Induced crystal G phase through intermolecular hydrogen bonding VII. Influence of non-covalent interactions on mesomorphism and crystallization kinetics
M. Srinivasulu et al., Induced crystal G phase through intermolecular hydrogen bonding VII. Influence of non-covalent interactions on mesomorphism and crystallization kinetics, LIQ CRYST, 28(9), 2001, pp. 1321-1329
A series of intermolecular hydrogen bonding complexes, 2,2'-bipyridine : p-
n-alkoxybenzoic acids (BP: nABA) was isolated from liquid crystalline p-n-a
lkoxybenzoic acids (nABA) (where n represents alkoxy carbon numbers, 3 to 1
0 and 12) and a non-mesogen, 2,2'-bipyridine (BP). The thermal and phase be
haviour of these complexes was studied by thermal microscopy and differenti
al scanning calorimetry (DSC). These studies revealed the induction of tilt
ed smectic F and crystal G phases. The structural elucidation pertaining to
the formation of intermolecular hydrogen bonding was carried out by a deta
iled IR spectral investigation. Comparative crystallization kinectic studie
s using DSC, performed on two representative compounds, showed different fo
rms of the crystallization process. The magnitudes of the Avrami exponent n
suggests two different mechanisms operate for individual members leading t
o sporadic three-dimensional growth. Nevertheless, an overall unique mechan
ism is predicted to operate at each crystallization temperature investigate
d, while the Avrami constant b shows a temperature dependence suggesting a
strong influence of alkoxy terminal groups on the rates of nucleation.