Equilibrium fluctuations of thermodynamic variables, such as density or concentration, are known to be small and typically occur at a molecular length scale. In contrast, theory predicts that non-equilibrium fluctuations grow very large both in amplitude and spatial size. On earth, the presence of gravity and buoyancy forces severely limits the development of the fluctuations. We will present the results of a 14-year long international collaboration on an experiment on non-equilibrium fluctuations in a single liquid and in a polymer solution under microgravity conditions. Non-equilibrium conditions are generated by applying a temperature gradient across millimetre-size liquid slabs. Phase modulations introduced by fluctuations are measured using a quantitative shadowgraph method, with the optical axis parallel to the temperature gradient. Thousands of images are analysed and their two-dimensional power spectra yield the fluctuation structure function S(q), once data are reduced accounting for the instrumental transfer function T(q). The mean-squared amplitude of the fluctuations exhibits an impressive power-law dependence at larger q and a crossover at low q showing that the fluctuation size is limited by the sample thickness. The shape of the structure function, its increase due to removing gravity, and its dependence on applied gradient are in reasonable agreement with available theoretical predictions.

Gradient-driven fluctuations in microgravity / A. Vailati, R. Cerbino, S. Mazzoni, M. Giglio, C. J. Takacs, D. S. Cannell. - In: JOURNAL OF PHYSICS. CONDENSED MATTER. - ISSN 0953-8984. - 24:28(2012 Jun 27), pp. 284134.284134.1-284134.284134.10. ((Intervento presentato al 8. convegno Liquid Matter Conference tenutosi a Wien nel 2011.

Gradient-driven fluctuations in microgravity

A. Vailati;R. Cerbino;M. Giglio;
2012-06-27

Abstract

Equilibrium fluctuations of thermodynamic variables, such as density or concentration, are known to be small and typically occur at a molecular length scale. In contrast, theory predicts that non-equilibrium fluctuations grow very large both in amplitude and spatial size. On earth, the presence of gravity and buoyancy forces severely limits the development of the fluctuations. We will present the results of a 14-year long international collaboration on an experiment on non-equilibrium fluctuations in a single liquid and in a polymer solution under microgravity conditions. Non-equilibrium conditions are generated by applying a temperature gradient across millimetre-size liquid slabs. Phase modulations introduced by fluctuations are measured using a quantitative shadowgraph method, with the optical axis parallel to the temperature gradient. Thousands of images are analysed and their two-dimensional power spectra yield the fluctuation structure function S(q), once data are reduced accounting for the instrumental transfer function T(q). The mean-squared amplitude of the fluctuations exhibits an impressive power-law dependence at larger q and a crossover at low q showing that the fluctuation size is limited by the sample thickness. The shape of the structure function, its increase due to removing gravity, and its dependence on applied gradient are in reasonable agreement with available theoretical predictions.
diffusion ; fluctuations ; microgravity ; optical techniques ; nonequlibrium
Settore FIS/07 - Fisica Applicata(Beni Culturali, Ambientali, Biol.e Medicin)
Settore FIS/03 - Fisica della Materia
JOURNAL OF PHYSICS. CONDENSED MATTER
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/204727
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