Model Systems for Liquid Crystal Based Dispersed Heterogeneous Materials

1996 ◽  
Vol 425 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Liquid Crystal ◽  
Physical Properties ◽  
Volume Fraction ◽  
Dynamic Properties ◽  
Structural Characteristics ◽  
Correlation Spectroscopy ◽  
Model Systems ◽  
Average Pore ◽  
Photon Correlation ◽  
Porous Matrices

AbstractPorous matrices with determined pore size, volume fraction and structure can be used as model systems to understand physical properties of dispersed liquid crystals (LC) - material important for different applications. Using photon correlation spectroscopy and dielectric spectroscopy we investigated dynamic properties of nematic liquid crystal dispersed in 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). Since the structural characteristics of these matrices are nearly independent of the temperature, all observable effects due to temperature changes can be attributed to the change in the physical properties of the second component (bC). The spatial confinement and a highly developed interface in porous matrices have a strong influence on the optical and dielectric properties of confined LC which is resulted in: appearance of at least two new dielectrically active modes, absent in the bulk and existence of slow glass-like relaxational process detected in both dielectric and photon correlation experiments.

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 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.

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.

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.

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.

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