Influence of preparation pathway on the glass forming ability

The glass forming ability (GFA), i.e. the ease of amorphization of drugs, is mostly investigated using the critical cooling rate upon melt quenching to generate an amorphous product via the thermodynamic pathway. However, amorphous materials can also be prepared via the kinetic pathway by milling. In this case, the time required to generate an amorphous product is called the minimal milling time. This study investigates the correlation of the GFA between these two pathways. Eighteen compounds were chosen and their GFA was investigated by determining the critical cooling rate and the minimal milling time. It was observed that drugs, which turned amorphous upon cooling from the melt at slow cooling rates also had a low minimal milling time and vice versa. It was found that the GFA of the studied set of drugs was inherent and independent of the preparation method. It can be concluded that a drug with low critical cooling rate will also have a low minimal milling time and is thus a good glass former.