Thermally Activated Dynamics in 2D Colloidal Glasses and Crystals

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Non-technical abstract: In this project, the team seeks to uncover the microscopic mechanism(s) by which many materials change suddenly from a liquid to a solid without the usual crystallization process. The most familiar one is the window glass. Whether the window glass is a slowly aging liquid or a true solid is a longstanding unresolved question in science. Building on the recent research in two-dimensional (2D) colloidal glasses, the team plans to use both experiment and theory to study the origin(s) of the glass transition. The experimental and theoretical activities will benefit each other, providing motivation and testing of the hypotheses. The results of this research can benefit scientists and engineers in designing new materials. For example, understanding the mechanism(s) of how impurities or particle size variations impact the stability of the glassy material may allow scientists to artificially engineer such impurities to improve the properties of the materials, similar to introducing impurities into superconductors to make stronger magnets. The proposed research provides excellent training for two Ph.D. students, and undergraduate and master students in condensed matter physics. Training the next generation American scientists in materials science is of great importance in maintaining the US preeminence in science and technology. Technical abstract:The team plans to use video microscopy and Monte Carlo simulations to study two sets of related questions in condensed matter physics: (1) What is the microscopic mechanism in the recently discovered 2D colloidal glasses of anisotropic particles? (2) Does an array of edge dislocations formed along a low-angle grain boundary in a 2D colloidal crystal undergo a finite temperature phase transition and what happens to the phase transition when there are impurity particles in the hosting 2D crystal? The underlying fundamental question is how phases of matter and phase transitions are impacted by disorder. The first project will investigate the physical mechanism of a two-step 2D colloidal glass transition of rods. The proposed experiments will be used to distinguish various competing scenarios of the glass transition in 2D. The second project is to study a possible novel phase transition in an array of edge dislocations formed along a low-angle grain boundary in a 2D colloidal crystal and the effects of disorder on the phase transition and dynamics. The results will have a significant impact on the understanding of defects and the glassy states in condensed matter systems. The results of this research can help scientists and engineers in designing new materials for the benefit of society.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.