The Influence of Boundary Conditions and Surface Layer Thickness on Dielectric Relaxation of Liquid Crystals Confined in Cylindrical Pores

2000 ◽  
Vol 651 ◽  
Author(s):  
Z. Nazario ◽  
G. P. Sinha ◽  
F.M. Aliev
Keyword(s):  
Liquid Crystal ◽  
Boundary Conditions ◽  
Temperature Dependence ◽  
Layer Thickness ◽  
Dielectric Spectroscopy ◽  
Relaxation Times ◽  
Thin Layers ◽  
Short Axis ◽  
Librational Mode ◽  
Cylindrical Pores

AbstractDielectric spectroscopy was applied to investigate the dynamic properties of liquid crystal octylcyanobiphenyl (8CB) confined in 2000 Å cylindrical pores of Anopore membranes with homeotropic and axial (planar) boundary conditions on the pore walls. Homeotropic boundary conditions allow the investigation of the librational mode in 8CB by dielectric spectroscopy. We found that the dynamics of the librational mode is totally different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependence of relaxation times and of the dielectric strength of the librational mode needs the involvement of the temperature dependence of orientational order parameter. For samples with axial boundary conditions, layers of LCs with different thickness were obtained on the pore walls as a result of controlled impregnation of porous matrices with 8CB from solutions of different liquid crystal concentration. The process due to rotation of molecules around their short axis with single relaxation time observed for bulk 8CB is replaced by a process with a distribution of relaxation times in thin layers. This relaxation process broadens with decreasing layer thickness.

Influence of Confinement on Molecular Reorientational Dynamics of Liquid Crystals: Broadband Dielectric Spectroscopy Investigations

2001 ◽  
Vol 699 ◽  
Author(s):  
Fouad M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Dielectric Spectroscopy ◽  
Orientational Order ◽  
Relaxation Times ◽  
Thin Layers ◽  
Short Axis ◽  
Cylindrical Pore ◽  
Broadband Dielectric Spectroscopy ◽  
Librational Mode ◽  
Cylindrical Pores

AbstractBroadband dielectric spectroscopy has been applied for investigations of the dynamic behavior of liquid crystals (LCs) confined in porous matrices with random pores as well as in parallel cylindrical pores. We observed deep supercooling of LC in random pores. The relaxation times of the process due to the molecular rotation in deeply supercooled state are slower than at the temperatures corresponding to nematic phase by a factor of 106. This slowing down is accompanied by anomalous broadening of the dielectric spectra. For LC confined in cylindrical pores with homeotropic orientation on the pore walls we have investigated the relaxation of the librational mode. The dynamics of this mode is different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. The interpretation of the temperature dependencies of relaxation times of the librational mode needs the involvement of the temperature dependence of orientational order parameter. The investigations of the relaxation in thin LC layers formed on cylindrical pore walls show that the process due to rotation of molecules around their short axis (with single relaxation time for bulk LC) is the process with a distribution of relaxation times in thin layers and this process broadens with decreasing thickness of the layers.

Collective and Molecular Dielectric Relaxation in Confined Liquid Crystals: Effect of Different Layer Thicknesses and Boundary Conditions

2003 ◽  
Vol 790 ◽  
Author(s):  
Fouad M. Aliev ◽  
Manuel Rivera Bengoechea
Keyword(s):  
Liquid Crystal ◽  
Boundary Conditions ◽  
Layer Thickness ◽  
High Frequency ◽  
Low Frequency ◽  
Pore Wall ◽  
Relaxation Processes ◽  
Short Axis ◽  
Librational Mode ◽  
Frequency Relaxation

ABSTRACTBroadband dielectric spectroscopy was used to study the influence of boundary conditions and layer thickness of liquid crystal (LC) confined to cylindrical pores on low frequency and high frequency relaxation processes. Low frequency measurements provided information on the relaxation of surface polarization that arose at LC – pore wall interface. The dynamics of molecular reorientations were investigated in high frequency experiments. In samples with axial orientation of molecules, the dielectric mode due to reorientation of molecules around their short axis was investigated. The homeotropic alignment of molecules facilitated the investigation of the librational mode. The behavior of this mode was different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. Broadening of the dielectric spectra was observed in confined LC. The broadening increases with decreasing liquid crystal layer thickness.

scholarly journals The Dynamic Properties of 5Cb Filled with Aerosil Particles Investigated by Pcs

1999 ◽  
Vol 559 ◽  
Author(s):  
F.M. Aliev ◽  
M. Kreuzer ◽  
Yu.P. Panarin
Keyword(s):  
Liquid Crystal ◽  
Temperature Dependence ◽  
Relaxation Process ◽  
Nematic Liquid Crystal ◽  
Broad Spectrum ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Correlation Spectroscopy ◽  
Relaxation Processes ◽  
Optoelectronic Application

ABSTRACTNematic liquid crystal filled with Aerosil particles, a prospective composite material for optoelectronic application, has been investigated by static light scattering and Photon Correlation Spectroscopy (PCS). The Aerosil particles in filled nematic liquid crystals (FN) form a network structure with LC domains about 2500 Å in size with a random distribution of the director orientation of each domain.We found that the properties of 5CB are considerably affected by the network. The N-I phase transition in filled 5CB was found to be smeared out and depressed. PCS experiments show that two new relaxation processes appear in filled 5CB in addition to the director fluctuation process in bulk. The slow relaxation process, with a broad spectrum of relaxation times, is somewhat similar to the slow decay, which is observed in confined nematic liquid crystal.The middle frequency process was assigned to the director fluctuations in the surface layer formed at the particle-LC interface. The decay function describing this relaxation process is a stretched exponential (β ≍ 0.7). The temperature dependence of the relaxation times of the middle frequency obeys the Vogel-Rilcher law. Such a temperature dependence, accompanied by a broad spectrum of relaxation times suggests that the dynamics of the director fluctuations near the Aerosil particle-LC interface is glass-like.

Broad-Band Dielectric Spectroscopy of Liquid Crystals Confined in Random and Cylindrical Pores

1996 ◽  
Vol 464 ◽  
Author(s):  
G.P. Sinha ◽  
F.M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Dielectric Spectroscopy ◽  
Dynamic Properties ◽  
Nematic Liquid Crystals ◽  
Broad Band ◽  
Low Frequency ◽  
Molecular Rotation ◽  
Retardation Factor ◽  
Short Axis ◽  
Cylindrical Pores

ABSTRACTUsing dielectric spectroscopy in the frequency range 0.1 Hz-1.5 GHz, we investigated the influence of confinement on the dynamic properties of polar nematic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different, pores sizes. The confinement has a strong influence on the dielectric properties of LC which resulted in the appearance of a low frequency relaxational process (f ≤ 10 KHz) absent in bulk and a strong modification of modes due to the molecular rotation around short axis and librational motion. The differences between bulk and confined behavior are: (a) - the dielectrically active modes in confined LC are not frozen even at temperatures about 20 degrees below the bulk crystallization temperature; (b) - in the temperature range corresponding to the anisotropie phase in pores, lnτ, where τ is the relaxation time corresponding to the molecular rotation around short axis, is not a linear function of 1/T and there is an evidence for smectic type order formation at sufficiently low T; (c) - the retardation factor g = τ/τis is ≃ 1.5, where as the typical value of g in bulk nematic liquid crystals is ≃ 4; (d) - smooth and small changes in T at phase transition in pores suggest that the “isotropie” phase of LC in pores is not bulk like isotropie phase with complete disorder in molecular orientations, and some degree of orientation order still persists.

Molecular Reorientation in Solid Chlorine

1973 ◽  
Vol 51 (21) ◽  
pp. 2300-2305 ◽  
Author(s):  
R. T. Obermyer ◽  
E. P. Jones
Keyword(s):  
Temperature Dependence ◽  
Nuclear Quadrupole Resonance ◽  
Raman Spectra ◽  
Relaxation Times ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Librational Mode ◽  
Resonance Frequencies ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole

Nuclear quadrupole resonance frequencies and relaxation times of 35Cl and 37Cl in solid chlorine have been measured from 4.2 °K to near the melting point. An analysis of the temperature dependence of the nuclear quadrupole resonance frequencies was made using values for three librational mode frequencies determined previously from Raman spectra. The frequency of a fourth mode was predicted from this analysis. The spin–lattice relaxation times were analyzed using the Bayer model extended by Woessner and Gutowsky and using the librational mode frequencies determined from Raman spectra and the temperature dependence of the nuclear quadrupole resonance frequencies.

Dielectric Relaxation Studies of Silver Nanoparticles dispersed Liquid Crystal

2015 ◽  
Vol 8 (3) ◽  
pp. 2176-2188 ◽  
Author(s):  
Keisham Nanao Singh
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Liquid Crystal ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Relaxation Times ◽  
Low Frequency ◽  
Bulk Liquid ◽  
Molecular Rearrangement ◽  
Relaxation Studies

This article reports on the Dielectric Relaxation Studies of two Liquid Crystalline compounds - 7O.4 and 7O.6 - doped with dodecanethiol capped Silver Nanoparticles. The liquid crystal molecules are aligned homeotropically using CTAB. The low frequency relaxation process occurring above 1 MHz is fitted to Cole-Cole formula using the software Dielectric Spectra fit. The effect of the Silver Nanoparticles on the molecular dipole dynamics are discussed in terms of the fitted relaxation times, Cole-Cole distribution parameter and activation energy. The study indicate a local molecular rearrangement of the liquid crystal molecules without affecting the order of the bulk liquid crystal molecules but these local molecules surrounding the Silver Nanoparticles do not contribute to the relaxation process in the studied frequency range. The observed effect on activation energy suggests a change in interaction between the nanoparticles/liquid crystal molecules.

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