Estimation of entropy and enthalpy of a nematic liquid crystal using time domain reflectometry studies

Dielectric relaxation behavior of molecules in their pure form, a non-polar solvent, or mixtures of these substances at different microwave frequencies and over a range of temperatures and concentrations give an idea about inter- and intra-molecular forces. Such studies enable one to calculate thermodynamic parameters like change of activation energy for dipole orientation (??G*), enthalpy (??H*), and entropy (??S*) of activation. Such studies in liquid crystals give additional information about the molecular behavior in different phases of liquid crystal under study. An experimental investigation on verity of systems is necessary to draw quantitative conclusions regarding the system of the molecules which are not studied so as to examine if the results obtained are in favor or against, to the general conclusions already arrived at, in other systems. With this in view, the complex dielectric permittivity spectra of p-pentyl phenyl-p-propylbenzoate (PPPB) a nematic liquid crystal are obtained using Time Domain Reflectometry (TDR) method over a frequency range 10?MHz?C10?GHz at various temperatures covering both nematic and isotropic phases. The thermodynamic functions calculated using these measurements are presented and discussed in this article.     

Thermodynamic parameters of dilute solutions of a polymer in benzene at varying temperatures and concentrations

Dilatometric studies of solutions of four different mole fractions of poly(ethylene glycol) of average molecular mass 400 g mol^?1 dissolved in benzene have been performed to estimate molar volumes (V) and volume expansion coefficients (α) at different temperatures. From these, thermodynamic parameters appropriate to these solutions have been evaluated at different temperatures ranging from 299 to 328 K. These parameters have been employed to collect and discuss the information on molecular structure, molecular order, molecular packing, polymer segment extension, and molecular interactions.     

Solvent Effect on Absorption and Fluorescence Spectra of Three Biologically Active Carboxamides (C<Subscript>1</Subscript>, C<Subscript>2</Subscript> and C<Subscript>3</Subscript>). Estimation of Ground and Excited State Dipole Moment from Solvatochromic Method Using Solvent Polarity Parameters

The absorption and fluorescence spectra of three Carboxamides namely (E)-2-(4-Chlorobenzylideneamino)-N-(2-chlorophenyl)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₁), (E)-N-(3-Chlorophenyl)-2-(3, 4-dimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₂) and (E)-N-(3-Chlorophenyl)-2-(3, 4, 5-trimethoxybenzylideneamino)-4, 5, 6, 7-tetrahydrobenzo[b]thiophene-3-carboxamide (C₃) have been recorded at room temperature in solvents of different polarities using dielectric constant (ε) and refractive index (n). Experimental ground (μ_g) and excited (μ_e) state dipole moments are estimated by means of solvatochromic shift method and also the excited dipole moments are estimated in combination with ground state dipole moments. It was estimated that dipole moments of the excited state were higher than those of the ground state of all three molecules. Further, the changes in dipole moment (Dm \Delta \mu ) were calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter (E_T^N E_T^N ) and the values are compared.     

Homozygous mutation of focal adhesion kinase in embryonic stem cell derived neurons: normal electrophysiological and morphological properties in vitro

Background  

Genetically manipulated embryonic stem (ES) cell derived neurons (ESNs) provide a powerful system with which to study the consequences of gene manipulation in mature, synaptically connected neurons in vitro. Here we report a study of focal adhesion kinase (FAK), which has been implicated in synapse formation and regulation of ion channels, using the ESN system to circumvent the embryonic lethality of homozygous FAK mutant mice.     

Preparation and characterization of Eu(3+) doped powder spinel phosphors (MgAl(1.8)Y(0.2-x)O(4))

The photoluminescence (PL) studies of powder phosphors are under rigorous study in view of the applications they have in the field of technology. Different methods are available for the preparation of rare earth ions doped in different host environment of powder phosphors. In the present work, a novel route known as sol-gel technique is employed to prepare spinel phosphor MgAl(1.8)Y(0.2-x)O(4):Eu(x) (x = 2-6 mol%). Then the studies have been carried out to optimize the dopant concentration in the host lattice with the help of photoluminescence spectra. These phosphors have displayed bright red color under UV source. The emission intensities were determined and the relative fluorescence intensities have been estimated. The richness of the red color has been verified by determining their chromaticity coordinates (X, Y) from the CIE standard charts. With the help of XRD, electron spin resonance (ESR), and photo-acoustic (PA) spectra of the samples prepared are also used for the confirmity of the host and analyzing of the data.     

Optical,physical and structural studies of vanadium doped P2O5–BaO–Li2O glasses

Glasses in the compositions (Li₂O)₂₅–(BaO)₂₅–(P₂O₅)_50−x–(V₂O₅)_x (with x=0.5,1.0,1.5,2.0,2.5, and 3.0 mol%) have been prepared by the conventional melt quenching technique. X-ray powder diffractrogram show broad peaks which conforms glassy nature of the sample. Differential scanning calorimetry (DSC) thermograms show characteristic glass transition temperature (T_g) and it increases with increasing substitution of V₂O₅ for P₂O₅. The measured physical parameters like density, refractive index, ionic concentration and electronic polarizability are found to vary linearly with increasing x. Infrared spectra exhibits few bands, which are attributed to (P=O)_AS, (P=O)_S, (V=O), (P–O–P)_AS,P–O–V, (P–O–P)_AS and O–P–O vibrations. The optical absorption spectra of VO²⁺ ions in these glasses show three bands and are assigned to the ²B₂→ ²E,²B₂→ ²B₁ and ²B₂→ ²A₁ transitions. Electron paramagnetic resonance spectra of all the glass samples exhibit resonance signals characteristic of VO²⁺ ions. The values of Spin-Hamiltonian parameters indicate that the VO²⁺ ions are present in octahedral sites with tetragonal compression and belong to C_4V symmetry.