Dielectric properties of a strongly polar nematic liquid crystal compound doped with gold nanoparticles

This study focuses on the electrical characteristics of a strongly polar nematic liquid crystal, Hexyloxy-cyanobiphenyl (6OCB), doped with a low concentration (2% by weight) of citrate buffer stabilised gold nanoparticles (GNPs) at low frequencies between 20 Hz and 35 MHz. The doped samples have lower values of nematic–isotropic transition temperature, permittivity (both parallel and perpendicular to the field direction) and dielectric anisotropy; however, relaxation time and activation energy were increased. The observed results could be explained on the basis of weakly anisotropic nature of GNPs and a local rearrangement of liquid crystal molecules surrounding the nanoparticles. Moreover, a complimentary suggestion on a possible change in the dipole–dipole correlation is made to explain the difference in changes (qualitative and quantitative) observed for permittivity of the host nematic liquid crystal doped with GNP. Temperature dependent dielectric relaxation studies indicate an increase in viscosity and potential barrier; and hence a change in strength of inter-molecular and intra-molecular interactions is suggested.     

Theta-point exponent for polymer chain in random media

Using field-theoretic arguments for self-avoiding walks on dilute lattices with site occupation concentrationp, we show that the-point size exponent _p ⁰ of polymer chains remains unchanged for small disorder concentration (p>p _c ). At the percolation thresholdp=p _c , using a Flory-type approximation, we conjecture that _pc ⁰ =5/(d _B +7), whered _B is the percolation backbone dimension. It shows that the upper critical dimensionality for the-point transition atp=p _c shifts to a dimensiond _c >3. We also propose that the-point varies practically linearly withp for 1>pp _c .     

Electric-field mapping of some substituted 3-pyridinecarboxylic acid cardiotonics and the possible structure–activity relationships

Four esters of 5-cyano-1,6-dihydro-6-oxo-3-pyridinecarboxylic acid involving substitutions of methyl, isopropyl, tert-butyl, and phenyl groups at the 2-position, which exhibit varying degrees of cardiotonic activities, have been studied using the electric-field and electrostatic potential mapping techniques. The net charge distributions in the molecules were obtained using the MNDO method. Electric-field mapping has been performed in three-dimension in order to obtain information about the possible structure–activity relationships of these compounds. The results show a prominent electric-field region in the methyl-substituted compound extending from near the oxygen atom O₆ to near the methyl group. This fact and orientation of the electric field in this region, in view of the Erhardt model, may be related to the greater cardiotonic activity of the methyl-substituted molecule in comparison to those of the other molecules of this class. © 1992 John Wiley & Sons, Inc.