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Krishna S Prasad - One of the best experts on this subject based on the ideXlab platform.
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effect of zno nanoparticles on the morphology dielectric electro optic and photo luminescence properties of a confined ferroelectric liquid crystal material
2018Co-Authors: Divya Jayoti, Praveen Malik, Krishna S PrasadAbstract:Abstract The influence of spherical zinc oxide nanoparticles (ZnO-NPs) incorporated in low concentrations (0.45, 0.7, 1.0 wt/wt%) into a polymer confined ferroelectric liquid crystal (FLC) has been investigated. Varying the concentration of ZnO-NPs is found to have a profound impact on the morphology of the polymer dispersed ferroelectric liquid crystal (PDFLC) composites. With increasing ZnO-NP content, the real and imaginary parts of the permittivity and the dielectric strength of a relevant Relaxation mode depict an increase. However, the associated Relaxation Frequency shifts to lower values; a concomitant increase in spontaneous polarization is also observed. The response time of the composites slightly improved on doping with the ZnO-NPs. The changes in electro-optic and dielectric parameters are explained in terms of change in elastic energy as well as surface morphology of the composites. Interestingly, the polymer/liquid crystal environment is also seen to enhance the photoluminescence response of confined FLC.
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enhancement of electrical conductivity dielectric anisotropy and director Relaxation Frequency in composites of gold nanoparticle and a weakly polar nematic liquid crystal
2014Co-Authors: Krishna S Prasad, Vijay M Kumar, T Shilpa, C V YelamaggadAbstract:We report complex permittivity characteristics in composites of gold nanoparticles (GNP) and a weakly polar nematic liquid crystal possessing a low Frequency director Relaxation. Differential calorimetric measurements show that the inclusion of GNP has a strong influence on the isotropic–nematic (fluid–orientational fluid) transition temperature as well its first order character in terms of the transition entropy. The absolute value of conductivity increases by two to three orders of magnitude with respect to that for the host liquid crystal and its concentration dependence is demonstrated to be described by the percolation scaling law generally observed in composites of metal particles and polymers. However, the obtained exponent is much smaller, possibly owing to thermal fluctuations present in the fluid-like nematic medium. The activation energy governing the temperature dependence of conductivity is much higher in the nematic than in the isotropic phase. The Frequency dependence of the ac conductivity exhibits a critical Frequency that is concentration-dependent, but the exponents obtained defy Jonscher's Universal Response principle. A surprising feature is the observation of a substantial increase of not only the principal permittivity values, but their anisotropy as well. These studies also constitute the first report on the influence of GNP on the director Relaxation mode of nematics. In contrast to the behaviour of the static permittivity, the dynamics of the system as measured using the director Relaxation is seen to become faster with the presence of GNP. We provide an explanation for this antagonistic behaviour in terms of the alignment of the liquid crystal molecules in the vicinity of GNP, and the importance of the weak polarity of the liquid crystals used.
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experimental investigations on weakly polar liquid crystal aerosil composites
2006Co-Authors: Chethan V Lobo, Krishna S Prasad, C V YelamaggadAbstract:We have carried out differential scanning calorimetric and dielectric studies on composites of hydrophilic aerosil with a liquid crystal that does not possess a terminal polar group. While the shift in the nematic–isotropic transition temperature is in agreement with the general behaviour observed for such composites, the dielectric studies show, contrary to the commonly observed feature, that there is a systematic increase in the Relaxation Frequency associated with the rotation of the molecules around their short axis, as the aerosil concentration in the composite is increased.
A M Biradar - One of the best experts on this subject based on the ideXlab platform.
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bismuth ferrite nanoparticles for modulation of helical structure at the interface of ferroelectric liquid crystal and substrate
2020Co-Authors: Sidra Khan, Amit Choudhary, Jai Prakash, Shikha Chauhan, A M BiradarAbstract:We report the impact of dispersion of bismuth ferrite nanoparticles (BF-NPs) on the helical structure of a ferroelectric liquid crystal (FLC) in two ways: on the surface and into the bulk of FLC. The optical textural observations of the FLC sample cell with BF-NPs on the surface of the substrate show a remarkable change of three different domains having varied molecular orientation in comparison to pure and bulk dispersed FLC, where only two types of domains of different molecular orientations are observed at room temperature. These observations have confirmed distinct molecular dynamics in all the samples. The dispersion of BF-NPs in the bulk of FLC causes a slight shift in a chiral smectic C* (SmC*)–chiral smectic A* (SmA*) phase transition toward a higher temperature. The Goldstone mode (GM) Relaxation Frequency of the bulk dispersed sample is shifted toward the higher Frequency as the temperature is increased and finally is suppressed once the transition from the SmC* phase to the SmA* phase occurs. A...
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non linear behaviour of phason mode with bias field in ferroelectric liquid crystals
2010Co-Authors: Anil Kumar, Jai Prakash, A M BiradarAbstract:The decrease in Goldstone mode Relaxation Frequency with applied dc electric field in a deformed helix ferroelectric liquid crystal (DHFLC) is observed at room temperature. This decrement in Relaxation Frequency is observed at very low dc electric fields (below the threshold voltage, i.e. around 2 V). This behaviour is compared with that of conventional ferroelectric liquid crystals (FLCs) where the Relaxation Frequency increases with the applied dc electric field. It is observed that a low dc electric field is insufficient to unwind the helix completely due to the higher rotational viscosity of the DHFLC material. Moreover, the DHFLC molecules take more time in the winding (Smectic C–Smectic C∗) process, compared to the FLC molecules, which take comparatively less helix winding time because of their low viscosity. The decrease in Relaxation Frequency in DHFLCs with bias has been attributed to the critical balancing amongst the electric torque, elastic constraints and rotational viscosity in a certain reg...
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dielectric Relaxation of dye doped ferroelectric liquid crystal mixture a comparative study of smectic c and smectic a phase
2007Co-Authors: Abhishek Kumar Srivastava, Rajiv Manohar, J P Shukla, A M BiradarAbstract:Present investigation reports dielectric Relaxation behaviour of a ferroelectric liquid crystal mixture with and without doping of Anthraquinone dye. Dielectric properties of dye doped and pure ferroelectric liquid crystal mixture has been investigated as a function of temperature and Frequency. In the present investigation Goldstone mode has been observed in smectic C* (SmC*) phase, while soft mode is observed in smectic A (SmA) phase and they have been explained with the help of Cole–Cole function. It has also been observed that the addition of dye strengthens the helix in SmC* phase, which is indicated by higher Relaxation Frequency and dielectric strength of the dye doped ferroelectric liquid crystal mixture. The SmC*–SmA phase transition point become sharper with the addition of dye in ferroelectric liquid crystal material and also shifted towards lower temperature side.
Sadakatsu Nishikawa - One of the best experts on this subject based on the ideXlab platform.
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dynamic interaction between alkylammonium ions and β cyclodextrin by means of ultrasonic Relaxation
2005Co-Authors: Kyohei Yamaguchi, Takanori Fukahori, Sadakatsu NishikawaAbstract:Ultrasonic absorption measurements in the Frequency range from 0.8 to 220 MHz were carried out in aqueous solutions of pentylammonium chloride (PEACL) and hexylammonium chloride (HEACL) with beta-cyclodextrin (beta-CD) at pH approximately 7.2 and 25 degrees C. A single Relaxational absorption was attributed to a perturbation of a chemical Relaxation associated with the formation of a complex between beta-CD and the alkylammonium chlorides. The rate and equilibrium constants for the complexation reaction were determined from the concentration dependence of the Relaxation Frequency. Increasing the chain length of the alkylammonium ion led to an increase in the stability of the complex and slowed the exit rate of the ion from the beta-CD cavity. The standard volume change of the reaction was obtained from a maximum absorption per wavelength and was attributed to water molecules being expelled from the cavity with concomitant alkylammonium ion insertion.
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ultrasonic Relaxation due to complexation reaction between β cyclodextrin and alkylammonium ions
2003Co-Authors: Sadakatsu Nishikawa, And Kyohei Yamaguchi, Takanori FukahoriAbstract:Ultrasonic absorption coefficients in an aqueous solution of propylammonium chloride (PACL) and butylammonium chloride (BACL) (pH ≈ 7.2) were measured in the presence and absence of β-cyclodextrin (β-CD) at 25 °C in the Frequency range 0.8−220 MHz. There was no Relaxation in the solution of individual alkylammonium chloride or β-CD. Also, in the solution with PACL and β-CD, the Relaxation was not observed. However, a single Relaxational absorption was found in the solution of BACL when β-CD coexisted. The cause of the Relaxation was attributed to a perturbation of a chemical equilibrium associated with an interaction between β-CD and the butylammonium ion from the concentration dependence of the Relaxation Frequency and the maximum absorption per wavelength. The rate and thermodynamic constants were determined for the association and dissociation reactions of the complex in the system of BACL with β-CD. The results obtained were compared with those for other similar systems, e.g., propionate ion or propio...
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molecular recognition kinetics of leucine and glycyl leucine by β cyclodextrin in aqueous solution in terms of ultrasonic Relaxation
2002Co-Authors: Takanori Fukahori, Takaho Ugawa, Sadakatsu NishikawaAbstract:Ultrasonic absorption coefficients in the Frequency range of 0.8−95 MHz were measured in aqueous solution of leucine and glycyl-leucine in the presence and absence of β-cyclodextrin (β-CD) at 25 °C. A single Relaxational absorption was found in both solutions although it was not observed in the absence of β-CD. The cause of the Relaxation was attributed to a perturbation of a chemical equilibrium associated with an interaction between β-CD and the amino acid or the dipeptide. The rate and thermodynamic constants for the association and dissociation reaction of the complex in the system of glycyl-leucine and β-CD were determined from the concentration dependence of the Relaxation Frequency and the maximum absorption per wavelength. On the other hand, another analysis was applied for the system with leucine and β-CD to calculate the rate and thermodynamic constants due to the indistinguishable concentration dependence of the Relaxation Frequency. Therefore, first the equilibrium constant was estimated from ...
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molecular recognition kinetics of β cyclodextrin for several alcohols by ultrasonic Relaxation method
2001Co-Authors: Sadakatsu Nishikawa, And Takaho Ugawa, Takanori FukahoriAbstract:Ultrasonic absorption coefficients in aqueous solutions of 2-propanol, 2-butanol, and 2-methyl-1-propanol (guest) in concentrations less than 0.40 mol dm-3 with β-cyclodextrin (host) in the range below 0.011 mol dm-3 were measured in the Frequency range 0.8−95 MHz at 25 °C. A single Debye-type Relaxational absorption was found only when both solutes coexisted. From the concentration dependences of the Relaxation Frequency and the amplitude of the Relaxation, the cause of the observed Relaxation was attributed to a perturbation of a chemical equilibrium associated with a dynamic interaction between β-cyclodextrin and the alcohols. The rate and thermodynamic parameters for the dynamic interaction were determined, and the results were compared with those for other alcoholic systems with β-cyclodextrin, which were reported previously. The isomeric effect of the guests on the dynamic interaction with β-cyclodextrin was considered and it is deduced from the experimental results that the hydrophobicity of the gu...
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kinetic and thermodynamic study of syn anti glycosyl isomerization in aqueous solutions of amp adp and atp by ultrasonic Relaxation methods
1999Co-Authors: Sadakatsu Nishikawa, Naoki Kuramoto, Hua Huang, Frank JordanAbstract:Ultrasonic absorption coefficients in aqueous solutions of adenosine 5‘-triphosphate (ATP) were measured at 25 °C as a function of concentration and pH in the Frequency range from 0.8 to 220 MHz. An ultrasonic Relaxational absorption with two Relaxation frequencies was observed near pH 3. However, above pH 12, only a single Relaxational absorption was detected at around 100 MHz, and this Relaxation is the focus of this report. The Relaxation Frequency is independent of the concentration and pH at around pH 12, and the maximum absorption per wavelength increases linearly with concentration. From these results, the cause of the Relaxation was attributed to a syn−anti glycosyl isomerization reaction of ATP. The rate of the rotational motion in ATP was found to be smaller than that for ADP and greater than those for AMP and adenosine. These results are discussed in relation to the charge distribution and the effect of the size of the phosphate group of the nucleotides. To examine the reaction mechanism furthe...
Alexandro Castellanos - One of the best experts on this subject based on the ideXlab platform.
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fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes i experimental measurements
2000Co-Authors: Nicolas G Green, Hywel Morgan, Antonio Ramos, Antonio G Gonzalez, Alexandro CastellanosAbstract:Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the charge Relaxation Frequency of the electrolyte. The velocity of latex tracer particles was measured as a function of applied signal Frequency and potential, electrolyte conductivity, and position on the electrode surface. The data are discussed in terms of a linear model of ac electroosmosis: the interaction of the nonuniform ac field and the induced electrical double layer.
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Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. II. A linear double-layer analysis
2000Co-Authors: A. González, Alexandro Castellanos, A. Ramos-paz, Nicolas G Green, Hywel MorganAbstract:Frequency-dependent fluid flow in electrolytes on microelectrodes subjected to ac voltages has recently been reported. The fluid flow is predominant at frequencies of the order of the Relaxation Frequency of the electrode-electrolyte system. The mechanism responsible for this motion has been termed ac electro-osmosis: a continuous flow driven by the interaction of the oscillating electric field and the charge at the diffuse double layer on the electrodes. This paper develops the basis of a theoretical approach to this problem using a linear double layer analysis. The theoretical results are compared with the experiments, and a good correlation is found.
Hywel Morgan - One of the best experts on this subject based on the ideXlab platform.
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fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes i experimental measurements
2000Co-Authors: Nicolas G Green, Hywel Morgan, Antonio Ramos, Antonio G Gonzalez, Alexandro CastellanosAbstract:Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the charge Relaxation Frequency of the electrolyte. The velocity of latex tracer particles was measured as a function of applied signal Frequency and potential, electrolyte conductivity, and position on the electrode surface. The data are discussed in terms of a linear model of ac electroosmosis: the interaction of the nonuniform ac field and the induced electrical double layer.
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Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. II. A linear double-layer analysis
2000Co-Authors: A. González, Alexandro Castellanos, A. Ramos-paz, Nicolas G Green, Hywel MorganAbstract:Frequency-dependent fluid flow in electrolytes on microelectrodes subjected to ac voltages has recently been reported. The fluid flow is predominant at frequencies of the order of the Relaxation Frequency of the electrode-electrolyte system. The mechanism responsible for this motion has been termed ac electro-osmosis: a continuous flow driven by the interaction of the oscillating electric field and the charge at the diffuse double layer on the electrodes. This paper develops the basis of a theoretical approach to this problem using a linear double layer analysis. The theoretical results are compared with the experiments, and a good correlation is found.
