Simplification of the landscape under high energy milling of molecular solids exhibiting polymorphism

Abstract
Polymorphism is of high occurrence among molecular solids quite often the number of polymorphs exceeds 3 – 4.Several studies have shown that under high energy milling if Tg < Tmilling there is a simplification of the landscape. That is to say for a given milling intensity, whatever the number of polymorphs existing without mechanical stress, a single polymorph corresponds to the steady state. By changing the milling intensity or the composition of the medium (wet milling for instance) a different variety might be accessible. This solid phase can be: the stable thermodynamic form, a metastable thermodynamic form, a dynamic new metastable form, a solvate, a co-crystal, etc. It is only under special conditions of intensity and composition that two polymorphs can co-exist as dual inter-converting steady states.