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 2.56×10<6Ras<4.53×108 scale onto a single curve without adjustable parameters. The critical wave number exhibits power-law scaling with exponent 1/4 as a function of Ras, in excellent agreement with recent theoretical predictions.