Enabling new microactuation materials through understanding the influence of shear-dependent viscosities on acoustic field-driven assembly of particles

聚合物复合材料可能由聚合物（想象一下液体塑料）和非常小的刚性颗粒的混合物组成。添加此类颗粒可以增强聚合物性能并可以改变其功能。例如，此类复合材料可以变得导电，或者响应于光或热等外部刺激而改变其形状（例如弯曲）。这可以提供一种强大的方法来从一维或二维结构获得三维形状。为了实现此类功能，需要精确设计此类颗粒在聚合物中的位置。该项目将重点关注使用声波（即压力振动）对小颗粒的位置和时间相关行为进行编程，以调整复合聚合物系统的物理响应。该项目将为开发能够应对环境变化的下一代材料创造新的机会。这些材料可用于设计生物医学应用的小型软机器人。该奖项将吸引和培训流体力学、传质以及无机和有机材料相关学科的研究生和本科生。这项研究的内容将用于为 K-12 学生创建实践活动，并与舰队科学中心合作教育公众。加州大学圣地亚哥分校现有的夏季研究项目将用于吸引女性和代表性不足的少数族裔，以促进 STEM 的多样性和包容性。在微米或纳米尺度上操纵功能纳米颗粒的空间分布和组装结构被认为是制造和设计微型刺激响应聚合物致动器和形状可重构物质的关键障碍。为了克服这些挑战，该项目将通过了解物理、力学和动力学的相关原理，探索剪切稀化聚合物溶液中纳米粒子在交联后能够进行三维形状转变的表面声波驱动时空分布的基本机制。该项目将测试以下假设：聚合物流体的剪切稀化行为会影响表面声波下刺激响应聚合物基质内纳米颗粒的定位程度、空间分布和组装结构。它将通过根据聚合物浓度和表面声波引起的剪切速率量化聚合物溶液的有效粘度，进一步评估去除表面声波后纳米颗粒随时间的分解。这种基本的理解将允许以更复杂的模式进行精确的粒子操纵，从而能够形成非常规的组装特征，如螺旋结构。这些成果将有助于理解刺激响应聚合物基质中表面声波驱动的纳米颗粒时空组装的基本机制，从而实现亚毫米尺度的可编程形状重构和运动。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Polymer composites may consist of mixture of a polymer (think of a liquid plastic) and very small rigid particles. The addition of such particles can enhance polymer properties and could change their functionality. For example, such composites can become electrically conductive, or change their shape (e.g., bend) in response to external stimuli such as light or heat. This could provide a powerful approach to achieve three-dimensional shapes from one or two-dimensional structures. To achieve such functionalities, an accurate design of the location of such particles in the polymer is required. This project will focus on using sound waves (i.e., pressure vibrations) to program the location and time-dependent behavior of small particles to tune the physical response of composite polymeric systems. This project will create new opportunities leading to the advancement of next-generation materials that can respond to changes in the environment. These materials can be used in designing small-scale soft robots for biomedical applications. This award will engage and train graduate and undergraduate students in subjects related to fluid mechanics, mass transfer, and inorganic and organic materials. Elements of this research will be used to create hands-on activities for K-12 students and to educate the public in collaboration with the Fleet Science Center. Existing summer research programs at the University of California San Diego will be leveraged to engage women and underrepresented minorities to promote diversity and inclusion in STEM.Manipulating the spatial distribution and assembled structure of functional nanoparticles at the micro- or nanoscale is recognized as a critical barrier to the fabrication and design of miniaturized stimuli-responsive polymer-based actuators and shape reconfigurable matter. To overcome such challenges, this project will explore the fundamental mechanism of surface acoustic wave-driven spatiotemporal distributions of nanoparticles in shear-thinning polymer solutions capable of three-dimensional shape transformation after crosslinking by understanding associated principles in physics, mechanics, and dynamics. This project will test the hypothesis that shear-thinning behaviors of polymeric fluids affect the degree of localization, the spatial distribution, and assembled structures of nanoparticles within stimuli-responsive polymer matrices under surface acoustic waves. It will further assess the time-dependent disassembly of nanoparticles after removal of surface acoustic waves by quantifying the effective viscosity of polymeric solutions in terms of polymer concentrations and surface acoustic wave-induced shear rates. This fundamental understanding will allow precise particle manipulation in more complex patterns, thereby enabling the formation of unconventional assembled features like helical structures. These outcomes will contribute to understanding the fundamental mechanism of surface acoustic wave-driven spatiotemporal assembly of nanoparticles in stimuli-responsive polymer matrices, enabling programmable shape reconfiguration and motion at the sub-mm scale.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.