The implication of the glass transition in the formation of trehalose/mannitol molecular alloys by ball milling

In this paper, we show the possibility of forming amorphous molecular trehalose/mannitol alloys by two independent routes: the usual thermal quenching of the mixed melts, and the co-milling of the stable crystalline forms at room temperature. However, by quenching the melt, molecular alloys can be obtained for the whole range of mannitol concentration, while by co-milling the possibility of forming the alloy ceases when the glass transition temperature of the alloy approaches the milling temperature. The fraction of mannitol not involved in the alloy then undergoes a polymorphic transformation toward a metastable polymorph which coexists with the alloy. The detailed analysis of all these transformations indicates clearly that the glass transition temperature is a key parameter which drives the "amorphization/polymorphic transformation" duality often detected during the milling of molecular materials. (c) 2007 Elsevier Ltd. All rights reserved.