Influence of a random field on particle fractionation and solidification in liquid-crystal colloid mixtures. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2006; 21:189-97. [PMID: 17186160 DOI: 10.1140/epje/i2006-10059-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2006] [Accepted: 11/24/2006] [Indexed: 05/13/2023]
Abstract
The influence of a random-anisotropy (RA) type disorder on the phase separation of nematogen-colloid mixtures is studied theoretically by combining the phenomenological Landau-de Gennes, Carnahan-Starling, and hard-sphere crystal theories. We assume that the colloids enforce the RA disorder on the surrounding thermotropic liquid-crystal (LC) molecules. We adopt the Imry-Ma argument according to which the lower-temperature phase exhibits a domain-type pattern. The colloids impose a finite degree of orientational ordering even in the isotropic (paranematic) phase. In the ordered phase they give rise to a domain-type structure, resulting in the distorted nematic (speronematic) phase. The RA field opposes the phase separation tendency. With increasing disorder the difference between the paranematic and speronematic ordering decreases. Consequently there is a critical disorder, above which both phases become identical from the orientation point of view, but have different concentrations of colloids. We have also estimated another characteristic value of disorder above which the isotropic phase can exist only in a liquid state, the crystal phase being suppressed completely.
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Affiliation(s)
- V Popa-Nita
- Faculty of Physics, University of Bucharest, P.O. Box MG-11, 077125 Bucharest, Romania.
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Brás ARE, Viciosa MT, Rodrigues CM, Dias CJ, Dionísio M. Changes in molecular dynamics upon formation of a polymer dispersed liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:061709. [PMID: 16906851 DOI: 10.1103/physreve.73.061709] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2005] [Revised: 01/13/2006] [Indexed: 05/11/2023]
Abstract
The molecular dynamics during the formation of a polymer dispersed liquid crystal (PDLC) was followed by dielectric relaxation spectroscopy in the frequency range from 10(-1) to 2 x 10(6) Hz and over the temperature range from 158 to 273 K. The composite was produced by thermal polymerization induced phase separation of a mixture of triethyleneglycol dimethacrylate and the nematic liquid crystal, E7, in the proportion of 60:40 w/w. Both monomer and liquid crystal vitrify upon cooling having glass transition relaxation processes already characterized by some of us; yet E7 was previously studied in a narrower frequency range, so the present work updates its dielectric behavior. The starting mixture exhibits a rather complex dielectric spectrum due to the detection of multiple processes occurring simultaneously in the monomer and liquid crystal constituents. The PDLC formation occurs by mobility changes essentially in the liquid crystal tumbling motion, while the main relaxation of the monomer depletes upon polymerization. A low intense secondary process of E7 hardly detected in the bulk material is enhanced in both starting mixture and final composite allowing its characterization.
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Affiliation(s)
- Ana R E Brás
- REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
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On the influence of cylindrical sub-micrometer confinement on heptyloxycyanobiphenyl (7OCB). A dynamic dielectric study. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.03.072] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Diez S, López DO, de la Fuente MR, Pérez-Jubindo MA, Salud J, Tamarit JL. Thermodynamic and dielectric studies concerning the influence of cylindrical submicrometer confinement on heptyloxycyanobiphenyl. J Phys Chem B 2005; 109:23209-17. [PMID: 16375284 DOI: 10.1021/jp054124f] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Measurements of the specific heat and the static dielectric permittivity of heptyloxycyanobiphenyl (7OCB) confined to the 0.2 microm diameter parallel cylindrical pores of Anopore membranes in the isotropic phase and nematic mesophase, are presented. A comparison between the bulk and the confined 7OCB in treated and untreated pore wall surfaces using a chemical surfactant (HTBA) is performed. Both the treated and untreated membrane confinements seem to affect the nematic-to-isotropic phase transition by a downshift in transition temperature and some rounding at the specific-heat maximum, in a way similar to that which was earlier published for other liquid crystals confined in the same geometry. The static dielectric measurements clearly point out that untreated membrane confinement is axial, with the nematic director aligned parallel to the pore axis being homeotropic bulklike, i.e., with the nematic director aligned perpendicular to the electrode cell surfaces. After chemical surfactant treatment, the nematic director is constrained in a radial alignment being perpendicular to the pore walls. The dielectric measurements are revealed to be specially sensible to analyze the surface-induced nematic order due to the pore wall. The tricritical nature of the nematic-to-isotropic phase transition in bulk 7OCB as well as in treated and untreated Anopore confined geometries is discussed through both the specific heat and the static dielectric data.
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Affiliation(s)
- S Diez
- Laboratori de Caracterització de Materials (LCM), Departament de Física i Enginyeria Nuclear, ETSEIB, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Spain
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