Probing 2-D Coalescence and Aggregation with Tunable Paramagnetic Colloidal Clusters

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CBET - 1705703PI: Biswal, Sibani L.Coalescence of liquid droplets and aggregation of colloidal particles are important in materials processing applications and in naturally-occurring processes. Coalescence and aggregation have been studied extensively for droplets and particles that are freely suspended in bulk liquids. This award will support research into aggregation of colloidal particles that are confined to a surface. The dynamics of aggregation in this case are expected to be fundamentally different than aggregation of particles in the bulk. The key challenge in studying aggregation is to control the forces between particles that can lead to aggregation. In this project, that challenge will be addressed by using clusters of superparamagnetic particles and placing the system in a rotating magnetic field. The aggregation of the colloidal clusters will be examined under conditions where the forces between the clusters can be tuned and are known at all times. The dynamics of cluster aggregation, changes in the arrangement of particles within the clusters, and the resulting structure that is obtained after aggregation will be studied. The results will be useful to material scientists and process engineers who are developing new two-dimensional materials that have unique electronic, optical, or catalytic properties. It will also provide new insight into other engineered materials that have interfaces or grain boundaries that can affect materials processing and reliability. The project will engage students at various academic levels, including community college students who participate in a summer program at Rice. Demonstrations of the unique properties of magnetic colloidal suspensions will be developed for local high-school students.This award will support an experimental study of coalescence and aggregation of two-dimensional colloidal clusters. The clusters will consist of micron-sized superparamagnetic colloidal particles dispersed in aqueous solution. A high frequency rotating magnetic field will be applied, resulting in a long-range, isotropic attractive interaction potential between the paramagnetic colloids that can be precisely tuned from 3kBT to 40kBT by varying the strength of the magnetic field. The experiments will determine how the interactional potential influences properties such as line tension and interfacial thickness. The experiment will be designed to monitor coalescence and aggregation as a function of interaction potential and to understand how void spaces are annealed during the assembly of clusters. Finally, the project will focus on the formation of disclinations and defects in two-dimensional systems and their implications on two-dimensional cluster dynamics.