When a concentrated suspension of colloidal particles forms networks of particles, the result is a material called a soft colloidal gel. The elastic properties of colloidal gels can be tuned by changing the characteristics of the particles, which makes colloidal gels useful in many consumer products, agricultural applications, and pharmaceuticals. This award will support the development and characterization of colloidal gels that incorporate active particles into their structures. Active particles can generate their own propulsion under certain conditions. When active particles are embedded in a colloidal gel, the extent to which the properties of the gel can be varied and controlled is expanded, which could increase the use of colloidal gels in practice. The properties of the gels containing active particles will be investigated using a combination of microscopy and mechanical testing. Results of the research will be disseminated through an industry/academic workshop. In addition, the research will be used to create hands-on demonstrations for middle school girls participating in a summer school that introduces young students to engineering.
This project will establish the relationship between the microdynamics of active colloids embedded in colloidal gels and their macroscopic functional properties of linear elasticity and non-linear yielding. These micro/macro relationships will be generated by investigating active colloids introduced into fractal cluster gels, a system whose structure, dynamics, elasticity, and yielding are well understood for the case of passive, Brownian colloids. Active platinum Janus particles driven by hydrogen peroxide decomposition, two-channel confocal microscopy, fractal cluster gel self-assembly, and macroscopic rheology with a novel, permeable fixture will be used to discover: (i) how microscopic activity affects the linear elastic modulus of gels; (ii) how internally-induced yielding presents macroscopically, and; (iii) how consolidation and disintegration of gels is produced by the external pressure of active colloids. The work will yield insight into how the unusual microdynamics of active systems determine their macroscopic rheological function.
