(219b) Non-Equilibrium Dynamics of Nanoparticle-Laden Fluid Interfaces

Processes in which an interface is formed in a complex fluid containing dispersed particles are ubiquitous in industrial and technological applications (e. g. coating flows of particle-laden fluids, material deposition by ink-jet printing methods, and formation of droplets or bubbles in microfluidic devices). This research lays the basis for understanding the dynamics of nanoparticle-laden interfaces far from equilibrium. We investigate the mechanism of aggregation of nanoparticles adsorbing at a water-oil interface from an aqueous solution. We use pendant drop tensiometry to characterize the kinetics of nanoparticle adsorption as a function of bulk concentration, particle size and shape. Thermodynamic and mass transfer arguments typically used to model surfactant adsorption are extended to particle monolayers, with the notable difference that, unlike soluble surfactants, particles bigger than a few nanometers adsorb at the interface irreversibly, i.e. the energy of detachment is inaccessible to thermal excitation. To monitor the interfacial structure in situ , we use passive microrheology through multi-particle tracking of sparse probe microspheres co-adsorbed at the interface.