Curvature gradient driven assembly of trapped and reconfigurable structures

非技术摘要将微尺度颗粒组织成明确结构的能力是我们设计新的软质可重构材料的核心。 通常，外部静电场或磁场用于引导粒子进入它们可以相互作用并形成结构的位置。这项工作研究了过去没有得到广泛重视或使用的领域。 流体界面上的颗粒变形并增加其周围的界面面积。表面张力和该面积增加的乘积是取决于流体界面的曲率的能量场，因此颗粒沿着曲率梯度移动。 通过这个简单但显著的事实，界面本身的几何形状可以用来指导组装。 在这里，这些领域的研究，以确定新的方法来形成难以形成的结构，通过传统的手段，使新材料的性能进行了探索。研究生和本科生在执行拟议的研究过程中进行培训，包括学生在路易斯·斯托克斯联盟少数民族参与计划，在工程计划和UPENN MRSEC REU程序的推进妇女。开发的新知识将被纳入研究生课程的界面phenomenon.Technical AbstractThis research旨在建立新的战略，直接组装的微米和亚微米尺度的颗粒远远超出通常的紧密堆积的组件。 捕获在流体界面处的颗粒通过毛细作用沿着界面曲率梯度相互作用和迁移。 这些能量驱动与界面曲率场强烈相关的复杂结构的形成，受粒子-粒子相互作用的影响。由于软物质本身是可变形的，这种相互作用是形成可重构、可调组件的自然途径。不同类别的结构进行了研究，使用光学显微镜观察结构，光刻定义的血管模具流体界面和磁性和其他探头扰动的结构，并指导其重新配置。动力学捕获的结构进行了研究，形成胶体单层膜的空隙，致密的区域和定向结构，响应于界面形状的变化。平衡结构的研究，以形成沿沿着界面主轴排列的结构，并研究其界面扰动后的重构。 通过光学显微镜观察结构形成的（动力学）颗粒的形状和尺寸选择的毛细管相互作用的规模，他们激发和他们的能力，形成定向结构与相关的各向异性的结构响应扰动。对于这两个限制，粒子的位置/方向进行比较，并与界面曲率。 观测结果进行比较，以适当的预测，例如，斯托克斯动力学模拟被困结构和蒙特卡罗模拟平衡结构的基础上。

Non-technical AbstratThe ability to organize microscale particles into well-defined structures lies at the heart of our ability to design new soft, reconfigurable materials. Often, external electrostatic or magnetic fields are used to guide particles into positions where they can interact and form structures. This work studies fields that have not been widely appreciated or used in the past. Particles on fluid interfaces deform and increase the area of the interface around them. The product of surface tension and this area increase is an energy field that depends on the curvature of the fluid interface, so particles move along curvature gradients. Through this simple but remarkable fact, the geometry of the interface itself can be used to direct assembly. Here, these fields are studied to identify new ways to form structures difficult to form by conventional means to make new materials whose properties are explored. Graduate and undergraduate students are trained in the course of performing the proposed research, including students in the Louis Stokes Alliance for Minority Participation program, the Advancing Women in Engineering Program and the UPENN MRSEC REU program. New knowledge developed will be incorporated in a graduate course on interfacial phenomena.Technical AbstractThis research seeks to establish new strategies for directed assembly of micron and sub-micron scale particles to go well beyond the usual close packed assemblies. Particle trapped at fluid interfaces interact and migrate along interface curvature gradients via capillarity. These energies drive formation of complex structures strongly correlated with the interface curvature field, influenced by particle-particle interactions. Since soft matter is inherently deformable, such interactions are a natural route to form reconfigurable, tunable assemblies. Different classes of structures are studied using optical microscopy to observe structures, lithographically defined vessels to mold fluid interfaces and magnetic and other probes to perturb the structures and to guide their reconfiguration. Kinetically trapped structures are studied to form colloidal monolayer membranes with voids, dense regions and oriented structures which respond to changes in interface shape. Equilibrated structures are studied to form structures aligned along principle axes of the interfaces and to study their reconfiguration upon interface perturbation. The (dynamics of) structure formation is observed by optical microscopy for particle shapes and sizes selected for the scale of capillary interactions that they excite and their ability to form oriented structures with associated anisotropies in the structural response to perturbation. For both limits, particle positions/ orientations are compared to and correlated with the interface curvature. Observations are compared to appropriate prediction based on, for example, Stokesian Dynamics simulations for trapped structures and Monte Carlo simulations for equilibrated structures.