Laboratoire Matière et Systèmes Complexes

Pre-adsorption dynamics of patchy colloids on flat substrate : Brownian Rock & Roll

Dražen Zanchi Ecole Normale Supérieure (Département de Chimie, UMR 8640 PASTEUR) and Université Paris Diderot, (UFR de Physique).

Abstract : Immediately before adsorption to a horizontal substrate, sinking soft colloids can undergo a complex sequence of landing, jumping, crawling and rolling events. Using video tracking we studied the soft adhesion of micron-size colloids coated by polymer PNIPAM which is temperature sensitive. It allows for sticking of colloids to the surface when the temperature is above Tc = 32°C. In order to capture the very final events before the immobilization of colloids the T-ramp protocol was designed : the particles suspension is injected in the cell at room temperature, the temperature is increased at 10°C/min up to 38°C (>Tc), and kept constant until the end of the acquisition. Attraction between beads and the flat plate is thereby triggered by crossing the critical temperature Tc = 32°C. 3D beads motion is observed by slightly defocus microscopy in parallel illumination decorating bead image with interference rings observed with video camera, and tracked in real time. Analysis of the tracking records indicates the Brownian rolling is the most relevant phenomenon before the immobilization. There are fundamental differences between Brownian rolling and Brownian jumping. In particular, we point out on the possibility of exploiting rolling of colloids over the substrate as a novel strategy of separation. The colloids with same coverage (sticky surface fraction) but with different disposition of sticking patches can be resolved.

Reference : Giuseppe Boniello, Christophe Tribet, Emmanuelle Marie, Vincent Croquette, and Dražen Zanchi, Rolling and aging in temperature-ramp soft adhesion, Physical Review E 97(1):012609 (2018).