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.

Temperature Dependence of Dynamic Properties of Elastomers. Relaxation Distributions

1952 ◽  
Vol 25 (4) ◽  
pp. 720-729 ◽  
Author(s):  
John D. Ferry ◽  
Edwin R. Fitzgerald ◽  
Lester D. Grandine ◽  
Malcolm L. Williams
Keyword(s):  
Distribution Function ◽  
Temperature Dependence ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Dynamic Mechanical Properties ◽  
Relaxation Processes ◽  
The Real ◽  
Reduced Frequency ◽  
Dynamic Rigidity ◽  
Composite Curve

Abstract By the use of reduced variables, the temperature dependence and frequency dependence of dynamic mechanical properties of rubberlike materials can be interrelated without any arbitrary assumptions about the functional form of either The definitions of the reduced variables are based on some simple assumptions regarding the nature of relaxation processes. The real part of the reduced dynamic rigidity, plotted against the reduced frequency, gives a single composite curve for data over wide ranges of frequency and temperature; this is true also for the imaginary part of the rigidity or the dynamic viscosity. The real and imaginary parts of the rigidity, although independent measurements, are interrelated through the distribution function of relaxation times, and this relation provides a check on experimental results. First and second approximation methods of calculating the distribution function from dynamic data are given. The use of the distribution function to predict various types of time-dependent mechanical behavior is illustrated.

Nanocomposite Material, Liquid Crystal-Aerosil Particles: Dielectric and Photon Correlation Spectroscopy Investigations

1999 ◽  
Vol 581 ◽  
Author(s):  
F.M. Aliev ◽  
G.P. Sinha
Keyword(s):  
Liquid Crystal ◽  
Photon Correlation Spectroscopy ◽  
Low Frequency ◽  
Correlation Spectroscopy ◽  
Relaxation Processes ◽  
Photon Correlation ◽  
Optoelectronic Application ◽  
Broadband Dielectric Spectroscopy ◽  
Tumbling Motion ◽  
Frequency Relaxation

ABSTRACTNematic liquid crystal filled with Aerosil particles prospective inorganic-organic nanocom-posite material for optoelectronic application has been investigated by broadband dielectric spectroscopy (BDS) and photon correlation spectroscopy (PCS). The aerosil particles of diameter ≈ 10 nm in filled nematic liquid crystals form a network structure with linear size of LC domains about 250 nm and with random distribution of the director orientation of each domain. This material has a very developed liquid crystal-solid particle interface that makes the role of the surface layers of LC important in the determination of the properties of the material. BDS provides information on reorientational motion of polar molecules of liquid crystal while PCS probes dynamics of collective modes associated with director fluctuations. We found that the properties of 5CB are considerably affected by the network. Two bulk-like dielectric modes due to the rotation of molecules around short axes and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and dispersion of dielectric permittivity due to conductivity were observed. The treatment of the surface of filling particles has strongest influence on the properties of the slow process and it is less important for molecular modes. PCS experiment shows that two new relaxation processes appear in filled 5CB in addition to the director fluctuations process in bulk.

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.

Polar Anchoring Strength and the Temperature Dependence of Nematic Liquid Crystal (5CB) Aligned on Rubbed Polystyrene Films

1992 ◽  
Vol 31 (Part 1, No. 7) ◽  
pp. 2165-2169 ◽  
Author(s):  
Dae-Shik Seo ◽  
Koh-ichi Muroi ◽  
Toh-ru Isogami ◽  
Hideaki Matsuda ◽  
Shunsuke Kobayashi
Keyword(s):  
Liquid Crystal ◽  
Temperature Dependence ◽  
Nematic Liquid Crystal ◽  
Anchoring Strength ◽  
Liquid Crystal 5Cb

Determination of Temperature Dependence of Kerr Constant for Nematic Liquid Crystal

2011 ◽  
Vol 544 (1) ◽  
pp. 227/[1215]-231/[1219] ◽  
Author(s):  
M. H. Majles Ara ◽  
S. H. Mousavi ◽  
M. Rafiee ◽  
M. S. Zakerhamidi
Keyword(s):  
Liquid Crystal ◽  
Temperature Dependence ◽  
Nematic Liquid Crystal ◽  
Kerr Constant

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.

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