Banerjee Anirudha, Williams Ian, Azevedo Rodrigo Nery, Helgeson Matthew E, Squires Todd M
Department of Chemical Engineering, University of California, Santa Barbara, CA 93106.
Department of Chemical Engineering, University of California, Santa Barbara, CA 93106
Proc Natl Acad Sci U S A. 2016 Aug 2;113(31):8612-7. doi: 10.1073/pnas.1604743113. Epub 2016 Jul 7.
Equilibrium interactions between particles in aqueous suspensions are limited to distances less than 1 μm. Here, we describe a versatile concept to design and engineer nonequilibrium interactions whose magnitude and direction depends on the surface chemistry of the suspended particles, and whose range may extend over hundreds of microns and last thousands of seconds. The mechanism described here relies on diffusiophoresis, in which suspended particles migrate in response to gradients in solution. Three ingredients are involved: a soluto-inertial "beacon" designed to emit a steady flux of solute over long time scales; suspended particles that migrate in response to the solute flux; and the solute itself, which mediates the interaction. We demonstrate soluto-inertial interactions that extend for nearly half a millimeter and last for tens of minutes, and which are attractive or repulsive, depending on the surface chemistry of the suspended particles. Experiments agree quantitatively with scaling arguments and numerical computations, confirming the basic phenomenon, revealing design strategies, and suggesting a broad set of new possibilities for the manipulation and control of suspended particles.
水悬浮液中粒子间的平衡相互作用仅限于小于1微米的距离。在此，我们描述了一个通用概念，用于设计和构建非平衡相互作用，其大小和方向取决于悬浮粒子的表面化学性质，其作用范围可延伸数百微米并持续数千秒。这里描述的机制依赖于扩散泳，其中悬浮粒子响应溶液中的梯度而迁移。涉及三个要素：一个溶质惯性“信标”，设计用于在长时间尺度上发射稳定的溶质通量；响应溶质通量而迁移的悬浮粒子；以及介导相互作用的溶质本身。我们展示了溶质惯性相互作用，其延伸近半毫米并持续数十分钟，根据悬浮粒子的表面化学性质，这种相互作用可以是吸引性的或排斥性的。实验在数量上与标度论证和数值计算一致，证实了基本现象，揭示了设计策略，并为悬浮粒子的操纵和控制提出了一系列广泛的新可能性。
