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1.
We investigate the lasing frequency phototuning in a distributed feedback (DFB) laser based on cholesteric liquid crystals (CLC). To improve the CLC planar texture quality, we use new materials such as nematic ZhK-654 and an analog of cholesteryl oleate as a twisting additive. The selective excitation of the cis-form molecules of the azoxy-nematic is carried out with the use of a combination of an interference filter with maximum transmission at 436 nm and a cut-off filter. Using the orienting substrates with SnO2 allows us to reduce the threshold pump power by more than an order of magnitude. The proposed combination of filters for the selective excitation enables us to align the ranges of lasing wavelengths in both directions. 相似文献
2.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):151-159
In the present work, our investigation is to study the optical anisotropic properties of the binary mixture of cyano-benzilidene-p-n-octyl-oxy-aniline (CBOOA), cholesteryl nonanoate (CN), which exhibits a very interesting liquid crystalline Cho-TGB-SmC-SmA-SmB phases sequentially when the specimen cooled from its isotropic phase. These phases have been characterized by using microscopic and optical anisotropic technique. The temperature variations of optical anisotropy and electrical conductivity have been discussed. X-ray studies are supported to calculate the nano-aggregated grain size of the molecules. 相似文献
3.
Ultrasonic velocities (V) have been determined, employing a fixed path double crystal interferometer, in three cholesteric liquid crystals, namely cholesteryl propionate, cholesteryl laurate and cholesteryl myristate in their isotropic and anisotropic phases including the region of the phase transition. The variation of specific volume (v) is also studied in the same temperature range by a special dilatometer constructed for this purpose. Anomalous behaviour of ultrasonic velocity is observed near the isotropic-cholesteric phase transition in all three compounds. In the two polymesomorphic liquid crystals, namely cholesteryl laurate and cholesteryl myristate, contrary to the ultrasonic behaviour of cholesteryl stearate, prominent velocity dips are observed at cholesteric-smectic transition temperatures. The parameters adiabatic compressibility (βad) and molar sound velocity (R) are estimated and they are found to exhibit sudden jumps at cholesteric-smectic and isotropic-cholesteric transitions. The thermal expansion and temperature co-efficient of compressibility are found to show abnormal increase near the phase transition indicating the existence of large-magnitude pre-transitional effects near the phase transition. A comparative study of the ultrasonic behaviour of six aliphatic esters of cholesterol has shown that the magnitude of the velocity dip observed at the isotropic-cholesteric transition increased with increase of molecular weight and only cholesteryl acetate shows deviation. 相似文献
4.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,625(1):99-105
In the present work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds namely, decyloxy benzoic acid (DBA), and cholesteryl chloride (ChCl), which exhibits different liquid crystalline phases with reentrant smectic-A phase. The reentrant smectic-A phase has been observed at different concentrations and at different temperatures. The existence of reentrant smectic-A phase has been observed by optical microscopic studies. The temperature variation of optical anisotropy, X-ray and helical pitch of the cholesteric (N*) phase has also been discussed. 相似文献
5.
Cornelia Motoc RǎZvan Mitrol Maria Honciuc Constantin Roşu 《Molecular Crystals and Liquid Crystals》2013,570(2-4):277-288
The growth kinetics of cholesteric spherulites of cholesteryl laurate-cholesteryl caprilate mixture (50: 50% by weight) is investigated. It is show that the nucleation is bidimensional and the growth is determined by the orientational relaxation of the molecules near the interface. The same growth mechanism holds when the nucleation was followed under d.c. electric fields; in this case the growth rates were lower. The electric field effects on growth kinetics can be explained by considering both changes in critical supersaturation and changes in some coefficients associated with dissipative effects during relaxation. 相似文献
6.
The axis of polarization of light propagating through a cholesteric liquid crystal rotates with the angular rotation per distance traversed termed rotatory power. The rotation is due to the helical array of the molecules rather than due to the individual molecules as is found, for instance, with light being propagated through a sugar solution. The De Vries model for rotatory power of a cholesteric liquid crystal is generalized using multiple scaling theory to include light traveling at an oblique angle to the pitch axis. The resulting expression is tested experimentally using a mixture of cholesteryl oleyl carbonate and cholesteryl chloride. 相似文献
7.
Samiul Hoque Narendra Nath Dass Krishna Gopal Bhattacharyya 《Molecular Crystals and Liquid Crystals》2014,592(1):149-162
Poly(cholesterylacrylatesulfone) (PCHAS) and poly(cholesterylacrylatesulfone-co-1-hexene)s (PCHASHs) at different ratios are synthesized from the monomer cholesteryl acrylate. The liquid crystalline phases are observed under a hot stage fitted with a polarizing optical microscope. The polysulfone and copolysulfones are characterized by FT-IR, 1H-NMR, DSC, and TGA techniques. From SEM (EDX) the qualitative amounts of elemental sulfur found in PCHAS and PCHASH11 are 2.90 weights (%) and 4.39 weights (%), respectively. The GPC data using THF as the solvent shows that the number average molecular weight of the PCHAS is 5268 g/mol and the molecular weights of the PCHASHs are higher than the PCHAS. 相似文献
8.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):115-123
We report the results of our studies on the optical and thermal properties of the mixture of terephthalidene-bis-4, n-alkylaniline and cholesteryl nonanoate, which exhibits very interesting liquid crystalline mesophases such as cholesteric, twisted grain boundary, smectic-A, smectic-C*, smectic-C, smectic-I, and smectic-G, sequentially when the specimen is cooled from its isotropic phase. These phases have been characterized by using microscopic techniques. The temperature variations of optical anisotropy, electrical conductivity, ultrasonic velocity, and molar and adiabatic compressibility have also been discussed. 相似文献
9.
V. V. Grebenev A. E. Voloshin M. S. Lyasnikova N. A. Dyatlova 《Crystallography Reports》2014,59(6):923-927
It is shown that interference can be implemented in the optical scheme of an Olimpus Lext-3000 laser scanning microscope. The occurring interference patterns are differently localized in space, depending on the experimental conditions. Interference from opposite crystal (volume) faces can be observed under certain conditions, which makes it possible to visualize (with a high sensitivity) defects that are invisible in polarized light and the surface relief. Misorientations and deformations in a crystal can be estimated. Our analysis allowed us to interpret the in situ observed interference pattern from growing lisozyme protein crystals and K2Co(SO4)2 · 6H2O crystals. 相似文献
10.
Recent theoretical work by numerous authors has indicated that pretransitional properties of the isotropic phase are highly dependent on the chirality of the nearby ordered phase. To test this aspect of the theories, we present results on the optical rotatory power in the isotropic phase for a series of four cholesteryl esters of varying chirality. The most important finding is that the separation between the first and second order transition temperatures decreases with an increase in chirality. However, the results of a recent experiment which claimed to present evidence for strong coupling between the structural modes of the ordered phase are not substantiated by the new measurements reported here. 相似文献
11.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):100-107
The multi-component system of cholesteryl chloride (ChCl), dodecyl trimethylammonium chloride (DTAC), and ethylene glycol (EG) exhibits very interesting liquid crystalline mesophases like cholesteric and SmA, SmC, and SmB phases sequentially when the specimen is cooled from its isotropic phase. These phases have been characterized by employing optical and X-ray studies. Pitch of the cholesteric phase has been calculated and discussed. Variation of pitch from the cholesteric phase to smectic phase is smooth and continuous. The temperature variation of optical anisotropy and electrical-conductivity has also been discussed. It has been found that wherever there is a phase transition, the value of electrical susceptibility changes appreciably. 相似文献
12.
The interaction with donor p-n-alkylbenzoic acid and acceptor nonyl-p-hydroxy benzoate molecules was studied. The likely association of these molecules to complexes is studied by intermolecular hydrogen bonding. The textures are observed by polarizing optical microscope with corresponding transitions confirmed by differential scanning calorimetry. The molecular complexes exhibited enantiotropic crystal G phases in both heating and cooling cycles. The relevant functional groups C═O, C-O and OH in formation of molecular complexes are attributed with spectral shifts in infrared spectra and further with absorption studies. The proton NMR studies convinced the structural aspects of hydrogen bonded structure. Crystal parameters were studied with powdered X-ray diffraction. The results show that constituent molecules self organize through intermolecular hydrogen bonding in the formation of crystal G phase. 相似文献
13.
14.
Maria Regina Alcantara José Atilio Vanin 《Molecular Crystals and Liquid Crystals》2013,570(3-4):333-340
Optical signs of type I and II micellar cholesteric lyotropic mesophases were for the first time determined. Lyomesophases were prepared from the following amphiphiles: potassium l-N-lauroyl-serinate, potassium laurate, sodium decylsulfate, cesium decylsulfate and decyl-ammonium chloride. Cholesterol was added to all mesophases in order to obtain the chevron pattern for magnetically oriented samples. The method involves the direct observation of the textures at the polarizing microscope. Using a quartz-wedge retardation plate the directions of the slow and fast light vibration components are determined. This method is simpler than the usual observation, under conoscopic illumination, of the basal interference figure which is hardly obtained in micellar lyotropic cholesteric mesophases. All type I cholesteric lyotropic mesophases here investigated exhibited a positive optical sign, whereas all type II cholesteric lyomesophases showed a negative birefringence. 相似文献
15.
Abstract A new approach to monitoring of vitamin D synthetic capacity of UV solar/artificial radiation is described. Nematic liquid crystal (LC) was converted into cholesteric phase by chiral dopant of 7-dehydrocholesterol (provitamin D3), and the effects of UV irradiation were studied using spectral and polarized observations. Significant changes in optical characteristics of the LC films depending on UV exposure were observed as a result of UV initiated photoisomerization that changed helical twisting power of dopant molecules. 相似文献
16.
M. Sisido K. Kawaguchi K. Takeuchi Y. Imanishi 《Molecular Crystals and Liquid Crystals》2013,570(2):263-275
Fluorescence from cholesteric liquid-crystalline mixture containing cholesteryl 3-(l-pyrenyl)propanoate was measured under dc and ac electric field applied parallel to the helix axis. The excimer fluorescence of the pyrenyl chromophore increased and decreased its intensity reversibly upon turning the electric field on and off. Similar electric field effects were observed for such chromophores as tetracene, perylene, and 9,10-diphenylanthracene doped in the cholesteric mixture. The electric-field effect was observed only for fluorescence transitions which show left-handed circularly polarized fluorescence, indicating that only transitions which are polarized perpendicular to the optic axis in a quasi-nematic layer exhibit the effect. The experimental results were found to be intimately connected to the onset of the Helfrich periodic distortion of a planar structure. 相似文献
17.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,625(1):93-98
The ternary system of 4’-n-octyloxy-4-cyanobiphenyl (8OCB), 4-cyano-4’-Pentyl teraphenyl (5CT), and cholesteryl nonanoate (CN) exhibits very interesting unusual liquid crystalline phase of N* (cholesteric), twisted grain boundary (TGB) phase, and re-entrant smectic-A (ReSmA) phases and it is obtained sequentially when the specimen is cooled from isotropic phase. These phases have been characterized by using X-ray and optical texture studies. The temperature variations of electrical conductivity have been discussed. 相似文献
18.
Si1-xGex mixed crystals with 5 at% Ge concentration have been grown by the pulling-down technique using a crucible with multi-capillary channels. The unique feature of the technique is that Ge solute concentration of the small molten zone is maintained constant due to the condition of no back diffusion of solute through the capillary channels, and that the diffusion-controlled solute transport causes the effective distribution coefficient to be unity. The Ge concentration was measured by the electron probe microanalysis and observed to be homogeneous along both the longitudinal and radial directions. The two-dimensional distribution on the whole cross section was also found to be uniform. 相似文献
19.
The geometrical anisotropy in the shape of swallow-tailed ST liquid crystalline molecules results in an extremely strong tendency of an antiparallel order in the short range. Dielectric measurements on a binary system of a ST and a double ST compound show that even at a mole fraction of 0.5 this effect can be observed. The strong deviations from the statistical distribution of the directions of the molecular long axis is caused by the asymmetric repulsive forces and the dipole-dipole interaction. 相似文献