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You are here: Home / Seminars / Experimental physics and modelling / Equilibrium and non-equilibrium fluctuations in soft matter

Equilibrium and non-equilibrium fluctuations in soft matter

Roberto Cerbino (Université de Milan)
When Jun 05, 2018
from 10:45 to 12:00
Where Amphi Schrödinger
Attendees Roberto Cerbino
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In molecular mixtures kept outside of equilibrium by a macroscopic temperature or concentration gradient, the coupling between the gradient and velocity fluctuations produces spectacularly large and long ranged (giant) fluctuations, whose size and relaxation time are controlled on Earth by the presence of gravity [1]. So far, the experimental investigation of these phenomena in soft matter has been very limited. In this talk, I first describe recent experimental results obtained with dilute polymer solutions in microgravity [2,3]. In the second part of the talk, I present some results obtained on Earth with dense colloidal suspensions [4]. Using colloids in combination with Differential Dynamic Microscopy (DDM) [5] offered the unique opportunity of investigating the interplay between equilibrium and non-equilibrium fluctuations in controlled experiments, as well as characterising the fluctuations in the presence of very large gradients, a regime that challenges current linear theories. Our experiments suggest that using colloidal suspensions instead of molecular mixtures may offer several advantages, especially in connection with recent theoretical work that predicts the existence of large, experimentally unobserved Casimir forces during diffusion processes [6].
[1] Ortiz de Zárate, J.M. and Sengers, J.V.: Hydrodynamic fluctuations in fluids and fluid mixtures (Elsevier, Amsterdam, 2006).
[2] Vailati, A., Cerbino, R., Mazzoni S., Takacs, C.J., Cannell D.S., Giglio M., Nature communications 2, pp. 290, 2012
[3] Cerbino, R., Sun, Y., Donev, A. and Vailati A., Scientific Reports 5, pp. 14486, 2015
[4] F. Giavazzi, G. Savorana, A. Vailati, R. Cerbino, Soft Matter 12, pp. 6588, 2016
[5] Cerbino, R. and Trappe, V., Physical Review Letters, 100, pp. 188102, 2008
[6] Kirkpatrick, T.R, Ortiz de Zárate, J.M., Sengers J.V., Physical Review Letters 115, pp. 035901, 2015