CAREER: Using Three-Dimensional Confocal Rheology to Measure Shear Induced Microstructural Deformations in Colloidal Glasses

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Non-Technical AbstractComplex fluids are fascinating materials with unique properties that arise from familiar constituents. For example, emulsions and foams such as salad dressing and seat cushions are comprised of simple materials such as liquid and air, yet their material properties remain topics of overwhelming interest. The goal of this Early Faculty CAREER Award is to gain a broader understanding of the glass transition by using emulsions -- a particularly interesting complex fluid. Emulsions are collections of very small liquid droplets, dispersed within another fluid, that closely mimic the behavior of atoms and molecules. However, due to their relatively large size, direct and real-time measurements of their positions and motions are obtainable in contrast to their atomic counterparts. The glass transition describes a transition in liquids that leads to their solidification when they are abruptly cooled. Rapid cooling forces the material to remain disordered while somehow becoming a solid. Remarkably, when these fluid droplets are tightly packed together, they undergo a transition where all of the droplets jam up, resulting in a material that is structurally very similar to window glass. By simultaneously deforming and imaging a glass comprised of emulsion droplets information about the mechanical properties, including the force on each droplet, can be directly measured. This information will provide key insights into the origins of the glass transition and will aid in the development of theoretical models that describe these complex materials. A major educational component initiated by the PI is the development of the Mid Atlantic Soft Matter Workshop (MASM). This workshop provides an ideal forum for researchers within the region whose interests reside at the interface of conventional disciplines. The workshop also naturally assists in the career advancement of young scientists by acquainting them with the local academic and industrial research community. Technical AbstractThe research in this Early Faculty CAREER Award is focused on developing the unique ability to precisely control and determine the mechanical properties within soft glassy solids at the bulk and microscopic scales. A system of colloidal suspensions (emulsions) is utilized to create materials that undergo kinetic arrest similar to the glass transition in a variety of condensed materials. What makes the experimental program described in this proposal unique is the development of methods to impose precise shear stresses during direct high speed three dimensional imaging. This technology will allow the system to be externally driven and measured (rheology) while simultaneously measuring the dynamic and structural evolution of the material at the microscale. To carry out this proposed research, two well established techniques for quantifying soft materials are combined; confocal microscopy and bulk rheology. From a broader perspective, measurements of the microstructure within colloidal glasses will allow for the development of microscopic theories of amorphous materials that will provide both practical and fundamental insights. A major outreach component initiated by the PI is the development of the Mid Atlantic Soft Matter Workshop (MASM). This workshop provides an ideal forum for researchers within the region whose interests reside at the interface of conventional disciplines. The workshop also naturally assists in the career advancement of young scientists by acquainting them with the local academic and industrial research community.