Klaas Wynne: Phase separation and nucleation: from frustration to control

Ever since it was suggested that the anomalous properties of liquid water could explained by an amorphous to amorphous liquid-liquid transition, the hunt has been on for other examples of such transitions. ¹ Surprisingly, only two other examples of liquid-liquid transitions were found in molecular liquids and even these are highly controversial. I will show that one of these (in n-butanol) is, in fact, more like a liquid-crystal transition but one in which the liquid crystal is not “in between” the liquid and the crystal but instead frustrates the formation of the crystal. ²

However, we are not content to passively observe phase transitions but desire to gain control over the nucleation of new phases. I will show that concentration fluctuations in the neighbourhood of a liquid-liquid critical point can be harnessed by a laser-tweezing potential to induce concentration gradients. ³ A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation through a laser-tweezing potential suggests new ways of manipulating matter.

1     Mosses, J., Syme, C. D. & Wynne, K. Order Parameter of the Liquid–Liquid Transition in a Molecular Liquid. J. Phys. Chem. Lett. 6, 38-43 (2015). https://doi.org/10.1021/jz5022763

2     Syme, C. D., Mosses, J., González Jiménez, M., Shebanova, O., Walton, F. & Wynne, K. Frustration of crystallisation by a liquid–crystal phase. Sci. Rep. 7, 42439 (2017). https://doi.org/10.1038/srep42439

3     Walton, F. & Wynne, K. Control over phase separation and nucleation using a laser-tweezing potential. Nat. Chem. 10, 506-510 (2018). https://doi.org/10.1038/s41557-018-0009-8