Structural transitions, energetics, and folding pathways of colloidal clusters

*技术摘要*胶体团簇的结构和转变可能揭示控制块体现象的局部机制，如成核和结构停滞。这样的簇也是理解自组装路径的有用模型系统。这项实验计划将研究由6-30个粒子组成的三维胶体簇，这些粒子通过弱相互作用如耗尽或DNA介导的结合而聚集在一起。一种先进的成像方法-数字全息显微镜将被用来测量星团中每个粒子的位置和运动，时间分辨率为亚毫秒，在所有三个维度上都有10纳米的精度。这项技术使得能够详细地、定量地研究团簇的基态、平衡结构转变和拓扑转变。结果将被比较并用作能量格局计算的输入，主要目标是了解相变和非平衡现象如何随着系统规模的增加而出现。该项目将培养软物质物理和应用光学方面的研究生和本科生。一个推广和教育项目将把20-40名来自剑桥和波士顿地区公立学校的高中物理学生带到哈佛大学，参加一系列基于发现的关于波、光学和全息术的实验室。*非技术摘要*该奖项支持对称为团簇的不寻常材料的实验研究，有时被称为“中间物质状态”。与我们日常生活中遇到的物质的常见状态--气体、液体和固体--相比，星系团的原子或粒子数量要少得多。因为它们不像普通物质那样复杂，所以原则上更容易理解。研究这些星团如何随着时间和外力的存在而改变其形状，可能有助于解决材料科学中长期存在的挑战，例如晶体是如何形成的，以及为什么它们有时会形成被称为玻璃的无序结构，这两种结构都是工业中重要的材料类别。然而，星系团的准备和实验研究仍然很困难。这个项目将利用一种新的方法来制造集群，这种方法使用被称为胶体的微观颗粒，可以用光学显微镜看到。将使用一种先进的全息成像方法来观察星团中粒子的运动。该项目将培养一名物理学、材料科学和全息术的博士生和本科生，这是一个新兴的高科技领域。该项目还将通过一系列旨在激励他们继续学习科学的有趣、吸引人的实验室来教育20-40名公立高中生物理和光学。

****Technical Abstract****The structures and transitions of colloidal clusters may reveal local mechanisms governing bulk phenomena such as nucleation and structural arrest. Such clusters are also useful model systems for understanding self-assembly pathways. This experimental program will investigate three-dimensional colloidal clusters composed of 6-30 particles held together by weak interactions such as depletion or DNA-mediated binding. An advanced imaging method, digital holographic microscopy, will be used to measure the positions and motions of every particle in a cluster with sub-millisecond temporal resolution and 10 nm precision in all three dimensions. This technique enables detailed, quantitative studies of the ground states, equilibrium structural transitions, and topological transitions of the clusters. Results will be compared and used as input to energy landscape calculations, with the broad goal of understanding how phase transitions and nonequilibrium phenomena emerge as the size of the system increases. The program will train a graduate student and undergraduate in soft matter physics and applied optics. An outreach and education program will bring 20-40 high-school physics students from Cambridge and Boston-area public schools to Harvard for a series of discovery-based labs on waves, optics, and holography.****Non-Technical Abstract****This award supports experimental research on unusual materials called clusters, sometimes called an "intermediate state of matter." Compared to the usual states of matter we encounter in our daily lives -- gases, liquids, and solids -- clusters consist of a far smaller number of atoms or particles. Because they are less complex than ordinary matter, they are in principle easier to understand. Studying how these clusters change their shapes over time and in the presence of external forces could help solve longstanding challenges in materials science, such as how crystals form and why they sometimes form disordered structures called glasses, both of which are important classes of materials for industry. However, clusters remain difficult to prepare and study experimentally. This project will take advantage of a new way to make clusters using microscopic particles called colloids, which can be seen with an optical microscope. The motion of particles in the clusters will be observed using an advanced imaging method involving holograms. The project will train a Ph.D. student and undergraduate in physics, materials science, and holography, an emerging high-technology field. The project will also educate 20-40 public high school students in physics and optics through a series of labs designed to be fun, engaging, and aimed toward motivating them to continue studying science.