Colloids as Models for Crystals and Glasses

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Non-technical AbstractColloids are collections of small particles suspended in a liquid. They occur in many different places in everyday life, such as paints and milk. The properties of these colloids can be controlled by varying the size and composition of the particles allowing them to serve as models for atomic systems. This project will explore the properties of colloids to obtain a better understanding of the various phases (liquids, crystals, glasses) of atomic and molecular systems. Colloids offer an advantage in this study since the location of individual particles can be tracked in 3D. In addition, the PI's will develop new techniques that will allow more control of the particles in the colloids. The project will provide training for graduate and undergraduate students in state-of-the-art synthesis and measurement techniques. In addition, the relative simplicity and the visual character of the experiments make them highly accessible to the public.Technical AbstractThis project will use colloidal particles as models for the study of interesting and important phase behavior of a variety of solid phases. Colloids offer the unique advantage in that the motion of individual particles can be tracked. This enables direct three-dimensional, time-dependent imaging of complex dynamic processes, such as crystallization, nucleation or deformation, on the molecular level; these processes are common to both colloidal systems as well as molecular systems. This capability will be exploited in the work proposed to investigate new properties of the phase behavior of solids, including phase transitions between amorphous and crystalline states, solid-solid phase transitions and the nature and dynamics of the amorphous state and the interfaces of crystalline materials. An important part of the project is the development of new experimental tools. One of them is the "electric bottle", in which the particle density is controlled by dielectrophoresis. New types of electrodes are being developed to aid in the study of phase transformations, in particular homogeneous crystal nucleation from the melt and solid-solid transformations. A second tool being developed is a highly sensitive traction-force method for measuring the stress in a colloidal crystal or glass during deformation. The tool will also present the rheology community with a new, highly sensitive instrument. The colloids also provide a unique opportunity to study the mobility and fluctuation dynamics of a large variety of random and engineered three-dimensional grain boundaries.