The importance of relative growth rates in the preponderance of alpha- over gamma-glycine during solution crystallisation has been confirmed. Most surprisingly tailor-made additives drastically accelerated the growth of gamma-glycine--an unexpected and key factor in the polymorphic outcome of glycine crystallisation.

The experimental observation that certain crystal faces do not grow, despite being in contact with supersaturated solution, is a widely reported phenomenon. This concept of a growth 'dead zone' has been known for many years but its origin remains an unresolved problem in crystal growth. Sometimes it seems to be an inherent feature of the solution growth process while at others it appears that an impurity is an essential element for its appearance. Here we review existing data and provide new experimental evidence to confirm the widespread existence of the dead zone across a range of molecular materials. Available crystal growth kinetics are confronted with mechanistic models. Examination of the packing arrangements of appropriate crystal faces suggests that this behavior is linked to molecular scale surface roughness.Supporting information for this article is given via a link at the end of the document. Entry for the Table of Contents FULL PAPERThe 'general' existence of the dead zone has been confirmed and it appears to be related to surface rugosity.

The glycine polymorphs have provided a rich and challenging tapestry for crystal growth and polymorphism studies. In this new contribution we report some preliminary studies of the impact of two ionic surfactants on the morphologies and the competitive crystallisation of the α and γ polymorphs. We find both selective growth inhibition and acceleration combined with fascinating crystal aggregates. The role of both monomeric and micellar forms of the surfactants are explored and discussed in terms of nucleation and crystal growth processes.