Crystallization kinetics study on higher homologues of benzylidene aniline compounds: impact of phase variant on nucleation process

Abstract

A systematic kinetic study leading to the crystallization process from the kinetophases (which occur prior to crystal phase) smectic B, crystal G and smectic F is performed on representative compounds of the homologous series p-phenylbenzylidene-p¾ -alkylanilines (PBnA) and p-n-alkoxybenzylidene-p¾ -alkylanilines (nO.m) these compounds are p-phenylbenzylidene-p¾ -nonylaniline ( PB9A), p-phenylbenzylidene-p¾ -tetradecylaniline ( PB14A), p-n-pentadecyloxybenzylidenep¾ -tetradecylaniline (15O.14) and p-n-octadecyloxybenzylidene-p¾ -nonylaniline (18O.9). The molecular mechanism and dimensionality in crystal growth from the kineto phases are computed from the Avrami equation, while the characteristic crystalline time (t*) at each crystallization temperature is deduced from the individual plots of log t vs. DH. The low magnitudes of the dimensionality parameter n infers the occurrence of diVusion-controlled transformations leading to the formation of plates or needles of nite size possessing impinged edges. The degree of variation in the value of n at each crystallization temperature also reveals the existence of an independent nucleation mechanism for any individual member of the series. The in uence of the terminal alkyl chain lengths on the rate of crystallization is determined from a comparative study with the reported analogous compounds.

Inter hydrogen bonded complexes of hexadecylaniline and alkoxy benzoic acids: a study of crystallization kinetics

“…A plot of heats of melting of the mesomorphic phase, viz. the log of annealing time for different crystallization temperatures of 16A+12BA is depicted in figure 5 These plots have an identical shape, apart from the shift in the log t axis suggesting the limitations of the rate of crystallization kinetics [14,15]. Furthermore, simultaneous measurement of the heats of melting of the smectic G endotherm with time shows, without ambiguity, that the affective beginning and end of the crystal formation process is uniform and unaltered.…”

“…Such a master curve strongly suggests that the same mechanism operates for crystallization from the smectic G to crystal for both the complexes. As expected [14,15], the overall crystallization rate is controlled by a nucleation rate influencing the rate of growth of domains; this is a function of the degree of super cooling and the starting smectic mesophase. Similar experimental studies are carried out for measurement of crystallization kinetics of the other compound (16A+11BA) of this homologous series.…”

The Influence of the Position of Oxygen on the Phase Behaviour of Benzylidene Anilines

“…The N(p-n-alkoxybenzylidene)-p-n-alkylanilines, popularly known as nO.m of the schiff bases, constitute a series of compounds exhibiting rich polymeromorphism [7,8]. The present preliminary communication presents investigations on schiff bases with the oxygen on either side (nO.m or n.Om), on both sides (nO.Om), or in the absence of oxygen (n.m).…”