Complex dynamics induced by strong confinement – From tracer diffusion in strongly heterogeneous media to glassy relaxation of dense fluids in narrow slits

Abstract

Abstract. We provide an overview of recent advances of the complex dynamics of particles in strong confinements. The first paradigm is the Lorentz model where tracers explore a quenched disordered host structure. Such systems naturally occur as limiting cases of binary glassforming systems if the dynamics of one component is much faster than the other. For a certain critical density of the host structure the tracers undergo a localization transition which constitutes a critical phenomenon. A series of predictions in the vicinity of the transition have been elaborated and tested versus computer simulations. Analytical progress is achieved for small obstacle densities. The second paradigm is a dense strongly interacting liquid confined to a narrow slab. Then the glass transition depends nonmonotonically on the separation of the plates due to an interplay of local packing and layering. Very small slab widths allow to address certain features of the statics and dynamics analytically.

Molecular dynamics simulations of propane in slit shaped silica nano-pores: direct comparison with quasielastic neutron scattering experiments

“…Molecular motion under confinement is an interesting topic of research as it entails a variety of peculiar phenomena [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] . Anomalous size and loading dependence of molecular dynamics of confined fluids in porous media have been reported [6][7][8] , suggesting the need of better understanding how confinement affects not only the structure but also the transport-properties of confined fluids.…”

Random motion of a circle microswimmer in a random environment

“…To extend our understanding of transport properties of real systems, both these constraints should be relaxed. The paradigmatic Lorentz model [38,39,40] constitutes a reference system to study how transport properties of probe particles in heterogeneous media depend on the microscopic motion of the particles and their environment [41,42,43,44]. The main feature of the Lorentz model is that the obstacles are placed randomly and can overlap.…”

Recent advances on glass-forming systems driven far from equilibrium

“…The dependence of the breakdown of linear response to the chosen external field variable for the different experimental protocols needs careful consideration from the theoretical perspective as described in reference [3]. Furthermore, in reference [8] the breakdown of linear response when approaching the critical point in Lorentz gases is monitored, revealing where the impact of increasing correlation lengths can be studied. In the framework of the potential energy landscape analysis, the breakdown of linear response in sheared supercooled liquids is related to a reduction of energy barriers or to an increase of the effective temperature [4].…”

“…Dynamical heterogeneities exhibit length scales which can only be resolved when considering time-dependent correlation functions. Micro-rheology has turned out sensitive to these heterogeneities [4,8] considering single probes driven through well-characterized models of heterogeneous media or simple particle models. Changing the character of the disorder in the surrounding matrix, and the interactions between mobile particles when their concentration increases, and between particle species of strongly different mobility, the relevant time-dependent correlation functions and susceptibilities are determined in simulations and analytical models.…”

“…They find sub-diffusive as well as super-diffusive behavior for intermediate times depending on the interactions and explain how simple models can be mapped onto more complex situations like motion in glass formers. Recent progress in analytical approaches to determine asymptotic laws for anomalous motion or non-analytic field dependences is summarized in the review by Mandal et al [8]. The analysis of some of the models simulated can be performed rigorously, e.g., for low densities or close to a percolation transition.…”