Dielectric Relaxation in a Deeply Supercooled Liquid Crystals Confined in Random Porous Media

1998 ◽  
Vol 543 ◽  
Author(s):  
G. P. Sinha ◽  
F. M. Aliev
Keyword(s):  
Porous Media ◽  
Relaxation Time ◽  
Liquid Crystals ◽  
Dynamical Behavior ◽  
Broad Band ◽  
Pore Wall ◽  
Relaxation Processes ◽  
Main Mode ◽  
Supercooled State ◽  
Random Porous Media

AbstractLiquid crystals (LCs)—pentylcyanobiphenyl (5CB) and octylcyanobiphenyl (8CB)—were confined in random porous media with narrow pores of mean size equal to 100 Å and investigated by means of broad band dielectric spectroscopy in deeply supercooled state. In liquid crystalline phases, bulk 5CB and 8CB have two dielectrically active modes. The main mode with the relaxation time τ ∼ 10”8s is due to the rotation of molecules about their short axis, and the secondary mode is due to the tumbling motion of molecules with the relaxation time ツ ∼ 10”10s. Bulk 5CB and 8CB are nonglass formers and they crystallize at cooling. The confinement strongly influences the dynamical behavior of LCs and is resulted in qualitative changes in their properties. Deep supercooling of LCs in pores up to ∼ 150 degrees below the bulk crystallization temperature was observed. The relaxation rate of the process due to the molecular rotation in deeply supercooled state is slower than at the temperatures corresponding to nematic phase by many orders of magnitude. This slowing down is accompanied by anomalous broadening of the dielectric spectra.Other new properties observed in confined LCs are two low frequency relaxation processes absent in bulk LCs. One of these processes is due to the molecular relaxation in the surface layers at liquid crystal-solid pore wall interface. The second process is probably a collective mode due to the relaxation of the surface induced polarization. The collective process due to surface polarization and the surface molecular mode show features typical for glass formers.

scholarly journals FT-Raman study of the (sub)picosecond dynamics in genomic DNA from plant tissues

2009 ◽  
Vol 23 (5-6) ◽  
pp. 281-289 ◽  
Author(s):  
Cristina M. Muntean ◽  
Ioan Bratu
Keyword(s):  
Relaxation Time ◽  
Genomic Dna ◽  
Vibrational Energy ◽  
Raman Band ◽  
Dynamical Behavior ◽  
Relaxation Processes ◽  
Molecular Subgroups ◽  
Molecular Relaxation ◽  
Leaf Tissues ◽  
Genomic Dnas

In this paper the Raman total half bandwidths of eight genomic DNAs from leaf tissues [potato (Solanum tuberosumL.), sword fern (Nephrolepis exaltataL.), scopolia (Scopolia carniolicaJacq.), redwood (Sequoia sempervirensD. Don. Endl.), orchids (Cymbidium × hybrida), chrysanthemum (Dendranthema grandifloraRamat.) and common sundew (Drosera rotundifoliaL.)] have been measured. The dependencies of the total half bandwidths and of the global relaxation times, on DNA molecular subgroup structure and on the type of genomic plant DNA, are reported. It is shown that changes in the (sub)picosecond dynamics of molecular subgroups in genomic DNAs from leaf tissues can be monitored with Raman spectroscopy.Particularly, the Raman band parameters for the vibrations at 879 cm−1(deoxyribose, dA), 1047 cm−1(CO stretching C‒O‒P‒O‒C, dG), 1089 cm−1(P—O symmetric stretching of PO2‒), 1124 cm−1(dA), 1272 cm−1(dC, dG, dT), 1276 cm−1(dC), 1455 cm−1(deoxyribose, dA, dC, dT) and 1482 cm−1(dG, dA) of genomic leaf tissues DNAs are presented. In our study, the full widths at half-maximum (FWHM) of the bands in genomic DNAs from leaf tissues are typically in the wavenumber range from 7.8 to 23.1 cm−1. It can be observed that the molecular relaxation processes studied in this work, have a global relaxation time smaller than 1.36 ps and larger than 0.46 ps.The fastest and the slowest relaxation processes of different DNA structural subgroups, for several types of genomic DNA extracted from leaf tissue, have been analyzed. Particularly, the slowest dynamics corresponding to the vibration near 1272 cm−1takes place in the case of DNA extracted from common sundew (global relaxation time 1.36 ps).A comparison between different time scales of the vibrational energy transfer processes, characterizing several DNA complexes, has been given.We have found that the bands at 879 cm−1(deoxyribose, phosphodiester, dA) and 1455 cm−1(deoxyribose, dA, dC, dT) are suitable for the study of dynamical behavior of molecular subgroups in genomic DNA extracted from leaf tissues.Specific molecular relaxation processes, depending on the type of genomic DNA extracted from leaf tissues has been observed.

Dynamics of Director Fluctuations in Confined Liquid Crystals

2005 ◽  
Vol 899 ◽  
Author(s):  
Sarmistha Basu ◽  
Edwin Arroyo ◽  
Fouad Aliev
Keyword(s):  
Relaxation Time ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Phase ◽  
Relaxation Processes ◽  
Wall Surface ◽  
Slow Process ◽  
Nematic Director ◽  
Cylindrical Pores ◽  
Director Orientation

AbstractDynamic light scattering was applied to study the influence of randomness, boundary conditions (planar-axial and homeotropic-radial) and layer thickness (at nanoscale) of 5CB and 8CB confined to cylindrical pores and filled with Aerosil particles on relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first process is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation process (with slower relaxation time than the first one) is most likely due to the fluctuations in layers nearest the wall surface. The separation between the first and the second (slow) processes is clearer for thinner layers and the amplitude of the slow process is greater for thinner layers. This suggests that the slow process is surface related relaxation. The mode due to relaxation of fluctuations of director orientation in the vicinity of the surface of Aerosil particles was observed in filled liquid crystals as well.

HIGH RESOLUTION CALORIMETRIC STUDIES AT PHASE TRANSITIONS OF ALKYLCYANOBIPHENYL LIQUID CRYSTALS CONFINED TO SUBMICRON SIZE CYLINDRICAL CAVITIES

1995 ◽  
Vol 09 (18n19) ◽  
pp. 2247-2283 ◽  
Author(s):  
DANIELE FINOTELLO ◽  
GERMANO S. IANNACCHIONE
Keyword(s):  
Phase Transitions ◽  
Liquid Crystals ◽  
High Resolution ◽  
Specific Heat ◽  
Pore Wall ◽  
Isotropic Phase ◽  
First Order ◽  
Smectic A ◽  
Nematic Director ◽  
Scalar Order Parameter

We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphenyl liquid crystals confined to the 0.2µm diameter cylindrical pores Anopore membranes. The nematic director alignment at the pore wall is varied from homeotropic to tangential by pore surface treatment. Several phenomena are uncovered by these studies which probed the weakly first order nematic to isotropic, the continuous smectic-A to nematic and the first order smectic-A to isotropic phase transitions. The specific heat is strongly dependent on the nematic director configuration, and confinement effects are remarkably distinct according to the order of the phase transition. The influence of elastic distortions and surface ordering and disordering effects are evident. Despite considerable departures from bulk behavior with regards to specific heat peaks size, rounding and width, and transition temperature shifts, a bulk-like critical behavior appears to be retained. The formation of smectic translational order within the pores is hindered for those liquid crystals that also possess a nematic phase. The average scalar order parameter temperature dependence is extracted from the specific heat results using a simplified Landau-de Gennes type of model, and is shown to be consistent with nuclear magnetic resonance results.

scholarly journals Evaluation of the path integral for flow through random porous media

2018 ◽  
Vol 97 (4) ◽  
Author(s):  
Marise J. E. Westbroek ◽  
Gil-Arnaud Coche ◽  
Peter R. King ◽  
Dimitri D. Vvedensky
Keyword(s):  
Porous Media ◽  
Path Integral ◽  
Flow Through ◽  
Random Porous Media

Flows in random porous media: effective models

2003 ◽  
Vol 30 (4) ◽  
pp. 271-288 ◽  
Author(s):  
J.J. Telega ◽  
W.R. Bielski
Keyword(s):  
Porous Media ◽  
Random Porous Media ◽  
Effective Models

scholarly journals Statistics of highly heterogeneous flow fields confined to three-dimensional random porous media

2016 ◽  
Vol 93 (1) ◽  
Author(s):  
C. Jin ◽  
P. A. Langston ◽  
G. E. Pavlovskaya ◽  
M. R. Hall ◽  
S. P. Rigby
Keyword(s):  
Porous Media ◽  
Three Dimensional ◽  
Flow Fields ◽  
Heterogeneous Flow ◽  
Random Porous Media
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