Nanoparticle Tracking to Probe Transport in Porous Media

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: From the granular and fractured subsurface environment to highly engineered polymer membranes used in pharmaceutical purification, porous materials are ubiquitous in nature and industrial applications. In particular, porous media are used extensively in processes including water treatment, pharmaceutical sterilization, food/beverage processing, and heterogeneous catalysis, where hindered mass transport is either essential to the process or a necessary but undesirable limitation. Unfortunately, there are currently no universal models capable of predicting mass transport based on a description of the porous material because real porous materials are complex and because many coupled dynamic mechanisms (e.g., adsorption, steric effects, hydrodynamic effects, electrostatic interactions, etc.) give rise to the observed macroscopic transport phenomena. While classical techniques, like nuclear magnetic resonance and dynamic light scattering, 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.In this Account, we summarize our recent efforts to advance the understanding of nanoparticle transport in porous media using single-particle tracking methods in both fundamental and applied scenarios. First, we describe the basic principles for twodimensional and three-dimensional single-particle tracking in porous materials. Then, we provide concrete examples of nanoparticle transport in porous materials 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, and (2) facilitating applications in industrial processes, e.g., by understanding the mechanisms of particle fouling and remobilization in filtration membranes. Finally, we provide an outlook of opportunities associated with investigating other types of mass transport in confined environments using single-particle tracking methods, including electrophoretic and self-propelled motion.

Fluorescence Microscopic Investigations of Molecular Dynamics in Self‐Assembled Nanostructures

“…Indeed, SMT and related techniques have unveiled molecular dynamics at solid‐liquid interfaces [67–70] relevant to chromatography, membrane separations, and electrochemical sensing. In particular, 3D single particle/molecule tracking methods, rather than 2D counterparts introduced in this account, are promising for in situ visualization of molecular separation mechanisms in real membranes [71,72] . Molecular‐level details obtained from these studies will lead to in‐depth understanding of the impacts of material heterogeneity on molecular separation mechanisms, and thus will help develop highly efficient separation and sensing media.…”

Viral Filtration: A Review of Current and Future Practices in Bioprocessing

“…The advent of single-particle tracking technologies such as the nanoparticles presented by Wu et al 2020 have been used in PVDF membrane filters. n these technologies, nanoparticles are continuously imaged, such as with an optical microscope, and tracking algorithms implemented to localize particle positions and generate trajectories (Wu and Schwartz 2020) which theoretically could be adapted to viral filtration flow studies.…”

Stochastic Adsorption of Diluted Solute Molecules at Interfaces

“…Because our current measuring techniques, especially various chemical imaging methods, have discrete integration times, 4,6,[22][23][24]9,[15][16][17][18][19][20][21] finding the correlation between the continuous and discrete solutions of adsorption is important. The difficulty of understanding lies in the self-similar fractal nature of diffusion and its probability density function.…”

“…The non-Gaussian diffusion is often observed in a confined space or near a surface further complicated the problem. 7,16 The adsorption of the molecules is greatly affected by the reabsorption of the reflected molecules. 8 It is becoming important for us to re-evaluate the theory of adsorption under ideal conditions to reduce the difficulty in building or understanding more complicated models.…”