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

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

Non-technical Abstract The 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 Abstract This 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.