Tagged-particle motion in a dense confined liquid

Abstract

We investigate the dynamics of a tagged particle embedded in a strongly interacting confined liquid enclosed between two opposing flat walls. Using the Zwanzig-Mori projection operator formalism we obtain an equation of motion for the incoherent scattering function suitably generalized to account for the lack of translational symmetry. We close the equations of motion by a self-consistent modecoupling ansatz. The interaction of the tracer with the surrounding liquid is encoded in generalized direct correlation functions. We extract the in-plane dynamics and provide a microscopic expression for the diffusion coefficient parallel to the walls. The solute particle may differ in size or interaction from the surrounding host-liquid constituents offering the possibility of a systematic analysis of dynamic effects on the tagged-particle motion in confinement.

Nonlinear response and emerging nonequilibrium microstructures for biased diffusion in confined crowded environments

“…Indeed, the study of driven diffusion in confined geometries [11], e.g., in micro-channels, where the surface-to-volume ratios are large, opened up a broad front of research, with important applications in several fields, such as, e.g., microand nanofluidics [12,13], hydrodynamics at solid-liquid interfaces [14], reaction-diffusion kinetics [15], dynamics of colloids [16][17][18][19] and polymers [20], dense liquids [21], and crowded systems [22,23].…”

Communication: Local structure-mobility relationships of confined fluids reverse upon supercooling

“…Despite providing other important insights, previous investigations directly measuring inhomogeneous dynamics have studied a variety of fluids governed by disparate interactions, external fields, and conditions, and they have also used different protocols to characterize the dynamics. 9,11,13,14,[38][39][40] As a result, even fundamental questions related to confined (and more generally inhomogeneous) fluids remain open: Do local and average correlations between particle mobility and structure universally reflect bulk behaviors? Do new structuremobility relations emerge as inhomogeneous fluids are supercooled toward glass transitions?…”

“…As a result, the static properties of confined fluids, such as local one-body density ρ(z), are now well-understood in terms of physical intuition (e.g., emergence of particle layering near boundaries to relieve packing frustration 1,2 ) and can be predicted using microscopic approaches like density functional theory. 3,4 However, much less is understood about what controls the dynamics of inhomogeneous fluids, and only recently have efforts broadened to include developing theories [5][6][7][8][9][10][11] and other tools [12][13][14][15][16] for characterizing particle dynamics both on a spatially averaged basis and as a function of position.…”

Enhanced diffusion in finite-size simulations of a fragile diatomic glass former

“…Previous experiments and simulations using confinement found, depending on the conditions, mostly an increase, but sometimes a decrease of the viscosity with the system size [45][46][47][48][49][50][51][52][53][54][55][56] . However previous finite systems simulations [22][23][24][25][26][27][28][29][30][31][32] found to our knowledge always an increase of the viscosity together with a decrease of the cooperativity when the system size decreases.…”

“…In this work we study finite size effects using molecular dynamics simulations of a simple molecular liquid. We use finite size simulations [22][23][24][25][26][27][28][29][30][31][32] instead of confinement [45][46][47][48][49][50][51][52][53][54][55][56] because finite size simulations have the advantage over confinement to cut off the cooperativity without introducing any confining wall nor modifying the symmetry or the dimensionality of the system, as long as periodic boundary conditions are used. The simplicity of the molecule permits us to access large time scales with aging times larger than the micro-second.…”