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Ju J, Chatterjee D, Voyles PM, Bock H, Ediger MD. Vapor-to-glass preparation of biaxially aligned organic semiconductors. J Chem Phys 2023; 159:211101. [PMID: 38038197 DOI: 10.1063/5.0174819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2023] [Accepted: 11/02/2023] [Indexed: 12/02/2023] Open
Abstract
Physical vapor deposition (PVD) provides a route to prepare highly stable and anisotropic organic glasses that are utilized in multi-layer structures such as organic light-emitting devices. While previous work has demonstrated that anisotropic glasses with uniaxial symmetry can be prepared by PVD, here, we prepare biaxially aligned glasses in which molecular orientation has a preferred in-plane direction. With the collective effect of the surface equilibration mechanism and template growth on an aligned substrate, macroscopic biaxial alignment is achieved in depositions as much as 180 K below the clearing point TLC-iso (and 50 K below the glass transition temperature Tg) with single-component disk-like (phenanthroperylene ester) and rod-like (itraconazole) mesogens. The preparation of biaxially aligned organic semiconductors adds a new dimension of structural control for vapor-deposited glasses and may enable polarized emission and in-plane control of charge mobility.
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Affiliation(s)
- Jianzhu Ju
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Debaditya Chatterjee
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Paul M Voyles
- Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - Harald Bock
- Centre de Recherche Paul Pascal, CNRS & Université de Bordeaux, 33600 Pessac, France
| | - Mark D Ediger
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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2
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Molecular dynamics of alkyl benzoate liquid crystals in the bulk state and in the surface layer of their composites with oxide nanopowders. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.119374] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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3
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Wang H, Kearns KL, Zhang A, Arabi Shamsabadi A, Jin Y, Bond A, Hurney SM, Morillo C, Fakhraai Z. Effect of Nanopore Geometry in the Conformation and Vibrational Dynamics of a Highly Confined Molecular Glass. NANO LETTERS 2021; 21:1778-1784. [PMID: 33555892 DOI: 10.1021/acs.nanolett.0c04744] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The effect of nanoporous confinement on the glass transition temperature (Tg) strongly depends on the type of porous media. Here, we study the molecular origins of this effect in a molecular glass, N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), highly confined in concave and convex geometries. When confined in controlled pore glass (CPG) with convex pores, TPD's vibrational spectra remained unchanged and two Tg's were observed, consistent with previous studies. In contrast, when confined in silica nanoparticle packings with concave pores, the vibrational peaks were shifted due to more planar conformations and Tg increased, as the pore size was decreased. The strong Tg increases in concave pores indicate significantly slower relaxation dynamics compared to CPG. Given TPD's weak interaction with silica, these effects are entropic in nature and are due to conformational changes at molecular level. The results highlight the role of intramolecular degrees of freedom in the glass transition, which have not been extensively explored.
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Affiliation(s)
- Haonan Wang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Kenneth L Kearns
- Department of Chemistry, Saginaw Valley State University, University Center, Michigan 48710, United States
| | - Aixi Zhang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Ahmad Arabi Shamsabadi
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Yi Jin
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Aaron Bond
- Department of Chemistry, Saginaw Valley State University, University Center, Michigan 48710, United States
| | - Steven M Hurney
- Department of Chemistry, Saginaw Valley State University, University Center, Michigan 48710, United States
| | - Carlos Morillo
- JASCO Incorporated, Easton, Maryland 21601, United States
| | - Zahra Fakhraai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
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Yamaguchi T, Nut Leelaphattharaphan N, Shin H, Ogawa M. Acceleration of photochromism and negative photochromism by the interactions with mesoporous silicas. Photochem Photobiol Sci 2019; 18:1742-1749. [PMID: 31093626 DOI: 10.1039/c9pp00081j] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The adsorption of merocyanine dye onto mesoporous silicas with varied pore sizes (5.5, 9.4 and 2.2 nm) from the toluene solution of 1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran under UV irradiation was investigated quantitatively. The photoinduced adsorption of merocyanine onto SBA-15 with the pore diameter of 9.4 nm followed the pseudo-second order kinetics and the rate constant was larger than that observed for MCM-41 (pore size of 2.2 nm) owing to the efficient diffusion of merocyanine. The maximum adsorbed amounts of the merocyanine dye was 152 mg g-1 of SBA-15, which corresponded to the sufficiently high concentration of merocyanine in the pores (0.376 mol L-1 of pore). The resulting red-colored hybrids (SBA-15 containing merocyanine) showed decoloration in the solid-state by visible light irradiation (negative photochromism). The conversion was high (about 80% at the photostationary state) under visible light irradiation at room temperature using a solar simulator (100 W). The red color was re-generated by storing the photochemically formed colorless samples in the dark at room temperature. The half-lives of the thermal coloration process were 2.6, 1.9 and 1.3 h for the MCM-41, SBA-15s with the BJH pore sizes of 5.5 and 9.4 nm, respectively. Since the coloration was affected by the diffusion of the molecules in the pores, larger pores provided the efficient molecular diffusion, leading to faster reactions.
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Affiliation(s)
- Tetsuo Yamaguchi
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| | - Nattapat Nut Leelaphattharaphan
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| | - Hojoon Shin
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| | - Makoto Ogawa
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
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Structural and thermotropic peculiarities of hydrogen-bonded liquid crystals confined in mesoporous molecular sieves. J Mol Struct 2016. [DOI: 10.1016/j.molstruc.2016.04.064] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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6
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Affiliation(s)
- R. Richert
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604;
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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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8
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Yashonath S, Ghorai PK. Diffusion in Nanoporous Phases: Size Dependence and Levitation Effect. J Phys Chem B 2007; 112:665-86. [DOI: 10.1021/jp076031z] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- S. Yashonath
- Solid State and Structural Chemistry Unit, Center for Condensed Matter Theory, Indian Institute of Science, Bangalore-560012, India
| | - Pradip Kr. Ghorai
- Solid State and Structural Chemistry Unit, Center for Condensed Matter Theory, Indian Institute of Science, Bangalore-560012, India
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Vilfan M, Apih T, Sebastião PJ, Lahajnar G, Zumer S. Liquid crystal 8CB in random porous glass: NMR relaxometry study of molecular diffusion and director fluctuations. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:051708. [PMID: 18233674 DOI: 10.1103/physreve.76.051708] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Indexed: 05/25/2023]
Abstract
We present the measurements of the proton spin-lattice relaxation time T1 of liquid crystal 4-n-octyl-4'-cyanobiphenyl (8CB) confined into randomly oriented approximately 15 nm pores of untreated porous glass. In the low kilohertz range the spin-lattice relaxation rate in the nanoconfined 8CB is about ten times larger than in the bulk. We show that the increase is mainly due to molecular reorientations mediated by translational displacements (RMTD). In the paranematic phase the power law describing the RMTD dispersion, (T1(-1))RMTD proportional, omega(-p), is well characterized by the exponent p=0.5+/-0.06 and suggests an equipartition of diffusion modes with different wavelengths. The largest distance related to the decay of the orientational correlation function is about twice the diameter of the cavity. The situation is different in the nematic phase, where the orientational correlation is eventually lost at approximately 60 nm in the direction along the pore, a distance corresponding roughly to the length of a pore segment in the glassy matrix. The exponent p is between 0.65 and 0.9, depending on the temperature, which implies that in the nematic phase long wavelength modes are relatively more important--a consequence of the uniform director field along the pore. These observations are in agreement with the model of mutually independent pores with nematic director parallel to the pore axis in each segment. We point out that in strongly confined liquid crystals the proton NMR relaxometry does not provide the evidence of director fluctuations correlated over micrometer distances as was suggested earlier. The local translational diffusion of molecules within the cavities is found about as fast as in bulk.
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Affiliation(s)
- M Vilfan
- Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
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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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11
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Rozanski SA, Naji L, Kremer F, Stannarius R. Influence of Confining Geometries on Collective Dynamic Modes in Chiral Smectogens. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259908025972] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- S. A. Rozanski
- a Maria Sklodowska-Curie High School , W. Pola 11, 64‐920 , Pila , Poland
| | - L. Naji
- b Universität Leipzig, Fakultät für Physik und Geowissenschaften , Linnéstr. 5, D-04103 , Leipzig , Germany
| | - F. Kremer
- b Universität Leipzig, Fakultät für Physik und Geowissenschaften , Linnéstr. 5, D-04103 , Leipzig , Germany
| | - R. Stannarius
- b Universität Leipzig, Fakultät für Physik und Geowissenschaften , Linnéstr. 5, D-04103 , Leipzig , Germany
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Swenson J, Engberg D, Howells WS, Seydel T, Juranyi F. Dynamics of propylene glycol and its oligomers confined to a single molecular layer. J Chem Phys 2005; 122:244702. [PMID: 16035788 DOI: 10.1063/1.1943408] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The dynamics of propylene glycol (PG) and its oligomers 7-PG and poly-propylene glycol (PPG), with M(w) = 4000 (approximately 70 monomers), confined in a Na-vermiculite clay have been investigated by quasielastic neutron scattering. The liquids are confined to single molecular layers between clay platelets, giving a true two-dimensional liquid. Data from three different spectrometers of different resolutions were Fourier transformed to S(Q,t) and combined to give an extended dynamical time range of 0.3-2000 ps. An attempt was made to distinguish the diffusive motion from the methyl group rotation and a fast local motion of hydrogen in the polymer backbone. The results show that the average relaxation time tau(d) of this diffusive process is, as expected, larger than the relaxation time tau averaged over all dynamical processes observed in the experimental time window. More interesting, it is evident that the severe confinement has a relatively small effect on tau(d) at T = 300 K, this holds particularly for the longest oligomer, PPG. The most significant difference is that the chain-length dependence of tau(d) is weaker for the confined liquids, although the slowing down in bulk PG due to the formation of a three-dimensional network of OH-bonded end groups reduces this difference. The estimated average relaxation time tau at Q = 0.92 Angstroms(-1) for all the observed processes is in excellent agreement with the previously reported dielectric alpha relaxation time in the studied temperature range of 260-380 K. The average relaxation time tau (as well as the dielectric alpha relaxation time) is also almost unaffected by the confinement to a single molecular layer, suggesting that the interaction with the clay surfaces is weak and that the reduced dimensionality has only a weak influence on the time scale of all the dynamical processes observed in this study.
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Affiliation(s)
- J Swenson
- Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
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Baumann R, Ferrante C, Kneuper E, Deeg FW, Bräuchle C. Influence of Confinement on the Solvation and Rotational Dynamics of Coumarin 153 in Ethanol. J Phys Chem A 2003. [DOI: 10.1021/jp027172y] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert Baumann
- Department Chemie, Bereich Physikalische Chemie, Ludwig-Maximilians- Universität, Butenandtstrasse 5-13, D-81377 München, Germany
| | - Camilla Ferrante
- Department Chemie, Bereich Physikalische Chemie, Ludwig-Maximilians- Universität, Butenandtstrasse 5-13, D-81377 München, Germany
| | - Erwin Kneuper
- Department Chemie, Bereich Physikalische Chemie, Ludwig-Maximilians- Universität, Butenandtstrasse 5-13, D-81377 München, Germany
| | - Fred-Walter Deeg
- Department Chemie, Bereich Physikalische Chemie, Ludwig-Maximilians- Universität, Butenandtstrasse 5-13, D-81377 München, Germany
| | - Christoph Bräuchle
- Department Chemie, Bereich Physikalische Chemie, Ludwig-Maximilians- Universität, Butenandtstrasse 5-13, D-81377 München, Germany
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14
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Swenson J, Howells WS. Quasielastic neutron scattering of propylene glycol and its 7-mer confined in clay. J Chem Phys 2002. [DOI: 10.1063/1.1483071] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Roussel F, Canlet C, Fung BM. Morphology and orientational order of nematic liquid crystal droplets confined in a polymer matrix. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:021701. [PMID: 11863539 DOI: 10.1103/physreve.65.021701] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2001] [Indexed: 05/23/2023]
Abstract
The orientational order of nematic liquid crystal (LC) droplets confined in a polymer matrix is investigated by 13C-NMR. Different morphologies exhibiting various cavity sizes were obtained by changing the LC fraction. The phase diagram has been established by polarized optical microscopy exhibiting a typical upper critical solution temperature shape. The nematic order increases with decreasing droplet size which may result from increased polymer/LC surface contacts in smaller cavities. The nematic fraction of 4-n-pentyl-4'-cyanobiphenyl (5CB) contained in the droplets was calculated by integrating the NMR peaks, then fitted using a simple theoretical model and compared with differential scanning calorimetry results. NMR investigations in the aliphatic region of the spectra have shown that the 2-ethyl hexyl fragment of the polymer chain is partially ordered at the polymer/LC interface due to interdigitation with 5CB molecules. Above the nematic-isotropic transition temperature, a weak pretransitional behavior is shown by the polymer.
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Affiliation(s)
- Frédérick Roussel
- Laboratoire de Thermophysique de la Matière Condensée, Equipe de l'UPRESA CNRS 8024, Université du Littoral-Côte d'Opale, MREID, 59140 Dunkerque, France.
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Bayer A, Kopitzke J, Noll F, Seifert A, Wendorff JH. Polymer Dispersed Discotics: Structure, Dynamics, and Optoelectronic Properties. Macromolecules 2001. [DOI: 10.1021/ma001470g] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A. Bayer
- Department of Chemistry and Materials Science Center, Philipps University, Marburg, Germany
| | - J. Kopitzke
- Department of Chemistry and Materials Science Center, Philipps University, Marburg, Germany
| | - F. Noll
- Department of Chemistry and Materials Science Center, Philipps University, Marburg, Germany
| | - A. Seifert
- Department of Chemistry and Materials Science Center, Philipps University, Marburg, Germany
| | - J. H. Wendorff
- Department of Chemistry and Materials Science Center, Philipps University, Marburg, Germany
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17
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Baumann R, Ferrante C, Deeg FW, Bräuchle C. Solvation dynamics of nile blue in ethanol confined in porous sol–gel glasses. J Chem Phys 2001. [DOI: 10.1063/1.1309151] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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18
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Vilfan M, Apih T, Gregorovic A, Zalar B, Lahajnar G, Zumer S, Hinze G, Böhmer R, Althoff G. Surface-induced order and diffusion in 5CB liquid crystal confined to porous glass. Magn Reson Imaging 2001; 19:433-8. [PMID: 11445325 DOI: 10.1016/s0730-725x(01)00262-4] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Liquid crystals confined into small cavities are known to have a weak orientational order even above the nematic-isotropic transition temperature. The surface-induced order and molecular dynamics in this temperature range are studied with the aid of deuteron NMR spectra, spin relaxation times T(1) and T(2,) proton dipolar-correlation effect, and direct measurements of the effective diffusion coefficient for the liquid crystal 5CB confined to controlled-pore glasses. Our results show that an arrangement of molecules parallel to the wall is induced by local molecular interactions between the liquid crystal and solid, resulting in a weak and temperature independent surface order parameter, S(0) approximately 0.02 +/- 0.01. There is no indication of a significant slowing-down of molecular diffusion at the wall, neither rotational nor translational. In cavities of nanometer size, where the nematic order evolves gradually upon cooling, a broadening of the NMR linewidths due to dynamic effects should be taken into account.
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Affiliation(s)
- M Vilfan
- J. Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia.
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Loughnane BJ, Farrer RA, Scodinu A, Fourkas JT. Dynamics of a wetting liquid in nanopores: An optical Kerr effect study of the dynamics of acetonitrile confined in sol-gel glasses. J Chem Phys 1999. [DOI: 10.1063/1.479768] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Sarlah A, Zumer S. Equilibrium structures and pretransitional fluctuations in a very thin hybrid nematic film. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:1821-30. [PMID: 11969969 DOI: 10.1103/physreve.60.1821] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/1999] [Revised: 04/16/1999] [Indexed: 04/18/2023]
Abstract
The stability of different structures of a nematic liquid crystal in a planar hybrid film is examined within the framework of a Gaussian description of order fluctuations. In a very thin film the director field is not bent smoothly but exhibits a steplike change if the anchorings at the confining substrates are strong (G approximately > or =10(-3) J/m(2)) and comparable in magnitude. A (dis)continuous structural transition to the bent-director state which occurs with increasing film thickness or decreasing temperature is governed by the lowest bending director fluctuation mode. Its relaxation rate exhibits a critical slowdown when the film thickness approaches the "supercooling" limit or transition point, respectively. The (dis)continuity of the structural transition depends on the temperature and film thickness. The upper limit for the corresponding tricritical point is determined. The lowest order parameter mode, which corresponds to fluctuations of the position of the central exchange region, is characterized by a nearly critical behavior of the relaxation rate. The spectra of the two noncritical biaxial fluctuation modes are degenerate, whereas the fluctuation profiles are just mirror images with respect to the middle plane of the film.
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Affiliation(s)
- A Sarlah
- Department of Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
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Frunza S, Frunza L, Schoenhals A, Zubowa HL, Kosslick H, Carius HE, Fricke R. On the confinement of liquid crystals in molecular sieves: dielectric measurements. Chem Phys Lett 1999. [DOI: 10.1016/s0009-2614(99)00523-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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23
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Schönhals A, Stauga R. Broadband dielectric study of anomalous diffusion in a poly(propylene glycol) melt confined to nanopores. J Chem Phys 1998. [DOI: 10.1063/1.475918] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Huwe A, Arndt M, Kremer F, Haggenmüller C, Behrens P. Dielectric investigations of the molecular dynamics of propanediol in mesoporous silica materials. J Chem Phys 1997. [DOI: 10.1063/1.475265] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Cramer C, Cramer T, Kremer F, Stannarius R. Measurement of orientational order and mobility of a nematic liquid crystal in random nanometer confinement. J Chem Phys 1997. [DOI: 10.1063/1.473425] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Arndt M, Stannarius R, Gorbatschow W, Kremer F. Dielectric investigations of the dynamic glass transition in nanopores. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:5377-5390. [PMID: 9965723 DOI: 10.1103/physreve.54.5377] [Citation(s) in RCA: 198] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Stallinga S, Wittebrood MM, Luijendijk DH, Rasing T. Theory of light scattering by thin nematic liquid crystal films. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:6085-6092. [PMID: 9964969 DOI: 10.1103/physreve.53.6085] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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28
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Bhattacharya A, Rao M, Chakrabarti A. Kinetics of phase ordering of nematic liquid crystals in a confined geometry. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:4899-4903. [PMID: 9964818 DOI: 10.1103/physreve.53.4899] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Kralj S, Zidansek A, Lahajnar G, Musevic I, Zumer S, Blinc R, Pintar MM. Nematic ordering in porous glasses: A deuterium NMR study. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:3629-3638. [PMID: 9964673 DOI: 10.1103/physreve.53.3629] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Streck C, Mel'nichenko YB, Richert R. Dynamics of solvation in supercooled liquids confined to the pores of sol-gel glasses. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 53:5341-5347. [PMID: 9984139 DOI: 10.1103/physrevb.53.5341] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Iannacchione GS, Crawford GP, Qian S, Doane JW, Finotello D, Zumer S. Nematic ordering in highly restrictive Vycor glass. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:2402-2411. [PMID: 9964525 DOI: 10.1103/physreve.53.2402] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Grinberg F, Kimmich R, Stapf S. Investigation of molecular order and dynamics in liquid crystals confined in porous media using the dipolar-correlation effect on the stimulated echo. Magn Reson Imaging 1996; 14:883-5. [PMID: 8970100 DOI: 10.1016/s0730-725x(96)00172-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A new application of the stimulated echo pulse sequence is presented that permits the elucidation of molecular order and dynamics in a time scale between about 100 microseconds and the spin-lattice relaxation time. The technique exploits the influence of dipolar coupling on the quotient of the stimulated and primary echoes produced by the standard three 90 degrees-pulse sequence. Results obtained for a nematic liquid crystal in bulk and confined in porous glass (mean pore diameter 4 nm) are compared. In both cases the echo amplitude quotient oscillates as a function of the pulse spacing. In a bulk nematic crystal these oscillations originate from strong unaveraged dipolar interactions and directly reflect the molecular order in the material. In porous glass a real nematic order is absent. In this case, the oscillations can be attributed to spin exchange between inequivalent protons. Exchange rates are estimated.
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Affiliation(s)
- F Grinberg
- Universität Ulm, Sektion Kernresonanzspektroskopie, Germany
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Zhang Z, Chakrabarti A. Nematic ordering in a Vycor-like restrictive geometry: A two-dimensional model. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1995; 52:4991-4999. [PMID: 9963994 DOI: 10.1103/physreve.52.4991] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Renner C, Löwen H, Barrat JL. Orientational glass transition in a rotator model. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1995; 52:5091-5099. [PMID: 9964006 DOI: 10.1103/physreve.52.5091] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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