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.

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.

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 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.

Dielectric and Optical Properties of Polymer Confined in Random Porous Matrices

2005 ◽  
Vol 899 ◽  
Author(s):  
Fouad Aliev
Keyword(s):  
Glass Transition ◽  
Light Scattering ◽  
Average Pore Size ◽  
Orientational Order ◽  
Pore Wall ◽  
Molecular Structures ◽  
Relaxation Processes ◽  
Average Pore ◽  
Porous Matrices ◽  
Dielectric And Optical Properties

AbstractWe report the results of the investigations of the influence of confinement on the glass transition and dynamics of the a-relaxation processes in poly(octylmethacrylate) (POMA) by dielectric spectroscopy. The polymer was synthesized directly in pores of the porous glass matrix with interconnected and randomly oriented pores with an average pore size of 100 nm by free radical polymerization of the monomer. We found that confinement is resulted in the reduction of the glass transition temperature Tg of the polymer. This change in Tg was mainly due to the existence of a developed pore wall-polymer interface and difference in the dynamic behavior of polymer in the surface layers compared to that in the bulk. Complementary light scattering experiments show that in 100 nm matrices containing the polymer an anomalous change in light scattering, which switches the composite from the opaque state to the transparent, in a narrow temperature range around T = 60 °C. These changes could be explained by assuming that at low temperatures (opaque state) the orientational order of the relatively long linear aliphatic side groups is induced by the inner pore surface. The assumption of the formation of the orientationally ordered regions at the pore wall in confined POMA is in agreement with the molecular structures of the polymer and the surface of silica.

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