ISS: Collaborative Research: Bimodal Colloidal Assembly, Coarsening and Failure: Decoupling Sedimentation and Particle Size Effects

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A wide range of natural and artificial materials are composed of different components - such as particles and polymer molecules - dispersed in a fluid. Examples are personal care products, food, and inks. Physical properties and function of these products, along with their shelf-life and consumer perception, depend on the behavior of these components. Designing materials with specific desired properties, therefore, requires a better understanding of how these particles and polymers interact under different conditions. Of particular interest are gel-like systems where particle size variations can lead to product failure. This award will combine computer simulations and terrestrial experiments, along with experiments onboard the International Space Station. The goal is to examine the effect of gravity on these gels and to investigate the size variation effects on final properties of such materials. Such findings could benefit several industries and will also help opening new avenues of fundamental research. A series of outreach activities are proposed to enhance the participation of traditionally underrepresented groups in STEM fields.In this project, we will study the physics of colloidal gelation, coarsening and phase-separation in bimodal attractive colloidal suspensions, in which the size difference between the two particle populations is appreciable. This size disparity can cause selective gravitational settling in one hand, and heterogeneous clustering where large particles serve as nuclei for aggregation of small colloids in another hand, leading to coarsening and failure of the gels. The role of particle size difference in coarsening and eventual failure of colloidal gels will be probed by decoupling the role of gravitational forces and inter-particle interactions. The ultimate goal is to explore the role of particle composition (ratio of small to large particles) as well as the range of interactions between the particles in mediating gelation, coarsening, and [gravitational] failure. An integrated effort, with detailed study of the physical phenomena through computational/theoretical platforms in conjunction with control ground experiments in addition to essential micro-gravity experiments will be performed. The cohesive integration of theory, computation and experiments with and without gravity will enable us to systematically decouple the roles of gravity and particle size disparity in mediating gelation, coarsening, and failure, paving the way for the development of a theoretical framework to better understand attractive colloidal systems in real-world applications.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.