Probing Rotational Dynamics of Nanoparticle Dispersions via Dielectric Spectroscopy

The equilibrium properties of colloidal dispersions continue to attract attention due to the rich phase behavior observed in particle systems with a balance of attractive and repulsive interactions. Theoretical and experimental advances have used the tools of liquid state theory to revolution our understanding of pair-interactions, their mapping to a preferred microstructural configuration and the prediction of equilibrium thermodynamic properties. This approach, however, fails to quantitatively describe the macroscopic properties of dispersions in non-equilibrium states such as gels or glasses. Such states are frequently encountered in the processing of colloidal dispersions and in these applications their viscoelastic properties are relevant. It is thought that the presence and magnitude of local rigidity at the particle length scale can be a key distinguishing feature of the way particles restructure in response to stress and flow. This proposal explores new experimental approaches to probe both the local motion of colloidal particles within the gel state and the role played by rotational dynamics in determining the quiescent properties of gels. This study will leverage in situ characterization tools recently developed by the principal investigator that allow for the simultaneous interrogation of the dynamics and structure of non-equilibrium states in particle dispersions with various process histories. Our approach will provide an experimental foundation for understanding these local effects in colloidal gels and pave the way to designing new materials with adaptive microstructures and tunable viscoelasticity.