Among the seven different forms of (() modafinil, form I is the most stable variety (at whatever the temperature, T), and form III is very close to form I in terms of lattice energy. Under high-energy milling (HEM), every modification converts into a defective form III. The inversion of "stability" between form I and form III is then evidenced when a high-powered mechanical flux of energy is applied. When 3% mass/mass of watersa very poor solvent for this racemic compoundsis introduced in the vials, the same types of experiments lead to defective form I. This study tends to show that whatever the number of polymorphic forms in the temperature, pressure (T, P) space, a single variety exists as a steady state for a given set of HEM parameters.

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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.