Hindered Nanoparticle Diffusion and Void Accessibility in a Three-Dimensional Porous Medium

Abstract

The inherent pore-scale heterogeneity of many natural and synthetic porous materials can make it difficult to model and predict porous transport because the underlying microscopic processes are often poorly understood. Here we present the results of single-particle tracking experiments in which we followed the pore-scale diffusion of individual nanoparticles, deep within a three-dimensional porous material of moderate porosity. We observed significant hydrodynamic damping of particle motion at subpore length scales, resulting in heterogeneous and spatially dependent mobility. The accessibility of the void space was strongly dependent on particle size, and related to the heterogeneous hydrodynamics. Our results suggest that pore-scale diffusion is more heterogeneous and volume accessibility more limited than previously expected. The method demonstrated here will enable studies of a broad new class of materials including porous polymers of technological interest.

Diffusive dynamics of nanoparticles in ultra-confined media

“…14 Similar slowing of Fickian diffusion coincident with non-Gaussian distributions of particle displacements has been observed in a variety of systems, including hard sphere colloidal dispersions, 15,16 polymers in an array of pillars, 17 nanoparticles in a porous polymer matrix, 18 and colloids in a matrix of entangled F-actin polymers. Thus particle diffusion typically becomes slower in confinement.…”

Probing Non-Gaussianity in Confined Diffusion of Nanoparticles

“…Different from previous studies, 4,5,20 the standard Gaussian distribution with probability density function Figure 3b. Figure 3c further shows that the tail distribution becomes more pronounced with decreasing NP size.…”

Wettability alteration of oil-wet carbonate by silica nanofluid

“…We note that pressure and particularly temperature can significantly affect nanofluid properties [28], thus nanofluid behaviour and efficiency at reservoir conditions may be different; furthermore nanofluid efficiency is also likely affected by rock heterogeneity, which influences nanoparticle transport within the solid matrix [43].…”

“…All experiments were conducted at ambient conditions. At reservoir conditions, however, significantly higher pressures and elevated temperatures prevail, and as pressure and particularly temperature can affect nanofluid properties [28], nanofluid efficiency at reservoir conditions may be different to that measured at ambient conditions; furthermore, nanofluid efficiency is probably also influenced by rock heterogeneity, which determines nanofluid flow and distribution [5,43] throughout the formation.…”