Department of Fundamental Engineering, Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, Japan
Proc Natl Acad Sci U S A. 2020 Mar 3;117(9):4471-4479. doi: 10.1073/pnas.1911544117. Epub 2020 Feb 12.
Liquid-liquid transition (LLT) is an unconventional transition between two liquid states in a single-component system. This phenomenon has recently attracted considerable attention not only because of its counterintuitive nature but also since it is crucial for our fundamental understanding of the liquid state. However, its physical understanding has remained elusive, particularly of the critical dynamics and phase-ordering kinetics. So far, the hydrodynamic degree of freedom, which is the most intrinsic kinetic feature of liquids, has been neglected in its theoretical description. Here we develop a Ginzburg-Landau-type kinetic theory of LLT taking it into account, based on a two-order parameter model. We examine slow critical fluctuations of the nonconserved order parameter coupled to the hydrodynamic degree of freedom in equilibrium. We also study the nonequilibrium process of LLT. We show both analytically and numerically that domain growth becomes faster (slower), depending upon the density decrease (increase) upon the transition, as a consequence of hydrodynamic flow induced by the density change. The coupling between nonconserved order parameter and hydrodynamic interaction results in anomalous domain growth in both nucleation-growth-type and spinodal-decomposition-type LLT. Our study highlights the characteristic features of hydrodynamic fluctuations and phase ordering during LLT under complex interplay among conserved and nonconserved order parameters and the hydrodynamic transport intrinsic to the liquid state.
液-液相变 (LLT) 是单一组分系统中两种液相之间的非常规转变。这种现象最近引起了相当大的关注，不仅因为它违反直觉，而且因为它对我们对液相的基本理解至关重要。然而，其物理理解仍然难以捉摸，特别是对于临界动力学和相序动力学。到目前为止，在其理论描述中忽略了液体最内在的动力学特征——流体动力学自由度。在这里，我们基于双参数模型，考虑到这一点，发展了一种液-液相变的吉布斯-朗道型动理学理论。我们研究了平衡时非守恒序参量与流体动力学自由度的慢临界涨落。我们还研究了液-液相变的非平衡过程。我们从理论和数值上都表明，由于密度变化引起的流体流动，畴的生长在相变时密度降低（增加）时会变快（慢）。非守恒序参量与流体相互作用的耦合导致成核生长型和旋节分解型 LLT 中畴的异常生长。我们的研究强调了在保守和非保守序参量以及液体固有流体输运之间复杂相互作用下，液-液相变过程中流体动力学涨落和相序的特征。
