Feldmann David, Arya Pooja, Molotilin Taras Y, Lomadze Nino, Kopyshev Alexey, Vinogradova Olga I, Santer Svetlana A
Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany.
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31 Leninsky Prospect, 119071 Moscow, Russia.
Langmuir. 2020 Jun 30;36(25):6994-7004. doi: 10.1021/acs.langmuir.9b03270. Epub 2020 Mar 10.
The repulsive surface forces, such as electrostatic or steric, acting between particles explain why they remain well separated in aqueous electrolyte solutions and are responsible for the stability of colloidal dispersions. However, the effective range of these interactions is always well below hundreds of nanometers and typically can be controlled by advanced manipulations such as tuning the electrolyte concentration or modifying the particle surface or, in some more specific cases, via subjecting the suspension to an external electric or magnetic field. Here we employ solutions with small additives of a photosensitive ionic surfactant to investigate if a repulsive interaction of microsized particles sedimented at the solid surface can be remotely controlled simply by illuminating it with an appropriate wavelength. We show that interactions of conventional impermeable particles remain practically unaffected by light, but, in contrast, for porous particles, we observe a long-range repulsion, several orders of magnitude longer than any conceivable equilibrium surface force. This repulsion emerges due to the diffusio-osmotic flow generated near the porous particles that in this scenario are playing a role of micropumps. The diffusio-osmotic repulsion of porous particles can be used for a remote control of their two-dimensional assemblies at the solid wall, and in particular, we demonstrate that by simply using two different illumination wavelengths it is possible to reversibly switch the state of porous particle dispersion from densely packed surface aggregates to a periodic lattice of particles separated by distances on the order of tens of micrometers.
粒子之间存在的排斥性表面力，如静电力或空间位阻力，解释了为何它们在水性电解质溶液中能保持良好分离状态，并且是胶体分散体系稳定性的成因。然而，这些相互作用的有效范围总是远低于数百纳米，通常可以通过诸如调节电解质浓度、修饰粒子表面等先进操作来控制，或者在某些更特殊的情况下，通过对悬浮液施加外部电场或磁场来控制。在此，我们使用添加了少量光敏离子表面活性剂的溶液，来研究沉积在固体表面的微米级粒子之间的排斥相互作用是否能通过用适当波长的光照射来远程控制。我们发现，传统的不可渗透粒子之间的相互作用实际上不受光的影响，但是，相比之下，对于多孔粒子，我们观察到一种长程排斥力，其作用范围比任何可想象的平衡表面力都要长几个数量级。这种排斥力是由于在多孔粒子附近产生的扩散渗透流而出现的，在这种情况下，多孔粒子起到了微型泵的作用。多孔粒子的扩散渗透排斥力可用于远程控制它们在固体壁上的二维组装，特别是，我们证明了通过简单地使用两种不同的光照波长，就有可能将多孔粒子分散体的状态从紧密堆积的表面聚集体可逆地切换为间距在几十微米量级的粒子周期性晶格。
