Kinetics and control of liquid-liquid transition

Recently it was revealed that even a single-component liquid can have more than two liquid states. The transition between these liquid states is called "liquid-liquid transition". This phenomenon has attracted a considerable attention because of its counter-intuitive character and the fundamental importance for our understanding of the liquid state of matter. The connection between the liquid-liquid transition and polyamorphism is also an interesting issue. In many cases, liquid-liquid transitions exist in a region which is difficult to access experimentally. Because of this experimental difficulty, the physical nature and kinetics of the transition remains elusive. However, a recent finding of liquid-liquid transition in molecular liquids opens up a possibility to study the kinetics in detail. Here we report the first detailed comparison between experiments and a phenomenological theory for the liquid-liquid transition of a molecular liquid, triphenyl phosphite. Both nucleation-growth-type and spinodal-decomposition-type liquid-liquid transformation are remarkably well reproduced by a two-order-parameter model of liquid that regards the liquid-liquid transition as the cooperative formation of locally favored structures. This may shed new light on the nature and the dynamics of the liquid-liquid transition. We also show evidence that this second order parameter controls the fragility of the liquid. We also discuss a possibility of controlling liquid-liquid transition by spatial confinement. Remaining open questions on the nature of the transition are also discussed.