(399a) Electrokinetic Transport Dynamics of Nanoparticles in 3D Ordered Porous Media

Energy-related separation technologies typically involve mass transport in complex, heterogeneous, interface- and species-rich environments. Electric field is a popular and versatile tool to manipulate the transport components due to its ease of operation and integration into systems at multiple scales, ranging from bio-inspired nanopore systems to microfluidic devices and industrial operational setups. This study focused on the electrokinetic transport dynamics of carboxylic-acid functionalized polystyrene nanoparticles within a ordered porous media (inverse opals) under a direct-current (DC) electric field. Captured by 3D single-nanoparticle fluorescence imaging, an enhancement in nanoparticle diffusion and transport efficiency in the porous media was observed under the DC field compared to passive Brownian particles. Notably, within the porous media, a critical electric field strength required to initiate advective motion of nanoparticles was identified; the dependency of this field-strength threshold on pore (exit) size, ionic strength, and surface charges indicates the intricate interplay between confinement effects and electric double layer interactions at the substrate-nanoparticle interface. Moreover, we established a relation between the macroscopic advection of the nanoparticle (represented by the Péclet number) and the ratio of its transport bias to residence time at the single-cavity level; the decoupling of the microscopic residence time and transport bias from macroscopic parameters offers new insights into electrokinetic transport in complex environments. Overall, this finding advances our understanding in the field-driven nanoparticle transport within 3D interface-rich environments, serving as a good foundation for optimizing electrokinetic systems for applications in separation, mixing and analyte detection.