Dynamic Light Scattering in 5CB Confined in Disordered Porous Media

1995 ◽  
Vol 407 ◽  
Author(s):  
Fouad M. Aliev ◽  
Vladimir V. Nadtotchi
Keyword(s):  
Phase Transition ◽  
Light Scattering ◽  
Volume Fraction ◽  
Wide Spectrum ◽  
Standard Form ◽  
Relaxation Times ◽  
Slow Relaxation ◽  
Isotropic Phase ◽  
Average Pore ◽  
Dynamical Scaling

ABSTRACTWe performed dynamic and static light scattering measurements in nematic LC (5CB) confined in silica porous glasses with average pore sizes of 1000 A˚ (volume fraction of pores 40%) and 100 A˚ (27%). The experiments show significant changes in physical properties of confined LC. Nematic-isotropic phase transition temperature TNI is depressed by 0.6°C in 1000 A˚ pores compared to that bulk value and this phase transition was not detected at all in 100 A˚ pores. We found that even about 20°C below bulk melting temperature the relaxational processes in confined LC were not frozen. Slow relaxation process which does not exist in the bulk LC and wide spectrum of relaxation times (10−8 –)s appear in both 100 A˚ and 1000 A˚. In 100 A˚ pores slow relaxation exists even at T corresponding to the bulk isotropic phase. Our data can not be described using the standard form of dynamical scaling variable (t/r) but they obey activated dynamical scaling with the scaling variable x = lnt/lnr.

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.

Nonlinear Optical Absorption and Related Phenomena in Liquid Crystals

2001 ◽  
Vol 709 ◽  
Author(s):  
N.V. Tabiryan ◽  
U.A. Hrozhyk ◽  
H.L. Margaryan ◽  
M.J. Mora ◽  
S.R. Nersisyan ◽  
...  
Keyword(s):  
Phase Transition ◽  
Light Scattering ◽  
Optical Absorption ◽  
Nonlinear Absorption ◽  
Nonlinear Optical ◽  
Isotropic Phase ◽  
Nonlinear Optical Absorption ◽  
Critical Opalescence ◽  
Application Potential ◽  
Large Application

SUMMARYThus, in the present paper, we reported about several processes of nonlinear absorption and transmission in dye-doped NLC: nonlinear absorption due to light induced reorientation of NLC doped by highly dichroic dyes; nonlinear transmission due to nonlinear birefringence, and self-extinguishing of the beam due to”critical opalescence,” critically enhanced light scattering at the pre-transition region of nematic-isotropic phase transition. All these processes have large application potential for laser beam control and characterization techniques.

Dielectric Spectroscopy of Nematic Liquid Crystal Confined in Random Porous Matrices

1995 ◽  
Vol 411 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Relaxation Time ◽  
Liquid Crystal ◽  
Melting Point ◽  
Dielectric Spectroscopy ◽  
Volume Fraction ◽  
Dielectric Behavior ◽  
Isotropic Phase ◽  
Polar Molecules ◽  
Average Pore ◽  
Porous Matrices

ABSTRACTWe performed dielectric spectroscopy measurements to study dynamics of dielectrically active modes of nematic liquid crystals (LC) 5CB with polar molecules confined in silica porous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%). In the nematic phase of bulk 5CB there is only one mechanism of dielectric relaxation: rotation of polar molecules around short molecular axis with relaxation time τ ∼10−8s. The spatial confinement and the existence of a highly developed interphase have a strong influence on dielectric properties of LC. We found that at temperatures about 30°C below the bulk melting point in both porous matrices the dielectric behavior of confined liquid crystal is very different from the behavior expected for solid state. The dielectric modes were not frozen in both porous matrices and we observed four well defined relaxational processes with relaxation times τ1 ∼ 10−1s, τ2 ∼10−5s, τ3 ∼10−8s (bulk like) and τ3 ∼10−9s. These four processes do not vanish even at temperatures corresponding to deep bulk isotropic phase. The relaxation time of the first process (slow) shows glass-like behavior in a wide temperature range below bulk melting point.

scholarly journals Temperature Behavior of Aqueous Solutions of Poly(2-Oxazoline) Homopolymer and Block Copolymers Investigated by NMR Spectroscopy and Dynamic Light Scattering

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1879
Author(s):  
Rafał Konefał ◽  
Peter Černoch ◽  
Magdalena Konefał ◽  
Jiří Spěváček
Keyword(s):  
Phase Transition ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Aqueous Solutions ◽  
1H Nmr ◽  
Conformational Changes ◽  
Diblock Copolymers ◽  
Relaxation Times ◽  
Temperature Behavior ◽  
Copolymer Composition

1H NMR methods in combination with dynamic light scattering were applied to study temperature behavior of poly(2-isopropyl-2-oxazoline) (PIPOx) homopolymer as well as PIPOx-b-poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2-oxazoline) (PEtOx)-b-PMeOx diblock copolymers in aqueous solutions. 1H NMR spectra showed a different way of phase transition for the main and side chains in PIPOx-based solutions. Additionally, the phase transition is irreversible for PIPOx homopolymer and partially reversible for PIPOx-b-PMeOx copolymer. As revealed by NMR, the phase transition in PEtOx-based copolymers solutions exists despite the absence of solution turbidity. It is very broad, virtually independent of the copolymer composition and reversible with some hysteresis. Two types of water molecules were detected in solutions of the diblock copolymers above the phase transition—“free” with long and “bound” with short spin–spin relaxation times T2. NOESY spectra revealed information about conformational changes observed already in the pre-transition region of PIPOx-b-PMeOx copolymer solution.

Kinetics of flowing dispersions. X. Oscillations in optical properties of streaming suspensions of spheroids

1977 ◽  
Vol 55 (24) ◽  
pp. 4243-4256 ◽  
Author(s):  
A. Okagawa ◽  
S. G. Mason
Keyword(s):  
Light Scattering ◽  
Shear Flow ◽  
General Pattern ◽  
Relaxation Times ◽  
Simple Shear Flow ◽  
Scattering Coefficients ◽  
Human Red Blood Cells ◽  
Dielectric Particles ◽  
Dilute Suspensions ◽  
Orientation Distributions

Transients in angular light scattering and turbidity of dilute suspensions of nearly monodisperse spheroidal particles undergoing simple shear flow have been investigated by combining Rayleigh–Debye light scattering theory for single dielectric particles with fluid mechanical theory for the orientation distributions of particle assemblies in shear flow. Applying shear to an initially isotropic suspension causes the orientation distributions and thus the angular scattering coefficients to oscillate. Various geometrical arrangements are considered with a view to selecting those that will maximize such rheo-optical effects.By calculating the optical scattering cross section of a single particle, the turbidity of a suspension is obtained; like the scattering coefficient, it undergoes oscillations that are damped by (1) the inevitable spread in particle shape and volume in real systems, (2) shear-induced particle interactions, and (3) rotary Brownian motion. The rates of damping, expressed as relaxation times, are considered for the three mechanisms acting alone or in concert.Preliminary measurements of the turbidity of dilute suspensions of hardened human red blood cells confirm this general pattern of behavior. Apart from their intrinsic interest, such rheo-optical effects can be used to determine a number of useful properties of dispersions.

Thermal phase transition behaviours of the blue phase of bent-core nematogen and chiral dopant mixtures under different boundary conditions

Soft Matter ◽  
2014 ◽  
Vol 10 (41) ◽  
pp. 8224-8228 ◽  
Author(s):  
Min-Jun Gim ◽  
Gohyun Han ◽  
Suk-Won Choi ◽  
Dong Ki Yoon
Keyword(s):  
Phase Transition ◽  
Boundary Conditions ◽  
Liquid Crystalline ◽  
Isotropic Phase ◽  
Different Boundary Conditions ◽  
Various Boundary Conditions ◽  
Thermal Phase Transition ◽  
Thermal Phase ◽  
Blue Phase ◽  
Chiral Dopants

We have investigated dramatic changes in the thermal phase transition of a liquid-crystalline (LC) blue phase (BP) consisting of bent-core nematogen and chiral dopants under various boundary conditions during cooling from the isotropic phase.

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