NSF-DFG Confine: Chemically-induced phoretic flow, or how to turn a curtain of light into virtual micro-fluidic boundaries

该奖项是德国波茨坦大学的一个实验小组与加州理工学院的一个理论小组合作，研究受限几何形状中小颗粒的光激活化学诱导流动。通过施加简单的光学刺激，可以以前所未有的控制和精度水平操纵单个和批量的胶体颗粒。该研究旨在为“虚拟”微流体设备奠定基础，该设备利用光激活流动模式产生的软边界，其强度和位置是可调的，并允许操纵和控制胶体级物体。该研究在细胞分选、DNA操作和胶体基材料组装等方面具有潜在的技术应用。该奖项的合作性质将有助于拓宽研究生的视野，因为他们与来自不同国家和背景的其他人合作，这在这个全球联系但脆弱的世界中越来越重要。这个奖项建立在最近发现的光驱动扩散现象的基础上，并将其扩展-一种渗透作用，其中化学表面活性剂的疏水性被光照改变，并产生渗透压梯度，该渗透压梯度驱动流体和颗粒议案这项研究的目的是对扩散泳流有一个基本的了解;也就是说，运动如何取决于化学浓度、离子强度、光强度等基本物理性质，以及颗粒之间和与限制基底的流体动力学相互作用。三种不同的过程来操纵邻近边界的粒子系综：（i）导致粒子聚集的光强度的全球空间模式（ii）多孔（源）颗粒之间的自生排斥，所述多孔（源）颗粒结晶并增强被捕获的被动胶体的运动;以及（iii）自推进的Janus粒子，其速度和持续时间可以动态地控制。理论表明，光诱导的流动剖面，尽管是非平衡现象，可以用平衡的化学“溶质势”来表示，这表明了对结晶，相分离等的有趣类比。该奖项是关于一个独特的非平衡系统的理论和实验的紧密结合，该系统触及了许多光驱动粒子动力学和流体力学的前沿问题，如颗粒混合物中的分离动力学和动态波动的受限几何形状中主动自推进颗粒的运动。该项目通过“受限空间中的化学和运输”获得（NSF-DFG限制）”机会，一项涉及美国国家科学基金会和德国研究共同体（DFG）的合作征集活动该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is a collaboration between an experimental group at the University of Potsdam in Germany and a theoretical group at the California Institute of Technology to study the light-activated chemically induced flow of small particles in confined geometries. By applying simple optical stimuli, colloidal particles, both individually and in bulk, can be manipulated with unprecedented levels of control and precision. The research aims to establish the foundation for ‘virtual’ microfluidic devices that utilize soft boundaries generated from light-activated flow patterns whose strength and location are tunable and allow the manipulation and control of colloidal-scale objects. The research has potential technological applications in, for example, cell sorting, DNA manipulation, and the assembly of colloidal-based materials. The collaborative nature of the award will help broaden the horizon of research students as they work with others from different countries and backgrounds, which is increasingly important in this globally connected but fragile world.This award builds on and extends the recently discovered phenomenon of light-driven diffusion-osmosis in which a chemical surfactant’s hydrophobicity is altered by illumination and generates an osmotic pressure gradient that drives fluid and particle motion. The study is aimed at a fundamental understanding of the diffusiophoretic flow; that is, how the motion depends on the basic physical properties of chemical concentration, ionic strength, light intensity, etc., as well as the hydrodynamic interactions among particles and with the confining substrate. Three different processes to manipulate ensembles of particles adjacent to a boundary are investigated: (i) global spatial patterns of light intensity that cause particles to accumulate in (vacate from) regions of low (high) solute concentration, allowing one to ‘paint’ with colloids; (ii) self-generated repulsion between porous (source) particles that crystalize and enhance motion of trapped passive colloids; and (iii) self-propelled Janus particles whose speed and duration can be dynamically controlled. Theory suggests that the light-induced flow profiles, despite being non-equilibrium phenomena, can be expressed in terms of an equilibrium-like chemical ‘solute potential,’ which suggests intriguing analogies to crystallization, phase separation, etc. The award is a close alignment of theory and experiment regarding a unique non-equilibrium system that touches upon many cutting-edge problems of phoretically-driven particle dynamics and hydrodynamics, such as segregation dynamics in mixtures of particles and the motion of active self-propelled particles in dynamically fluctuating confined geometries.This project was awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.