| 1. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Dual Frequency Addressable Optical Device
- 2005
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Ingår i: Journal of Applied Physics. - 1089-7550. ; 97:9
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Tidskriftsartikel (refereegranskat)abstract
- We propose a photonic switch employing a liquid-crystalline material. The material exhibits a change in the sign of the dielectric anisotropy switching from a positive to a negative value at a certain crossover frequency. By application of an electric field this phenomenon can be used to alter the orientation of the sample between two orthogonal directions leading to a large change in the optical transmission characteristics of the medium. Here we demonstrate that this feature can be realized by an unpolarized ultraviolet UV beam, owing to the photoisomerization of the constituent azobenzene molecules. Possible usage of this for optically driven display devices and image-storage applications are suggested.
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| 2. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Dynamic Self-Assembly of the Liquid Crystalline Smectic-A Phase
- 2005
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Ingår i: Advanced Materials. - 1521-4095. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- A photoinduced transition in an azobenzene-containing liquid crystal leads to a phase that does not exist in the thermal cycle. The smectic A phase is induced and stabilized only in the presence of UV light, producing fan-shaped focal conic textures typical of the SmA phase, as observed by polarized-light microscopy (see Figure). This dynamic self-assembly is explained by photoinduced nanophase segregation and a frustrated spin-gas model.
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| 3. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Evidence of Worm-like micellar behavior in Chromonic liquid Crystals: Rheological, X-ray
- 2007
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Ingår i: J.Phys.Chem.B. ; 111:33
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Tidskriftsartikel (refereegranskat)abstract
- We report rheological, X-ray, and dielectric investigations on a chromonic liquid-crystalline system formed by aqueous solutions of a food coloring agent, Sunset Yellow, in the absence and upon addition of salt. The salt-concentration dependence of the steady-state viscosity at low shear rates has a non-monotonic variation and is qualitatively similar to the behavior seen in wormlike micellar systems, a surprising result since chromonic systems are expected to be non-micellar in character. More interestingly, for a particular low concentration of the salt (20 mM), the viscosity increases by 3 orders of magnitude in comparison with that of the pure chromonic material. The dynamic (oscillatory) rheological data bring out features which can be described in terms of a microstructure formation. X-ray and dielectric studies show that certain characters of the aggregates formed by the Sunset Yellow molecules are not altered by the addition of salt.
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| 4. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Nonequilibrium Liquid Crystalline Layered Phase Stabilized by Light
- 2007
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Ingår i: J.Phys.Chem.B. ; 111:2
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Tidskriftsartikel (refereegranskat)abstract
- The ability of light to alter/stabilize a particular thermodynamic phase is a power tool to investigate condensed matter from a new dimension. This field of photoinduced phase transitions is currently an important area of research. Being elastically soft and having subtle changes between its many phases a liquid crystal material is an attractive medium to investigate such light-driven phase transitions. The attraction is partly due to the large birefringence changes accompanying these transitions that are useful in developing photonic devices. In all of the cases reported to date, the photoinduced transition always leads to a phase that in any case exists in the thermal cycle. Recently we reported the first exception to such an established phenomenon (AdV. Mater. 2005, 17, 2086). The guest-host ternary mixture consisting of the photoactive azobenzene guest molecules does not exhibit smectic A phase in the absence of UV radiation. However, the smectic A phase is induced and stabilized only in the presence of UV light. In this paper, we map out hitherto unexplored temperature versus UV intensity phase diagrams for various mixtures, which illustrate that light mimics, in a limited sense, the role of a thermodynamic parameter such as, for example, pressure. The threshold UV intensity required to photodrive the appearance of the smectic A phase is seen to have a strong concentration dependence. Our studies also suggest the possibility of observing a double critical point by employing the UV intensity as a fine-tuning parameter.
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| 5. |
- Hegde, Gurumurthy, 1979, et al.
(författare)
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Photoinduced Effects in the Vicinity of the Smectic-A-Smectic-CA* Transition; Polarization
- 2006
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Ingår i: Physical Review E. - 1550-7998. ; 73:1
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Tidskriftsartikel (refereegranskat)abstract
- We report detailed measurements of the photoinduced effects on the electric polarization, tilt angle, response time, and rotational viscosity in the vicinity of the smectic-A–antiferroelectric-smectic-C Sm-CA * transition of a guest-host system consisting of photoactive azobenzene-based guest molecules and nonphotoactive host molecules. In the Sm-CA * phase all the parameters, except the tilt angle, exhibit both the primary and secondary photoferroelectric effects. The tilt angle dependence of the polarization in the absence of light and in light-on conditions have been analyzed in terms of the predictions of the generalized mean-field and microscopic models.
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| 6. |
- Krishna Prasad, M. Bala, et al.
(författare)
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Metal fractionation studies in surfacial and core sediments in the Achankovil River basin in India
- 2006
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Ingår i: Environmental Monitoring & Assessment. - : Springer Science and Business Media LLC. - 0167-6369 .- 1573-2959. ; 121:1-3, s. 77-102
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Tidskriftsartikel (refereegranskat)abstract
- The Fractionation of Fe, Zn, Cu, Pb, Mn and Cd in the sediments of the Achankovil River, Western Ghats, India using a sequential extraction method was carried out to understand the metal availability in the basin for biotic and abiotic activities. Spatial distribution of heavy metals has been studied. Sediment grain size has significant control over the heavy metal distribution. The fluctuations in their concentration partly depend upon the lithology of the river basin and partly the anthropogenic activities. The sediments are dominated by sand and are moderately to strongly positively skewed and are very leptokurtotic in nature. The quartzite and feldspars are abundant minerals along with significant amount of mica with low clay content. The core sediments show increasing trend of heavy metal concentration with depth due to the recent addition of anthropogenic sources and post-diagenic activities. Significant amount of Cd (18%) was found in carbonate fraction, which may pose environmental problems due to its toxic nature. Small concentrations of metals, except Cd and Cu, are in exchangeable fraction, which indicate low bio-availability. Enrichment Factor (EF) for individual metals shows the contribution from terrregious and in part from anthropogenic sources. Selective Sequential Extraction (SSE) study shows the variation in specific metal distribution pattern, their distribution in different phases and their bio-availability. Maximum amount of the metals were bound to the non-residual fractions (mainly Fe-oxides). Overall, bio-availability of these micronutrients from sediments seems to be very less. Non-residual phase is the most important phase for majority of heavy metals studied. Among the non-residual fraction, maximum amount of the heavy metals bound to Fe-oxides. The study high lights the need for in-depth study of heavy metals distribution and fractionation in the smaller river basins to get precise information on the behavior and transport of heavy metals in the fluvial environment and their contribution to the world ocean.
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