(3fh) Nanoparticle Tracking to Probe Transport in Porous Media

Porous materials are used extensively in processes including pharmaceutical sterilization, water treatment, food/beverage processing and heterogeneous catalysis. Moreover, many geological and biological environments are porous. Unfortunately, there are currently no universal models able to predict mass transport based on a description of the porous material as real porous materials are complex, and many coupled dynamic mechanisms (e.g., hydrodynamic effects, steric effects, electrostatic interactions) give rise to the observed macroscopic transport phenomena. While classical techniques, like dynamic light scattering and nuclear magnetic resonance, provide useful information about mass transport in porous media at the ensemble level, they provide limited insight into the microscopic mechanisms that give rise to complex phenomena such as anomalous diffusion, hindered pore-space accessibility, and unexpected retention under flow, among many others. To address this issue, we have developed refractive index matching imaging systems, combined with single-particle tracking methods, allowing the direct visualization of single particle motion within a variety of porous materials. Here, concrete examples of investigating nanoparticle transport in porous materials by particle tracking will be illustrated from two perspectives: (1) understanding fundamental elementary particle transport processes in porous media, including pore accessibility and cavity escape, which limit transport in porous media; (2) facilitating applications in industrial processes, e.g. by understanding the mechanisms of particle remobilization in filtration membranes.