Can local salt gradients at microscale impact the macroscopic transport of colloids in a porous medium?*

Flows containing dissolved salts and suspended particles in a porous medium can occur in a variety of natural and engineered scenarios where local salt gradients can induce particle motion via a phenomenon known as diffusiophoresis [1,2]. Although this contributes to the complexity of the overall transport problem, it can be exploited for a variety of technological applications [3-6]. Aiming to unravel the coupling of the underlying physical mechanisms, we conduct pore-scale simulations to investigate the fluid, solute and particle transport in a micromodel. We measure the time-lapsed effluent concentration of the colloidal particles close to the outlet and compute the so-called breakthrough curves to understand the influence of diffusiophoresis on the particle macroscopic transport through the whole host medium. Our results hint towards the fact that the microscopic interplay between diffusiophoretic particle motion and host medium disorder can impact the macroscale particle dynamics. Lastly, while both, the flow and transport through a porous medium and the diffusiophoretic motion of colloids in a variety of microfluidic devices, are active areas of research, the novelty of our work lies in the intersection of the two.

References:

[1] Derjaguin et al. (1947), “Kinetic phenomenon in boundary films of liquids”, Colloid J. USSR, 9, 335-347.

[2] Anderson (1989), “Colloid transport by interfacial forces”, Annu. Rev. Fluid Mech., 21 (1), 61-99.

[3] Kar et al. (2015), “Enhanced Transport into and out of dead-end pores”, ACS Nano, 9(1), 746-753.

[4] Shin et al. (2017), “Membraneless water filtration using CO2”, Nat. Commun., 8(1), 15181.

[5] Rasmussen et al. (2020), “Size and surface charge characterization of nanoparticles with a salt gradient”, Nat. Commun., 11(1), 2337.

[6] Jotkar & Cueto-Felgueroso (2021), “Particle Separation through Diverging Nanochannels via Diffusiophoresis and Diffusioosmosis”, Phys. Rev. Applied., 16, 064067.