Center for Soft Matter Research, Department of Physics, New York University, New York, NY 10003.
Debye Institute for Nanomaterials Science, Utrecht University, Utrecht 3584, Netherlands.
Proc Natl Acad Sci U S A. 2018 Apr 3;115(14):3599-3604. doi: 10.1073/pnas.1716330115. Epub 2018 Mar 21.
Miscible liquids can phase separate in response to a composition change. In bulk fluids, the demixing begins on molecular-length scales, which coarsen into macroscopic phases. By contrast, confining a mixture in microfluidic droplets causes sequential phase separation bursts, which self-organize into rings of oil and water to make multilayered emulsions. The spacing in these nonequilibrium patterns is self-similar and scale-free over a range of droplet sizes. We develop a modified Cahn-Hilliard model, in which an immiscibility front with stretched exponential dynamics quantitatively predicts the spacing of the layers. In addition, a scaling law predicts the lifetime of each layer, giving rise to a stepwise release of inner droplets. Analogously, in long rectangular capillaries, a diffusive front yields large-scale oil and water stripes on the time scale of hours. The same theory relates their characteristic length scale to the speed of the front and the rate of mass transport. Control over liquid-liquid phase separation into large-scale patterns finds potential material applications in living cells, encapsulation, particulate design, and surface patterning.
可混溶液体可以响应组成变化而发生相分离。在体相流体中，分相始于分子长度尺度，然后粗化形成宏观相。相比之下，将混合物限制在微流体液滴中会导致连续的相分离爆发，这些爆发自组织成油和水的环，从而形成多层乳液。这些非平衡模式的间距在一系列液滴尺寸上具有自相似性和无标度性。我们开发了一种改进的 Cahn-Hilliard 模型，其中具有拉伸指数动力学的不混溶性前沿定量预测了层的间距。此外，标度定律预测了每个层的寿命，从而导致内部液滴的分步释放。类似地，在长矩形毛细管中，扩散前沿在数小时的时间尺度上产生大尺度的油和水条纹。同样的理论将它们的特征长度尺度与前沿速度和质量传输速率联系起来。控制液体-液体相分离成大图案在活细胞、封装、颗粒设计和表面图案化等方面具有潜在的材料应用。
