Résumé
Dynamics of anisotropic particles at a fluid interface governs trapping and particles subsequentassembly. Measuring and controlling this viscous dynamics open the way to new materials [1], andapplications [2]. Despite these domains of applications, measurements of the viscous coefficient ofanisotropic particles were mainly restricted to the bulk [3-4] or in quasi-2D confinement between twoglass plates [5]. Here we measure the complete set of viscous coefficients of single micrometricprolate ellipsoids near and trapped at an air-water interface. These coefficients are obtained from theBrownian motion of the particle coupling interferometry and particle tracking. For particles trapped atthe interface we measured anomalously large drags even larger than in the bulk water (ratio of surface/bulk rotational drags rR > 1 in Figure) [6]. Such an intriguing behaviour is discussed in terms ofadditional random forces due to thermally activated fluctuations of the interface and their coupling tothe particle drag through the fluctuation–dissipation theorem.Figure: Rotational viscous-drag ratio rR (surface/bulk) of polystyrene ellipsoidal particles at anair/water interface versus particle’s aspect ratio φ. Inset: mean square angular displacements (MSADs)versus the time lag τ.[1] M. Cavallaro, L. Botto, E. Lewandowski, M. Wang, and K. Stebe, PNAS 108, 20923 (2011).[2] Z. Huang, D. Legendre, and P. Guiraud, Chem. Eng. Sci. 66, 982 (2011).[3] D. Mukhija and M. Solomon, J. Colloid Interface Sci. 314, 98 (2007).[4] T. H. Besseling, M. Hermes, A. Kuijk et al., Journal of Physics: Condensed Matter 27, 194109 (2015).[5] Y. Han, A. Alsayed, M. Nobili, J. Zhang, T. Lubensky, and A. Yodh, Science 314, 626 (2006).[6] G. Boniello, C. Blanc, D. Fedorenko, M. Medfai, N. Ben Mbarek, M. In, M. Gross, A. Stocco, M. Nobili,Nature Materials 14, 908 (2015).