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Kyrou C, Kralj S, Panagopoulou M, Raptis Y, Nounesis G, Lelidis I. Impact of spherical nanoparticles on nematic order parameters. Phys Rev E 2018; 97:042701. [PMID: 29758630 DOI: 10.1103/physreve.97.042701] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Indexed: 06/08/2023]
Abstract
We study experimentally the impact of spherical nanoparticles on the orientational order parameters of a host nematic liquid crystal. We use spherical core-shell quantum dots that are surface functionalized to promote homeotropic anchoring on their interface with the liquid crystal host. We show experimentally that the orientational order may be strongly affected by the presence of spherical nanoparticles even at low concentrations. The orientational order of the composite system is probed by means of polarized micro-Raman spectroscopy and by optical birefringence measurements as function of temperature and concentration. Our data show that the orientational order depends on the concentration in a nonlinear way, and the existence of a crossover concentration χ_{c}≈0.004pw. It separates two different regimes exhibiting pure-liquid crystal like (χ<χ_{c}) and distorted-nematic ordering (χ>χ_{c}), respectively. In the latter phase the degree of ordering is lower with respect to the pure-liquid crystal nematic phase.
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Affiliation(s)
- C Kyrou
- Faculty of Physics, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos, Athens 157 84, Greece
| | - S Kralj
- Faculty of Natural Sciences and Mathematics, University of Maribor, 2000 Maribor, Slovenia
| | - M Panagopoulou
- Physics Department, National Technical University of Athens, Heroon Polytechniou 9, 15780 Zographou, Athens, Greece
| | - Y Raptis
- Physics Department, National Technical University of Athens, Heroon Polytechniou 9, 15780 Zographou, Athens, Greece
| | - G Nounesis
- Biomolecular Physics Laboratory, National Centre for Scientific Research Demokritos, Aghia Paraskevi, Greece
| | - I Lelidis
- Faculty of Physics, National and Kapodistrian University of Athens, Panepistimiopolis, Zografos, Athens 157 84, Greece
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Kocot A, Vij JK, Perova TS, Merkel K, Swaminathan V, Sreenilayam SP, Yadav N, Panov VP, Stevenson PJ, Panov A, Rodriguez-Lojo D. Observation of the de Vries behavior in SmA * phase of a liquid crystal using polarised Raman scattering and infrared spectroscopy. J Chem Phys 2017; 147:094903. [PMID: 28886626 DOI: 10.1063/1.4999792] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Two approaches exist in the literature for describing the orientational distribution function (ODF) of the molecular directors in SmA* phase of liquid crystals, though several models are recently proposed in the literature for explaining the de Vries behaviour. These ODFs correspond to either the conventional unimodal arrangements of molecular directors arising from the mean field theory that leads to the broad or sugar-loaf like distribution or to the "diffuse-cone-shaped" type distribution proposed by de Vries. The hypothesis by de Vries provides for a realistic explanation as to how at a molecular level, a first-order SmA* to SmC* transition can occur where the uniform molecular director azimuthal distributions condense to values lying within a narrow range of angles; finally these condense to a single value while at the same time ensuring a little or no concomitant shrinkage in the layer spacing. The azimuthal distribution of the in-layer directors is probed using IR and polarized Raman spectroscopic techniques. The latter allows us to obtain the ODF and the various order parameters for the uniaxial and the biaxial phases. Based on the results of these measurements, we conclude that the "cone-shaped" (or volcano-shaped) de Vries type of distribution can most preferably describe SmA* where "a first-order phase transition from SmA* to SmC*" and a low layer shrinkage can both be easily explained.
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Affiliation(s)
- A Kocot
- Institute of Physics, Silesian University, Katowice, Poland
| | - J K Vij
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - T S Perova
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - K Merkel
- Central Mining Institute, Katowice, Poland
| | - V Swaminathan
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - S P Sreenilayam
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - N Yadav
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - V P Panov
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - P J Stevenson
- School of Chemistry and Chemical Engineering, Queen's University Belfast, Northern Ireland, United Kingdom
| | - A Panov
- School of Chemistry and Chemical Engineering, Queen's University Belfast, Northern Ireland, United Kingdom
| | - D Rodriguez-Lojo
- School of Chemistry and Chemical Engineering, Queen's University Belfast, Northern Ireland, United Kingdom
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Drużbicki K, Kocot A, Mikuli E, Ossowska-Chruściel MD, Chruściel J. Temperature-dependent infrared spectroscopy studies of a novel antiferroelectric liquid-crystalline thiobenzoate. J Phys Chem B 2012; 116:11332-43. [PMID: 22909143 DOI: 10.1021/jp305099v] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The temperature-dependent infrared spectroscopy studies of one novel antiferroelectric liquid crystal (AFLC), known under the MHPSBO10 acronym, have been undertaken. The FT-IR measurements have been performed for homeotropic and planar heterogeneous sample geometries. The main order parameters have been determined and followed with temperature. The presented study delivers complex insight into the evolution of the vibrational spectrum upon phase transitions, covering the whole mesophase range. The experimental studies have been supported by theoretical studies of MHPSBO10 in confined geometries.
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Affiliation(s)
- Kacper Drużbicki
- Department of Chemical Physics, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060, Cracow, Poland.
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Sanchez-Castillo A, Osipov MA, Jagiella S, Nguyen ZH, Kašpar M, Hamplovă V, Maclennan J, Giesselmann F. Orientational order parameters of a de Vries-type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:061703. [PMID: 23005110 DOI: 10.1103/physreve.85.061703] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Revised: 03/29/2012] [Indexed: 06/01/2023]
Abstract
The orientational order parameters (P{2}) and (P{4}) of the ferroelectric, de Vries-type liquid crystal 9HL have been determined in the SmA and SmC phases by means of polarized Raman spectroscopy, and in the SmA phase using x-ray diffraction. Quantum density functional theory predicts Raman spectra for 9HL that are in good agreement with the observations and indicates that the strong Raman band probed in the experiment corresponds to the uniaxial, coupled vibration of the three phenyl rings along the molecular long axis. The magnitudes of the orientational order parameters obtained in the Raman and x-ray experiments differ dramatically from each other, a discrepancy that is resolved by considering that the two techniques probe the orientational distributions of different molecular axes. We have developed a systematic procedure in which we calculate the angle between these axes and rescale the orientational order parameters obtained from x-ray scattering with results that are then in good agreement with the Raman data. At least in the case of 9HL, the results obtained by both techniques support a "sugar loaf" orientational distribution in the SmA phase with no qualitative difference to conventional smectics A. The role of individual molecular fragments in promoting de Vries-type behavior is considered.
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Affiliation(s)
- A Sanchez-Castillo
- Institut of Physical Chemistry, University of Stuttgart, Stuttgart, Germany
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Korlacki R, Panov VP, Fukuda A, Vij JK, Spillmann CM, Naciri J. Orientational order of a ferroelectric liquid crystal with small layer contraction. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:031702. [PMID: 21230086 DOI: 10.1103/physreve.82.031702] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Revised: 07/27/2010] [Indexed: 05/30/2023]
Abstract
We present spectroscopic and optical studies of a non-layer-shrinkage ferroelectric liquid crystal DSiKN65. The orientational order parameters S, measured with respect to the smectic layer normal using IR spectroscopy on a sample aligned homeotropically, does not exhibit any significant variation between the smectic-A∗ and smectic-C∗ phases. In contrast the birefringence of a planar homogenous sample abruptly increases at the smectic-A∗ to smectic-C∗ transition. This suggests a general increase in the orientational order, which can be described by the orientational order parameters S' defined with respect to the director. Simultaneous increase of S' and the director tilt Θ may explain the low shrinkage of smectic layers, which is consistent with recent theoretical models describing the smectic-A∗ to smectic-C∗ transition for such materials.
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Affiliation(s)
- Rafał Korlacki
- Department of Physics and Astronomy and The Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
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Korlacki R, Fukuda A, Vij JK, Kocot A, Görtz V, Hird M, Goodby JW. Self-assembly of biaxial ordering and molecular tilt angle of chiral smectic liquid crystals in homeotropically aligned cells investigated using infrared spectroscopy. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 72:041704. [PMID: 16383399 DOI: 10.1103/physreve.72.041704] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2005] [Revised: 04/21/2005] [Indexed: 05/05/2023]
Abstract
Temperature dependences of the infrared absorbance have been measured for the four chiral liquid crystal samples in the homeotropic cell configuration. It is shown that the values of the orientational order parameter obtained using this method exhibit a remarkable similarity to the x-ray diffraction results of the smectic layer spacing and lead to accurate values of the molecular tilt angle. This has important consequences for the existing interpretation of the x-ray data. The proposed method, in many cases, may be considered as a valuable alternative to the x-ray diffraction, giving additional, important information about the orientations and the ordering of the molecular fragments. It is found that if the experimentally obtained order parameter is low, then the molecular biaxiality is exceptionally large. The average phenyl ring plane is found to lie close to the molecular tilt plane.
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Affiliation(s)
- R Korlacki
- Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland
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Kang DS, Kwon KS, Kim SI, Gong MS, Seo SSA, Noh TW, Joo SW. Temperature-dependent Raman spectroscopic study of the nematic liquid crystal 4-n-pentyl-4'-cyanobiphenyl. APPLIED SPECTROSCOPY 2005; 59:1136-40. [PMID: 16197636 DOI: 10.1366/0003702055012492] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The spectral behaviors of 4-n-pentyl-4'-cyanobiphenyl (5 CB) have been studied by means of temperature-dependent Raman spectros-copy in the range between --70 and 70 degrees C. The nu(C identical with N) bands in the Raman spectra were found splitting below the transition temperature from the solid to the nematic liquid crystalline phase at approximately 24 degrees C, suggesting the existence of solid crystalline polymorphism. The interfacial structures of 5 CB on metal plate surfaces have been reexamined by surface-enhanced Raman scattering (SERS) at different temperatures. On Ag and Au, the asymmetric shapes of the nu(C identical with N) bands suggest that there should exist different binding schemes for 5 CB on metal surfaces. These asymmetric bands in the nu(C identical with N) stretching region were found to vary in changing temperature.
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Affiliation(s)
- Dae Seung Kang
- School of Electrical Engineering, Soongsil University, Seoul 156-743, Korea
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Hayashi N, Kato T, Fukuda A, Vij JK, Panarin YP, Naciri J, Shashidhar R, Kawada S, Kondoh S. Evidence for de Vries structure in a smectic-A liquid crystal observed by polarized Raman scattering. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:041705. [PMID: 15903689 DOI: 10.1103/physreve.71.041705] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2003] [Revised: 07/26/2004] [Indexed: 05/02/2023]
Abstract
The second- and fourth-order apparent orientational order parameters of the core part of the molecule P2 (app) and P4 (app) , have been measured by polarized vibrational Raman spectroscopy for a homogeneously aligned ferroelectric smectic liquid crystal with three dimethyl siloxane groups in the achiral terminal chain, which shows de Vries-type phenomena, i.e., very large electroclinic effect in the smectic- A (Sm-A) phase and a negligible layer contraction at the phase transition between the Sm-A and Sm- C(*) phases. The apparent orientational order parameters of the rigid core part of the molecule are extremely small both with and without the external electric field in Sm-A . These results provide evidence for the existence of the de Vries Sm-A phase, where the local molecular director is tilted at a large angle.
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Affiliation(s)
- Naoki Hayashi
- Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan.
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Hayashi N, Kato T, Aoki T, Ando T, Fukuda A, Seomun SS. Orientational distributions in smectic liquid crystals showing V-shaped switching investigated by polarized Raman scattering. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:041714. [PMID: 12005853 DOI: 10.1103/physreve.65.041714] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2001] [Indexed: 05/23/2023]
Abstract
Molecular orientational order parameters have been obtained by Raman scattering in two types of liquid crystal materials showing the V-shaped switching in thin homogeneous cells. One is the Mitsui mixture and the other is one component of the Inui mixture. The antiferroelectric phase exists in the bulk of both materials but, in thin homogeneous cells, the stability is distinct from each other. The obtained distribution of the local in-plane directors at the tip of the V is considerably broad in the former, while it is narrow in the latter. These differences have been explained by the barrier between the ferroelectric and antiferroelectric orderings, the chiral twisting power, and the interface induced destruction of the antiferroelectric ordering.
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Affiliation(s)
- Naoki Hayashi
- Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
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Hayashi N, Kato T, Aoki T, Ando T, Fukuda A, Seomun SS. Probable Langevin-like director reorientation in an interface-induced disordered SmC*-like state of liquid crystals characterized by frustration between ferro- and antiferroelectricity. PHYSICAL REVIEW LETTERS 2001; 87:015701. [PMID: 11461476 DOI: 10.1103/physrevlett.87.015701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2000] [Indexed: 05/23/2023]
Abstract
To clarify the thresholdless, hysteresis free V-shaped switching due to frustration between ferro- and antiferroelectricity, we have studied a prototype binary mixture system. The apparent orientational order parameters, <P2> and <P4>, obtained from polarized Raman scattering in thin homogeneous cells indicate that substrate interfaces induce some randomization of local in-plane directors at the tip of the V. Their correlation lengths, xi( parallel) approximately 3.5 nm and xi( perpendicular) approximately 75 nm, have been estimated by assuming the Langevin-like reorientation. Because of the much shorter xi(parallel) and xi(perpendicular) than the visible light wavelength, the switching process looks uniform.
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Affiliation(s)
- N Hayashi
- Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
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