Scaling of the spatial power spectrum of excitations at the onset of solutal convection in a nanofluid far from equilibrium.

We investigate pattern formation in the very early stages of solutal convective instabilities in a suspension of highly thermophilic nanoparticles heated from above. The processing of shadowgraph images allows us to recover the spatial power spectrum of the excitations at the onset. Remarkably, the power spectra obtained at large solutal Rayleigh numbers 2.56 x 10;{6}< or =Ra_{s}< or =4.53 x 10;{8} scale onto a single curve without adjustable parameters. The critical wave number exhibits power-law scaling with exponent 1/4 as a function of Ra_{s} , in excellent agreement with recent theoretical predictions.