The Fluid to Solid Transitions in Soft Materials

软材料通常是粘弹性的，表现出流体和固体的特性。 通常一种行为占主导地位，并且材料主要是流体或固体;然而，这可能敏感地取决于测量。 例如，玻璃状材料在通常测量的频率下可以是固体，但在非常低或非常高的频率下可以是流体。 因此，类流体和类固体行为之间的过渡可能非常微妙，但它可以提供对行为的深入了解。 这种类流体和类固体行为之间的过渡是这里提出的工作的首要主题。 建议的实验包括调查胶体晶体，玻璃和凝胶与共聚焦显微镜看个别粒子，散射测量平均效果，和流变学测量散装效果。 一个剪切细胞将建立一个共聚焦显微镜探测粒子的运动时，受到剪切，激光镊子将被用来探测局部扰动的结构。 这些实验将提供对软质材料中重要的流体到固体转变的深入了解。许多在自然界和技术中很重要的材料都具有双重特性--当从管中挤出或涂抹在牙齿上时，它们既具有固体状又具有流体状，但当涂抹在牙刷上时，它们保持固体的形状和形式。 本研究将探讨具有这种双重性质的广泛类别的材料的性质，并将集中在从流体状行为到固体状行为的转变。 这项工作将寻找可以在广泛的材料类别中描述这种行为的一般特征，并将调查导致这种行为的材料的结构特性。 该研究将通过与行业的互动得到高度利用，确保除了具有根本重要性的问题外，还解决了具有实际和技术重要性的问题。 此外，研究将与教育工作相结合，通过研讨会和讲习班系列，提高当地科学家的研究人员社区，通过项目，将从事本科生和高中教师的夏季研究，并通过设计一个新的课程，探索科学研究的创造力。

Soft materials are often viscoelastic, displaying characteristics of both a fluid and a solid. Often one behavior dominates, and the material is dominantly either a fluid or a solid; however, this can depend sensitively on the measurement. For example, a glassy material can be solid at frequencies typically measured, but fluid at very low or very high frequencies. Thus, the transition between fluid-like and solid-like behavior can be quite subtle, yet it can provide great insight into the behavior can be quite subtle, yet it can provide great insight into the behavior of the material. This transition between fluid-like and solid-like behavior is the overarching theme of the work proposed here. Experiments proposed include investigation of colloidal crystals, glasses and gels with confocal microscopy to look at individual particles, scattering to measure average effects, and rheology to measure bulk effects. A shear cell will be built for a confocal microscope to probe the motion of particles when subjected to shear, and laser tweezers will be used to probe local perturbations of structure. These experiments will provide insight into important fluid to solid transitions in soft materials.Many materials that are important in nature and in technology have a dual character they have both solid-like and fluid-like when squeezed from the tube or smeared on teeth, but maintains its shape and form like a solid when spread on a toothbrush. This research will investigate the nature of a wide class of materials that have this dual character, and will focus on the transformation from the fluid-like behavior to the solid-like behavior. The work will search for general features that can describe this behavior in wide classes of materials, and will investigate the structural properties of the materials that cause this behavior. The research will be highly leveraged through interactions with industry, ensuring that problems of practical and technological importance and addressed, in addition to problems of fundamental importance. In addition, the research will be coupled with educational efforts, through seminar and workshop series that enhance the researcher community for scientists in the local area, through projects that will engage undergraduate students and high school teachers for summer research, and through the design of a new course to explore creativity in scientific research.