Survival of the fittest polymorph: How fast nucleater can lose to fast grower

Controlling the crystallization of a liquid able to yield multiple polymorphs is often assumed to be a matter of controlling the initial nucleation. Recent studies found that this view is flawed because an early nucleating polymorph can nucleate another, faster-growing polymorph. We review how the phenomenon is controlled by thermodynamic and kinetic factors and how it can aid the discovery of new polymorphs. The selective crystallization of a polymorph depends not only on the initial nucleation but also on the cross-nucleation between polymorphs and the relative growth rates of polymorphs. © The Royal Society of Chemistry.