| dc.description.abstract | Dielectric relaxation studies of some potential
systems involving molecular interaction particularly
intermolecular and/or intramolecular hydrogen bonding
as well as of some related molecules have been carried out
in which atactic polystyrene and several other glass-forming
media, namely, glassy o-terphenyl, bis(m-(m-phenoxy phenoxy)-
phenyl) ether (commonly known as Santovac®), cis-decalin
and carbontetrachloride were utilized as solvents.
Sample preparations and the dielectric measurements by the
use of a General Radio 1621 Precision Capacitance Measurement
system with appropriate temperature controllable cells have been described. The glass transition temperature
(T[subscript g]) measurements using the Glass Transition Temperature
Measurement Apparatus have also been described. The experimental
data as a function of frequency at different temperatures
were subject to analysis by a series of computer
programmes written in the APL language. The activation
energy barriers opposing the dielectric relaxation processes
were obtained by the application of the Eyring rate equation.
Different types of polar, fairly spherical, rigid
molecules have been studied mainly to provide sources of relaxation data and activation parameters for comparison
with those of flexible molecules of analogous size. The
molecular relaxation parameters for these rigid molecules
were found to depend on the size, shape and volume of the
molecules and the nature of the dispersion medium. The
solute concentration has a negligible effect on the molecular
relaxaton parameters but it influences the dielectric loss
factor, e", significantly. At lower .concentration,
the dielectric loss factor increases linearly with the solute
concentration and at higher concentration after a certain
point it begins to decrease towards the value observed for
the pure molecule. This is accounted for by intermolecular
interactions.
Of the flexible molecules, a variety of some
simple almost spherical alcohols, and some long-chain
aliphatic normal alcohols and thiols have been studied in
different g1ass-forming media. In the usual concentration
range of polystyrene matrices ('^5% by.wt.) no evidence of
intermoleculr hydrogen bonding was found in simple alcohols,
long-chain alcohols and thiols. For simple alcohols
only molecular relaxation was observed. Long-chain alcohols
and thiols exhibited two relaxation processes. The lower
temperature processes were attributed to segmental rotation
involving CH[subscript 2]X movement while the higher temperatures were respective molecular rotation.. Relaxation due to hydroxyl
group rotation was not found in any case. At higher
concentration molecular relaxation followed by hydrogen
bond breaking and in some cases relaxation for hydrogen
bonded species was observed in G.O.T.P., carbontetrachloride
and polystyrene. As in the case of rigid molecules, similar
effects of solute concentration upon the molecular relaxation
parameters and dielectric loss factor, e[symbol], have been observed
for simple alcohols in carbontetrachloride.
A wide variety of potentially intramolecular
hydrogen bonded substituted phenols has been examined in
cis-decalin, G.O.T.P. and Santovac® and in most cases,
hydroxyl group relaxation was observed. The relaxation
parameters for hydroxyl group rotation were found to be
significantly influenced by the strength of the intramolecular
hydrogen bond but it was virtually independent of the nature
of the dispersion medium as well as the nature of the
substituent at the para-position of the ring. No evidence
for proton tunneling was detected in these molecules. | |
