Center for Liquid Crystal Research

Bangalore, India

Center for Liquid Crystal Research

Bangalore, India
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Park M.S.,Georgia Institute of Technology | Yoon B.-J.,Georgia Institute of Technology | Park J.O.,Georgia Institute of Technology | Prasad V.,Center for Liquid Crystal Research | And 2 more authors.
Physical Review Letters | Year: 2010

Polarized Raman spectroscopy was used to investigate the development of orientational order and the degree of phase biaxiality in a bent-core mesogenic system. The values of the uniaxial order parameters P200 and P400, and biaxial order parameters P220, P420, and P440, and their evolution with temperature were determined. The temperature dependence of almost all order parameters reveals a second order transition from the uniaxial to biaxial nematic phase with P220 increasing to 0.22 before a first order transition to the smectic-C phase, upon cooling. © 2010 The American Physical Society.


Vijayaraghavan R.K.,Indian National Institute for Interdisciplinary Science and Technology | Abraham S.,Indian National Institute for Interdisciplinary Science and Technology | Rao D.S.S.,Center for Liquid Crystal Research | Prasad S.K.,Center for Liquid Crystal Research | Das S.,Indian National Institute for Interdisciplinary Science and Technology
Chemical Communications | Year: 2010

Light induced isothermal phase transition leading from smectic A* phase to a stable blue phase was achieved via photoisomerization of a chiral diphenylbutadiene based mesogen. © 2010 The Royal Society of Chemistry.


Majumdar K.C.,Kalyani University | Shyam P.K.,Kalyani University | Rao D.S.S.,Center for Liquid Crystal Research | Prasad S.K.,Center for Liquid Crystal Research
Journal of Materials Chemistry | Year: 2011

We report the occurrence of the liquid crystalline twist grain boundary phase with smectic C* blocks (TGBC*) over a very wide thermal range (∼100 °C) in cholesterol based liquid crystalline dimers comprised of an oxadiazole unit. These novel materials have been synthesized by connecting the 5-phenyl substituted oxadiazole unit to a cholesterol unit through a thio-alkyl spacer at one end and the terminal O-alkyl substituted phenyl benzoate unit through an imine linkage, at the other. The range of the TGBC* phase is found to be dramatically dependent on the length of the terminal O-alkyl chain. Interestingly, these homologues, having either TGBC*-N*-BP or TGBC*-N* phase sequence, exhibit the TGBC* phase enantiotropically. We also suggest that the specific form of oxadiazole is perhaps responsible for the phenomenon observed. © 2011 The Royal Society of Chemistry.


Sridevi S.,Center for Liquid Crystal Research | Prasad S.K.,Center for Liquid Crystal Research | Nair G.G.,Center for Liquid Crystal Research | D'Britto V.,CSIR - National Chemical Laboratory | Prasad B.L.V.,CSIR - National Chemical Laboratory
Applied Physics Letters | Year: 2010

We report electrical conductivity (σ), dielectric constant (ε) and the elastic constant measurements in a nematic liquid crystal (LC) doped with small concentrations of gold nanorods. This LC-nanoparticle complex, shows not only orders of magnitude higher σ, but also stabilizes its anisotropy. The ε data suggests an increased ordering in the nematic phase, and an improved antiparallel correlation of the molecules in the isotropic phase. Surprisingly, an anisotropic enhancement of the Frank elasticity is also seen. We suggest a possible electro/magnetomechanical conductivity switch and also provide explanations based on the aspect ratio of the nanoparticles vis-̀-vis the LC molecules. © 2010 American Institute of Physics.


Nagayama H.,Tokyo Institute of Technology | Varshney S.K.,Center for Liquid Crystal Research | Goto M.,Tokyo Institute of Technology | Araoka F.,Tokyo Institute of Technology | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2010

"Chemical Equation Presented" Chiral discs: Seemingly flat disc-like molecules form a columnar phase and spontaneously segregate into macroscopic chiral domains (deracemization). Quantum chemical calculations suggest that these molecules have a twisted axially chiral core (see picture). Their aggregation into chiral superstructures is evidenced by electronic and vibrational circular dichroism spectra.© 2010 Wiley-VCH Verlag GmbH &. Co. KGaA.


Yelamaggad C.V.,Center for Liquid Crystal Research | Prabhu R.,Center for Liquid Crystal Research | Rao D.S.S.,Center for Liquid Crystal Research | Prasad S.K.,Center for Liquid Crystal Research
Tetrahedron Letters | Year: 2010

Supramolecular liquid crystalline tris(N-salicylideneamine)s (TSANs) featuring both inter- and intra-molecular hydrogen bonding have been synthesized and characterized for the first time. These TSANs formed by condensing 3 equiv of 3,4,5-trialkoxybenzoylhydrazine with 1,3,5-triformylphloroglucinol exist as the single C3h-symmetric keto-enamine product solely, unlike the previously reported TSANs. Their self-assembly into supramolecular fluid hexagonal columnar phase over a wide thermal range is evidenced with the aid of optical microscopic, calorimetric, and powder X-ray diffraction techniques. © 2010 Elsevier Ltd. All rights reserved.


Prasada S.K.,Center for Liquid Crystal Research
Key Engineering Materials | Year: 2010

Employing actinic light to alter/stabilize a particular thermodynamic phase via the photo-isomerization of the constituent molecules is an interesting tool to investigate soft matter from a new dimension. This article focuses on the influence of different parameters, such as pressure, confinement, applied electric field, etc., on the dynamics associated with both the photochemical transition driving the equilibrium nematic to the non-equilibrium isotropic phase and the thermal back relaxation recovering the nematic phase. © (2010) Trans Tech Publications.


Tadapatri P.,Center for Liquid Crystal Research | Hiremath U.S.,Center for Liquid Crystal Research | Yelamaggad C.V.,Center for Liquid Crystal Research | Krishnamurthy K.S.,Center for Liquid Crystal Research
Journal of Physical Chemistry B | Year: 2010

We report on measurements of dielectric permittivity ε, electrical conductivity σ, elastic moduli kii, and rotational viscosity γ for a bent-core nematic liquid crystal. The static permittivity anisotropy εa ) ε∥ - ε⊥ is negative; at a given temperature in the interval 107-123 °C, ε∥ shows two relaxations falling in the frequency bands 20-200 kHz and 0.9-2 MHz; ε⊥ also shows a relaxation between 0.9 and 5 MHz. The conductivity anisotropy σa ) σ∥ - σ⊥ is negative at low frequencies; it changes sign twice at frequencies f1 and f 2 that increase with temperature, in the ranges 6.5-10 and 95-600 kHz, respectively. Surprisingly, the splay modulus k11 is considerably greater than the bend modulus k33 in the entire nematic range. Viscous relaxation is more complex than in calamitic systems involving at least a two-step process. The γ values are an order of magnitude greater compared to calamitics. © 2010 American Chemical Society.


Prasad S.K.,Center for Liquid Crystal Research | Sridevi S.,Center for Liquid Crystal Research | Rao D.S.S.,Center for Liquid Crystal Research
Journal of Physical Chemistry B | Year: 2010

In a compound exhibiting plastic (crystal B) and liquid crystalline (smectic A) phases, we report calorimetric and X-ray features that are drastically affected by confinement and orientation in Anopore membranes. Data on the untreated membranes in which the molecules aligned parallel to the pore axes, show a significant diminution in the correlation length corresponding to the positional order of the plastic phase suggesting that finite size effects can perhaps transform the plastic phase to a hexatic one. In the orthogonal case, having the molecules in the plane of the membrane, a new phase is induced, whose structural possibilities are discussed. Calorimetric measurements corroborate these results and also bring out the different thermal behaviors, not only between the bulk and the confined cases, but also between the situations wherein the orientations of the molecules are different. These findings are expected to open up a new path to understand the melting phenomenon, especially that which occurs in lower dimensions. © 2010 American Chemical Society.


Tadapatri P.,Center for Liquid Crystal Research | Hiremath U.S.,Center for Liquid Crystal Research | Yelamaggad C.V.,Center for Liquid Crystal Research | Krishnamurthy K.S.,Center for Liquid Crystal Research
Journal of Physical Chemistry B | Year: 2010

We report the results of investigations on the anisotropic electrohydrodynamic states arising in a highly conducting, planarly aligned, bent-core nematic liquid crystal driven by ac fields of frequency f in the range from 10 Hz to 1 MHz. Pattern morphologywise, two f regimes are distinguished. The low-f regime, wherein the primary bifurcation is to a state of periodic longitudinal stripes (LS), extends to an unprecedentedly large f, in the range 150-550 kHz, depending on the temperature T. This is followed by the high-f regime wherein periodic normal stripes (NS) constitute the primary instability. Both instabilities involve predominant director modulations and streamlines in the layer plane. The transitional frequency between the two regimes is linear in temperature. The curve Vc(f) shows a nonlinear increase for the LS state and decrease for the NS state. Vc(T) is an ever increasing curve close to the nematic-isotropic point for both states. The wavenumber of LS varies directly as V, and that of NS shows nearly the same behavior. The pattern period versus fis increasing for LS but decreasing for NS. Both instability states exhibit complex, light-polarization-dependent lens action. Well above the threshold, disclination loops of regular geometry appear along the stripes. They drift in a coordinated manner along the flow lines. At very high voltages, the instability turns strongly time dependent. The current models of anisotropic convection based on static electrical parameters fail to account for the observed instabilities. © 2010 American Chemical Society.

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