Center for Soft Matter Research, Department of Physics, New York University, New York, New York 10003, USA.
Debye Institute for Nanomaterials Science, Utrecht University, 3584 Utrecht, The Netherlands.
Phys Rev E. 2017 Sep;96(3-1):032607. doi: 10.1103/PhysRevE.96.032607. Epub 2017 Sep 15.
Concentration gradients play a critical role in embryogenesis, bacterial locomotion, as well as the motility of active particles. Particles develop concentration profiles around them by dissolution, adsorption, or the reactivity of surface species. These gradients change the surface energy of the particles, driving both their self-propulsion and governing their interactions. Here, we uncover a regime in which solute gradients mediate interactions between slowly dissolving droplets without causing autophoresis. This decoupling allows us to directly measure the steady-state, repulsive force, which scales with interparticle distance as F∼1/r^{2}. Our results show that the dissolution process is diffusion rather than reaction rate limited, and the theoretical model captures the dependence of the interactions on droplet size and solute concentration, using a single fit parameter, l=16±3nm, which corresponds to the length scale of a swollen micelle. Our results shed light on the out-of-equilibrium behavior of particles with surface reactivity.
浓度梯度在胚胎发生、细菌运动以及活性粒子的运动中起着关键作用。粒子通过溶解、吸附或表面物种的反应在其周围形成浓度分布。这些梯度改变了粒子的表面能，驱动它们的自推进并控制它们的相互作用。在这里，我们揭示了一个区域，在这个区域中，溶质梯度在不引起自泳的情况下介导缓慢溶解液滴之间的相互作用。这种解耦使我们能够直接测量稳态、排斥力，其与粒子间距离的比例为 F∼1/r^{2}。我们的结果表明，溶解过程受扩散控制，而不是反应速率控制，并且理论模型使用单个拟合参数 l=16±3nm（对应于溶胀胶束的长度尺度），捕捉了相互作用对液滴大小和溶质浓度的依赖性。我们的结果揭示了具有表面反应性的粒子在非平衡状态下的行为。
