title: Scaling behavior for the onset of convection in a colloidal suspension.
abstract: We investigate the early stages of mass convection in a colloidal suspension at high solutal Rayleigh number Ras. From the time evolution of shadowgraph images and by assuming a diffusive growth of the boundary layers we obtain an indirect measurement of the concentration boundary layer thickness delta* at the onset of convection. We show that the dimensionless boundary layer thickness delta=delta*/d scales as Ra-ps, where Ras=Rasdelta is a modified solutal Rayleigh number for convection which accounts for the actual density unbalance and d is the thickness of the sample layer. This scaling behavior is analogous to that reported at steady state for turbulent convection in simple fluids. We find p=0.35, a value compatible with the exponent 1/3, reported for turbulent heat convection in simple fluids at steady state.
authors.affiliation: Istituto Nazionale per la Fisica della Materia and Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Cerbino
authors.forename: Stefano
authors.initials: S
authors.lastname: Mazzoni
authors.forename: Alberto
authors.initials: A
authors.lastname: Vailati
authors.forename: Marzio
authors.initials: M
authors.lastname: Giglio