Roughness induced rotational slowdown near the colloidal glass transition

Activity: Talk or presentationOral presentation

Description

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) [1,2].
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.
Keywords: surface roughness, rotational diffusion, glass transition, confocal microscopy

References
[1] B. Ilhan, J.J. Schoppink, F. Mugele, M.H.G. Duits, Journal of colloid and interface science, 2020, 576, 322-329.
[2] B. Ilhan, F. Mugele, M.H.G. Duits, Journal of colloid and interface science 2022, 607, 1709-1716.
Period4 Sept 2023
Event title37th European Coloid & Interface Society (ECIS) Conference 2023
Event typeConference
Conference number37
LocationNapels, ItalyShow on map
Degree of RecognitionInternational