Tagged-particle dynamics in confined colloidal liquids

Abstract

We present numerical results for the tagged-particle dynamics by solving the mode-coupling theory in confined geometry for colloidal liquids (cMCT). We show that neither the microscopic dynamics nor the type of intermediate scattering function qualitatively changes the asymptotic dynamics in vicinity of the glass transition. In particular, we find similar characteristics of confinement in the low-frequency susceptibility spectrum which we interpret as footprints of parallel relaxation. We derive predictions for the localization length and the scaling of the diffusion coefficient in the supercooled regime and discover a pronounced non-monotonic dependence on the confinement length. For dilute liquids in the hydrodynamic limit we calculate an analytical expression for the intermediate scattering functions, which is in perfect agreement with event-driven Brownian dynamics simulations. From this, we derive an expression for persistent anti-correlations in the velocity autocorrelation function (VACF) for confined motion. Using numerical results of the cMCT equations for the VACF we also identify a cross-over between different scalings corresponding to a transition from unconfined to confined behaviour.

Structural properties of liquids in extreme confinement

“…4 with L = 0.5σ which corresponds to n 0 L 2 = 0.143. This analysis therefore shows again that the effects of confinement are strongly enhanced for denser packings [49].…”

Layering and packing in confined colloidal suspensions

“…Confinement changes, for example, the structure and phase behaviour, [1][2][3][4][5][6][7][8][9][10][11][12] dynamics and viscoelasticity, [12][13][14][15][16] and glass transition. [17][18][19][20][21][22][23][24] It affects atomic, molecular, as well as colloidal fluids. Correspondingly, confinement is relevant for many areas, ranging from physics, chemistry, biology, and medicine to environmental and material sciences as well as technology.…”

Tagged-particle motion in quasi-confined colloidal hard-sphere liquids

“…The MCT equations of the quasi-confined liquid are reminiscent of the diagonal approximation for the slit geometry. Therefore, a detailed MCT analysis [64,77,78] can easily be adopted to quasi-confined liquids. Yet, we want to emphasize that for quasi-confined liquids it is an exact representation rather than an approximation.…”

“…. At intermediate times we then expect to observe two additional power laws, which are directly related to the critical beta decay [64].…”

“…For large confinement lengths (L 5.0σ) the dynamics of the particle are indistinguishable from bulk motion for short times with an intermediate window, where the VACF decays with a power-law, Z(t) ∼ −t −5/2 . Only for longer times, a crossover from the unconfined dynamics occurs and the expected power law for quasi-confinement, Z(t) ∼ −t −2 , is observed, similar to the tagged-particle within a slit [64]. Extreme confinement, however, cannot be considered as the two dimensional limit case since due to periodic boundary conditions the hard spheres are still able to move perpendicular to the confining direction.…”