the solubility of DHSA in IPA increased and the crystal growth
rate of DHSA decreased. As DHSA crystal propagated, the mixture
became less concentrated and more stable. As the mixture was
less supersaturated, further crystallization occurred less spontaneously.
The programmed temperature pushed the mixture from
the stable phase (below the solubility-saturation curve) at a starting
temperature of 80 ◦C to the metastable- (undercooling) and
unstable-(supercooling, above the supersaturation curve) phases
at final temperatures of 20, 25 and 30 ◦C. At a lower final temperature,
the concentration of DHSA (the solute) in the mixture
was higher than its solubility in comparison to that at a higher
final temperature and thus yielded more DHSA crystals. A similar
observation was reported by Abidin et al. (2009). At a controlled
IPA concentration, more crystals were retained at a lower temperature,
as there were a greater amount of large crystal clusters and a
lesser amount of smaller ‘loose’ and ‘individual’ crystals. It has been
reported that these crystal clusters agglomerated into plate-like
(flaky) forms (Koay et al., 2009).