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

聚合物复合材料可以由聚合物(想想液体塑料)和非常小的刚性颗粒的混合物组成。这种颗粒的加入可以增强聚合物的性能，并可能改变其官能度。例如，这种复合材料可以变得导电，或者响应于诸如光或热的外部刺激而改变其形状(例如，弯曲)。这可以提供一种从一维或二维结构获得三维形状的强大方法。为了实现这种功能，需要对这种颗粒在聚合物中的位置进行准确的设计。该项目将专注于使用声波(即压力振动)来编程小颗粒的位置和随时间变化的行为，以调整复合聚合物系统的物理响应。该项目将创造新的机会，推动能够应对环境变化的下一代材料的进步。这些材料可用于设计用于生物医学应用的小型软机器人。该奖项将吸引和培训与流体力学、传质、无机和有机材料相关的学科的研究生和本科生。这项研究的内容将用于为K-12学生创建动手活动，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被用来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基于刺激响应聚合物的微型致动器和形状可重构物质的关键障碍。为了克服这些挑战，该项目将通过理解相关的物理、力学和动力学原理，探索表面声波驱动的纳米颗粒在剪切变稀聚合物溶液中时空分布的基本机制，使其能够在交联后发生三维形状变化。本项目将验证这样一个假设，即在表面声波作用下，聚合物流体的剪切变稀行为会影响纳米颗粒在刺激响应型聚合物基质中的局部化程度、空间分布和组装结构。它将进一步评估去除表面声波后纳米颗粒随时间的分解情况，方法是根据聚合物浓度和表面声波诱导的剪切速率来量化聚合物溶液的有效粘度。这种基本的理解将允许在更复杂的图案中进行精确的粒子操作，从而能够形成非传统的组装特征，如螺旋结构。这些成果将有助于理解表面声波驱动纳米颗粒在刺激响应型聚合物基质中时空组装的基本机制，实现亚毫米级的可编程形状重新配置和运动。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.