Active Surface Agents: Enhanced Transport by Active Colloids at Fluid Interfaces

活性胶体是微米级的自推进物体。它们聚集在界面附近，为界面工程带来了很大程度上尚未开发的自由度。在这里，将研究活性胶体运动，以开发这些对象作为活性表面活性剂。这些试剂可以改善化学过程的混合，并可能导致新的包埋和释放方法。此外，它们在微型机器人等新技术领域也很重要，在这些领域，小物体执行移动货物或释放信号等任务。活性胶体领域的灵感来自于可移动的细菌，这种细菌可以以非常快的速度移动，通常在一秒钟内移动的距离比它们的大小大十倍。也有合成的活性胶体。一个重要的例子是带有铂补丁的聚合物微珠，它与过氧化氢等常见化学物质发生反应，从而推动它们的运动。无活性的普通胶体用于在不混合的流体之间的流体界面形成有组织的结构，以稳定水包油乳状液，广泛用于在个人护理产品中将油性物质包裹在水中，并用于配制药物。流体界面是化学反应和分离的特殊环境。例如，如果在流体界面上存在催化剂，油相中的试剂可能会形成更倾向于水相的产物。这有利于绿色工艺中的反应和分离。创新可以产生经济和社会影响。此外，这项研究将促进科学技术工程和数学教育，包括博士生和本科生研究人员的培训，并作为界面现象课程的课程材料。拟议研究的结果将在外联活动中介绍，以吸引不同背景的学生进入工程学。此外，研究成果将以示范形式向公众传达，并将以细菌作为模型系统。这项研究将开发一个通用框架，以确定所需的活性表面活性剂属性，包括轨迹类型、推进强度和表面密度，以生成所需的活性界面层。研究结果将为促进采用活性胶体层的乳状液、液膜或其他多相体系的界面混合奠定基础。所有活性胶体都遵循相似的流体力学描述，这一点将在本研究中展开。活性胶体聚集在界面附近，可以在界面附近游泳，通过水动力相互作用被捕获，或者可以在附着状态下游泳，其复杂的轨迹在形式和时空含义上都与散装的不同。这项研究将开发一个个体游泳者在界面上和界面附近的响应库，以利用实验和理论来了解他们的个体行为。这项研究将探索界面上的运动是如何传播到邻近的流体中的。通过了解这些影响，可以建立新的有源接口设计规则，以增强多相系统中的传输。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Active colloids are micron-scale self-propelled objects. They accumulate near interfaces, bringing as yet largely untapped degrees of freedom to interfacial engineering. Here, active colloid motion will be studied to develop these objects as Active Surface Agents. These agents can improve mixing for chemical processes, and can lead to new encapsulation and release methods. Furthermore, they are important in new technological spaces like micro-robotics, where small objects perform tasks like moving cargo or releasing a signal. The field of active colloids is inspired by motile bacteria, which can move at extraordinary rates, typically over distances ten times greater than their size in a second. There are also synthetic active colloids. An important example is a polymer micron bead with a platinum patch which reacts with common chemicals like hydrogen peroxide, which fuels their motion. Plain colloids, absent activity, are used to form organized structures at fluid interfaces between fluids that do not mix to stabilize oil in water emulsions, widely used to encapsulate oily substances in water in personal care products and to formulate pharmaceuticals. Fluid interfaces are special environments for chemical reaction and separation. For example, if catalysts are present at fluid interfaces, reagents in the oil phase can form products that prefer the water phase. This facilitates reaction and separation in green processes. Innovation can have economic and social impact. Furthermore, this research will advance Sciences Technology Engineering and Mathematics education, including doctoral student and undergraduate researcher training, and as course material in the Interfacial Phenomena course. The outcome of the proposed research will be presented in outreach activities to attract students from diverse backgrounds to engineering. Furthermore, research findings will be conveyed in demonstrations for the public.Bacteria will be used as a model system. This research will develop a general framework to identify desired active surface agent properties including trajectory type, propulsion strength, and surface density to generate a desired active interfacial layer. The results will lay the ground work to promote mixing at interfaces of emulsions or of thin liquid films or other multi-phase system using active colloidal layers. All active colloids obey similar hydrodynamic descriptions, which this research will develop. Active colloids accumulate near interfaces and can swim adjacent to them, trapped via hydrodynamic interactions, or can swim in an adhered state with complex trajectories that differ from those in bulk in both form and spatio-temporal implications. This research will develop a library of responses of individual swimmers on and near interfaces to understand their individual behaviors using experiment and theory. This research will probe how motion in the interface, a two dimensional active sheet, propagates into the adjacent fluids. By understanding these implications, new design rules for active interfaces can be established to enhance transport in multiphase systems.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.