SKM 2023 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 50: Glasses and Glas Transition II

CPP 50.2: Talk

Thursday, March 30, 2023, 12:30–12:45, ZEU 255

Roughness Induced Rotational Slowdown near the Colloidal Glass Transition — Beybin Ilhan, Michel Duits, and •Frieder Mugele — University of Twente, Physics of Complex Fluids group

Rotational diffusion of colloidal spheres has been studied rarely, in spite of its importance in the kinetics of many processes involving friction. While for smooth hard spheres, rotational diffusion gets impeded only weakly with increasing volume fraction, the picture changes drastically when surface roughness is introduced. We show this for a system of undeformable all-silica colloidal raspberries, studied with time-resolved 3D Confocal Scanning Laser Microscopy (CSLM).

We find that the strong surface roughness leads to a significantly lower maximum volume fraction, preceded by a broad concentration range in which the rotational Brownian motion changes signature from high-amplitude diffusive to low-amplitude rattling. This strong rotational slowdown occurs at significantly higher concentrations than for the translations, thus presenting a second glass transition.

In the regime where the Mean Squared Angular Displacement (MSAD) is subdiffusive, significant correlations are found between the translational and rotational motions. The drastic rotational slowdown occurs when the particle intersurface distance becomes comparable to the surface roughness amplitude. Concurrently, the number of contacts exceeds a critical value. This picture is supported by observations in a densely packed layer of raspberries at a smooth wall: here significant rotational motions are found while the translations are almost completely frozen.