Investigation of crystallisation inhibitors through molecular dynamics simulation

The main objective of this study is to contribute towards the understanding of the vitrification process in multicomponent systems. In particular, the aim was to gain a better understanding of how additives inhibit crystallisation and thus promote glass formation. To this end, two very different glass formers were studied: the first was a colloidal suspension that is often used as a model system to study vitrification, and the second was a trehalose solution that has more biological interest. Both glass formers were studied using molecular dynamics simulation as it is a powerful technique that can complement experiment, and allows the determination of properties that may be quite difficult to determine experimentally. By first studying the system without the additives, and then comparing to when the additives are present, a potential mechanism for crystallisation inhibition was observed. The results demonstrate that a key predictor of crystallisation inhibition in both colloidal suspensions and trehalose solutions can be found in the behaviour of the interdiffusion coefficients. The interdiffusion coefficients are related to a multicomponent systems ability to make compositional changes that are needed after a quench for the local stoichiometry to match the equilibrium crystal. It was found that if the value of the interdiffusion coefficient is negligible, this indicated that compositional changes could not occur, and so a long-lived metastable glassy state forms. This was observed in both glass forming systems studied and therefore points to an underlying mechanism that links the interdiffusion process with glass formation. This study supplies evidence of this link, and points out the importance of compositional relaxation in vitrification of multicomponent systems and the need to study the collective properties, rather than just single particle properties, when studying vitrification.<br>