CAREER: Novel Self-Assembly and Phase Transitions in Single- and Multi-Component Colloidal Crystals

摘要单组分和多组分体系所表现出的各种结构组织和相变，如熔融、冻结、玻璃化和固-固相变，在自然界中随处可见。然而，缺乏对三维晶体内部局部微观动力学的测量，阻碍了对这些现象的理解。卡内基梅隆大学的教师早期职业发展（Career）项目的目标是使用温度响应微凝胶胶体球和视频光学显微镜来实验研究大块晶体的结构和动力学。由于原子或分子晶体的大小，在3D晶体中很难跟踪原子或分子，因此不可能使用原子或分子晶体。虽然在3D中更容易跟踪胶体颗粒，但很难在单个样品中连续改变控制相变的体积分数。在这个项目中，可以通过调节温度和修改系统的体积分数来精确调节胶体颗粒的大小。本项目中出现的自组装、扩散以及结构与动力学之间的关系等概念将被纳入现有的软材料课程中。此外，软材料的高度视觉性和互动性将通过使复杂的思想更加有形，吸引和激发本科生和高中生对高水平科学的兴趣。卡内基梅隆大学的教师早期职业发展（Career）项目将实验研究相同或不同大小的胶体硬球的三维（3D）晶体内部的结构和局部微观动力学，以阐明自组装和相变。不幸的是，由于难以跟踪原子或分子，在三维原子或分子晶体中研究这种现象是不可能的。虽然在3D中更容易跟踪胶体颗粒，但很难在单个样品中连续改变控制相变的体积分数。本项目的中心思想是采用热响应微凝胶胶体球和实时视频光学显微镜来实验研究原位胶体系统的相行为。微凝胶球的直径和体积分数可以通过调节温度来精确调节。该项目的研究结果将对扩散、自组装和粗化以及光子学、光刻、药物输送等功能材料的设计具有重要意义。此外，软材料的高度视觉性和互动性将使复杂的想法在许多层面上更加有形和智能地可访问，从而允许K-12适当的模块以及具有挑战性的本科和研究生课程。

Non-technical AbstractThe diverse organization of structures and varieties of phase transitions such as melting, freezing, glass transitions and solid-solid phase transitions exhibited by single- and multi-component systems are found throughout nature. However, measurements of local microscopic dynamics within the bulk of three dimensional (3D) crystals are lacking, hindering the understanding of these phenomena. The goal of this Faculty Early Career Development (CAREER) project at Carnegie Mellon University is to use temperature responsive microgel colloidal spheres and video light microscopy to experimentally investigate the structure and dynamics within the bulk crystals. It is impossible to use atomic or molecular crystals due to difficulty in tracking atoms or molecules in 3D crystals due to their size. While it is easier to track colloidal particles in 3D, it is difficult to continuously change the volume fraction, which controls phase transition, in a single sample. In this project, the size of the colloidal particles can be accurately adjusted by tuning the temperature and modify the volume fraction of the system. The emerging concepts in self-assembly, diffusion, and the relationship between structure and dynamics from this project will be incorporated in an existing course on soft materials. Furthermore, the highly visual and interactive nature of soft materials will attract and inspire undergraduates and high-school students to high-level science by making complex ideas more tangible.Technical AbstractThis Faculty Early Career Development (CAREER) project at Carnegie Mellon University will experimentally investigate the structure and local microscopic dynamics within the bulk of three dimensional (3D) crystals of colloidal hard spheres of identical or different sizes to elucidate self-assembly and phase transitions. Unfortunately, studying such phenomena within the bulk of a 3D atomic or molecular crystal is impossible due to difficulty in tracking atoms or molecules. While it is easier to track colloidal particles in 3D, it is difficult to continuously change the volume fraction, which controls phase transition, in a single sample. The central idea of this project is to employ thermally responsive microgel colloidal spheres and realtime video light microscopy to experimentally investigate the phase behavior of colloidal systems in situ. The diameter, and therefore the volume fraction, of the microgel spheres can be precisely adjusted by tuning the temperature. The results from this project will have important implications in diffusion, self-assembly and coarsening as well as in designing functional materials for photonics, lithography, drug delivery, etc. Furthermore, the highly visual and interactive nature of soft materials will make complex ideas more tangible and intellectually accessible on many levels allowing for K-12 appropriate modules as well as challenging undergraduate and graduate courses.