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G. Govindaraj

Publications and source records attributed to G. Govindaraj.

2 recordsLinked to original sources

Novel Concept of Non-Debye Dipole Relaxation Processes for the Interpretation of Physical Origin of Dielectric Loss in the Glass Formers, Drugs, Polymers and Plastic Crystals

The physical origin of dielectric loss is shown to be sum of n number of subunits relaxation of a molecule, where n=1,2,3.. For each subunit relaxation, the idea of intermolecular dipole-dipole interactions triggered non-Debye dipole, ($\bf G$)$_{n}$=((1-g$_d$)$\bf G$$_{0}$)$_{n}$, and the ensuing dual dipole ($\bf G$$_{\pm}$)$_n$=($\bf G$$_0$$\pm$$\bf G$)$_n$, relaxation processes is proposed, where $\bf G$$_{-}$=g$_{d}$$\bf G$$_{0}$, $\bf G$$_{+}$=(2-g$_{d}$)$\bf G$$_{0}$, and $\bf G$$_{0}$ is a Debye dipole. Each subunit motion is statistically highly independent process and discriminated by Debye and non-Debye relaxation (NDR) time, where g$_d$ is an exponent 0<g$_d$<1 and signifies interaction strength with a redistribution and conservation of Debye dielectric loss energy. The proposed concept provides a new insight for the NDR and discloses the physical origin of $α$, $β$, $γ$, $δ$ relaxations and excess wing of glass formers, plastic crystals, drugs, etc., with an excellent agreement with experimental results.

cond-mat.soft

Dielectric relaxation and crystallization behaviour of amorphous nilutamide

The molecular mobility of glass and supercooled liquid states of nilutamide has been studied with broadband dielectric spectroscopy for a wide range of temperature and frequency. Besides primary $α$-relaxation an excess wing like secondary relaxation is observed. The temperature dependence of structural $α$-relaxation show non-Arrhenius behaviour, and follows Vogel-Fulcher-Tammann (VFT) empirical formula. The glass transition temperature, T$_{g}$=302K and fragility index, m=76 are obtained from the VFT parameters. The structural $α$-relaxation process is non-Debye with Kohlraush-Williams-Watts stretched exponential $β_{KWW}$=0.76. Secondary relaxation time of nilutamide coincides with the primitive relaxation time calculated from the coupling model. Hence the secondary relaxation process of nilutamide is treated as the Johari-Goldstein (JG) $β$-process, which is the precursor of the structural $α$-process. Recent report on nilutamide indicates the increase of nucleation even below T$_{g}$, however we attributed to the JG $β$-relaxation. During the dielectric measurements amorphous nilutamide recrystallizes. The crystallization of amorphous nilutamide has been studied by the isotherm dielectric measurements at T=326K over a period of time. The crystallization follows Avrami equation and the parameters are obtained.

cond-mat.soft