Abstract
We investigate the early stages of mass convection in a colloidal suspension at high solutal Rayleigh number R a^ s. 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 δ* at the onset of convection. We show that the dimensionless boundary layer thickness δ= δ*/d scales as R a s− p, where R a s= R a^ s δ 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.
Roberto Cerbino
Professor of Experimental Soft Matter Physics
My research interests include Soft matter physics, living matter, cell biophysics and quantitative microscopy.