Slow Dynamics and Glass-Like Behavior of Liquid Crystals Dispersed in Nanoporous Media

1996 ◽  
Vol 455 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Liquid Crystals ◽  
Relaxation Times ◽  
Time Range ◽  
Slow Mode ◽  
Photon Correlation ◽  
Nanoporous Media ◽  
Cylindrical Pores ◽  
Relaxational Process ◽  
Porous Matrices ◽  
Interconnected Pores

ABSTRACTWe have investigated the dynamic behavior of liquid crystals (LC), which are not glass formers when in bulk form, confined in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different pore sizes by photon correlation (time range: 20 ns-103s) and dielectric spectroscopies (frequencies: 0.1 Hz-1.5GHz). We observed that in random pores (pore size is 10 nm and 100 nm) LC does not crystallize at temperatures about 25° C below bulk crystallization temperature and the non-Debye relaxational processes studied by both photon correlation and dielectric experiments were found not to be frozen. Slow relaxational process which does not exist in bulk LC and a broad spectrum of relaxation times (10−8 − 10)s appear not only for LC in random pores but in cylindrical pores as well. However in matrices with random pores of 100 Å, glass-like behavior of slow mode (τ > 1ms) was observed. The relaxation time (determined in photon correlation experiment) of this slow process strongly increases when temperature decreases from 300 K up to 270 K varying from 0.2ms to 14 s and it's temperature dependence is described by the Vogel-Fulcher law.

Heterogeneous Microcomposite Materials Based on Porous Matrices and Liquid Crystals

1996 ◽  
Vol 431 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Liquid Crystals ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Physical Properties ◽  
Wide Spectrum ◽  
Relaxation Times ◽  
Average Pore ◽  
Relaxational Process ◽  
Porous Matrices ◽  
Interconnected Pores

AbstractHeterogeneous microcomposite materials based on porous matrices with randomly oriented, interconnected pores (porous glasses with average pore sizes of 100 Å and 1000 Å) and parallel cylindrical pores (Anopore membranes with pore diameters of 200 Å and 2000 Å) impregnated with liquid crystals (LC) were investigated by dynamic light scattering and dielectric spectroscopy. The physical properties of confined LC are very different from that of the bulk. One of the new properties among others observed for LC confined in porous matrices is the slow relaxational process which does not exist in the bulk LC and a wide spectrum of relaxation times (10−8 – 10)s which were established in both dynamic light scattering and dielectric experiments. We found that for LC dispersed in porous matrices with randomly distributed interconnected pores, the contribution to physical properties and observed behavior from interfacial layers dominates and almost completely determines low frequency relaxational process.

Photon Correlation Spectroscopy of Liquid Crystals Confined in Porous Matrices with Different Structure and Pore Size

1996 ◽  
Vol 464 ◽  
Author(s):  
F.M. Aliev ◽  
I.V. Plechakov
Keyword(s):  
Liquid Crystals ◽  
Pore Size ◽  
Photon Correlation Spectroscopy ◽  
Dynamical Behavior ◽  
Correlation Spectroscopy ◽  
Finite Size Effect ◽  
Random Structure ◽  
Photon Correlation ◽  
Cylindrical Pores ◽  
Porous Matrices

ABSTRACTWe present the results of photon correlation spectroscopy investigations of the influence of confinement, interface, porous matrix structure, pore size and shape on the dynamic behavior of nematic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores (porous glasses) and parallel cylindrical pores (Anopore membranes). Investigations of LC in cylindrical pores together with studies in random porous matrices, makes it possible to separate the role of random structure and domain formation from the contributions due to existence of LC - solid pore wall interface and pure finite size effect in relaxation of order parameter or director fluctuations. In the temperature range below nematic - isotropie phase transition temperature we observed two overlapping relaxational processes which are satisfactorily described by the decay function f(q,t) = a·exp(–t/τ1) + (1–a)·exp(–xz), where x = ln(t/τ0)/ln(τ2/τ0) and τ0 = 10−8s. For LC in 100 Å random pores the second term describing the slow process dominates, whereas for 200 Å and 2000 Å cylindrical pores as well as 1000 Å random pores the contribution from the first term (fast process) is more visible. Since the slow relaxational process which does not exist in the bulk LC and broad spectrum of relaxation times (10−6 - 10)s appear not only for LC in random pores but in cylindrical as well, we conclude that differences in dynamical behavior of confined LC from that in the bulk are mainly due to the existence of the interface.

Heterogeneous Nanocomposite Materials Based on Liquid Crystals and Porous Media

1996 ◽  
Vol 457 ◽  
Author(s):  
G. P. Sinha ◽  
F. M. Aliev
Keyword(s):  
Porous Media ◽  
Liquid Crystals ◽  
Relaxation Times ◽  
Low Frequency ◽  
Porous Matrix ◽  
Nanocomposite Materials ◽  
Smectic Liquid Crystals ◽  
Porous Matrices ◽  
Frequency Relaxation ◽  
Quantitative Changes

ABSTRACTAn effective way of preparing a variety of liquid crystal based nanocomposite materials is to disperse LC in porous media with different porous matrix structure, pore size and shape. We present the results of investigations of quasiequilibrium and dynamical properties of nematic and smectic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores (porous glasses) and parallel cylindrical pores (Anopore membranes) by light scattering, photon correlation and dielectric spectroscopies. Confining LC to nanoscale level leads to quantitative changes in physical properties and appearance of new behavior which does not exist in either of the components. Relaxation of director fluctuations which is characterized by single relaxation time in the bulk LC are transformed to a process with a spectrum of relaxation times in pores, which includes extremely slow dynamics typical for glass formers. Existence of developed interface in these materials leads to new dielectric properties such as an appearance of a low frequency relaxation of the polarization and modification of dipole rotation.

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.

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.

scholarly journals Stress breaks universal aging behavior in a metallic glass

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Amlan Das ◽  
Peter M. Derlet ◽  
Chaoyang Liu ◽  
Eric M. Dufresne ◽  
Robert Maaß
Keyword(s):  
Structural Dynamics ◽  
Superposition Principle ◽  
Relaxation Times ◽  
Correlation Spectroscopy ◽  
Disordered Materials ◽  
Photon Correlation ◽  
Slowing Down ◽  
Lennard Jones ◽  
Different Temperatures

Abstract Numerous disordered materials display a monotonous slowing down in their internal dynamics with age. In the case of metallic glasses, this general behavior across different temperatures and alloys has been used to establish an empirical universal superposition principle of time, waiting time, and temperature. Here we demonstrate that the application of a mechanical stress within the elastic regime breaks this universality. Using in-situ x-ray photon correlation spectroscopy (XPCS) experiments, we show that strong fluctuations between slow and fast structural dynamics exist, and that these generally exhibit larger relaxation times than in the unstressed case. On average, relaxation times increase with stress magnitude, and even preloading times of several days do not exhaust the structural dynamics under load. A model Lennard-Jones glass under shear deformation replicates many of the features revealed with XPCS, indicating that local and heterogeneous microplastic events can cause the strongly non-monotonous spectrum of relaxation times.

scholarly journals Deciphering the intrinsic dynamics from the beam-induced atomic motions in oxide glasses

2020 ◽  
Vol 27 (5) ◽  
pp. 1247-1252
Author(s):  
Yuriy Chushkin
Keyword(s):  
Relaxation Time ◽  
Structural Relaxation ◽  
Photon Correlation Spectroscopy ◽  
Relaxation Times ◽  
Correlation Spectroscopy ◽  
Oxide Glasses ◽  
Photon Correlation ◽  
X Ray ◽  
Different Temperatures ◽  
Measured Relaxation

Probing the microscopic slow structural relaxation in oxide glasses by X-ray photon correlation spectroscopy (XPCS) revealed faster than expected dynamics induced by the X-ray illumination. The fast beam-induced dynamics mask true slow structural relaxation in glasses and challenges application of XPCS to probe the atomic dynamics in oxide glasses. Here an approach that allows estimation of the true relaxation time of the sample in the presence of beam-induced dynamics is presented. The method requires two measurements either with different X-ray beam intensities or at different temperatures. Using numerical simulations it is shown that the slowest estimated true relaxation time is limited by the accuracy of the measured relaxation times of the sample. By analyzing the reported microscopic dynamics in SiO2, GeO2 and B2O3 glasses, it is concluded that the beam-induced dynamics show rich behavior depending on the sample.

scholarly journals The Influence of Single-Walled Carbon Nanotubes on the Dynamic Properties of Nematic Liquid Crystals in Magnetic Field

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4031 ◽  
Author(s):  
Cirtoaje ◽  
Petrescu
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Continuum Theory ◽  
Elastic Continuum ◽  
Walled Carbon Nanotubes ◽  
The Impact ◽  
The Magnetic Field ◽  
Good Agreement

This article aims to study the impact of carbon nanotube dispersions in liquid crystals. A theoretical model for the system’s dynamics is presented, considering the elastic continuum theory and a planar alignment of liquid crystal molecules on the nanotube’s surface. Experimental calculation of the relaxation times in the magnetic field was made for two cases: when the field was switched on (τon), and when it was switched off (τoff). The results indicate an increase of the relaxation time by about 25% when the magnetic field was switched off, and a smaller increase (about 10%) when the field was switched on, where both were in good agreement with the theoretical values.

Sign in / Sign up

Export Citation Format

Share Document