Imbibition and evaporation in model nanofluidic systems

Nanoporous media play a central role in many application fields (buildings, fuel cells, petroleum engineering, nuclear waste storage). At the nanometer scale, two-phase flows involve processes possibly modified when compared to macro (or even micrometer) scale: contact line pinning, wetting issues, strong negative pressure in the liquid and cavitation, gas dissolution and compression. We use nanofabrication technologies to assess simple situations such as evaporation, spontaneous imbibition, or drainage, in well-controlled artificial nanochannels. In particular, extremely high pressure differences (several tens bar) and surface/volume ratios lead to behaviors specific to the nanoscale. For imbibition, we observe a modified filling kinetics, and bubble trapping below a critical liquid-dependent dimension, of order 50 nm. Modeling shows pressurization of the gas phase, which has significant influence on gas dissolution and could thus be related to bubble occurrence. We also observe that confinement strongly controls qualitative behaviors, such as bubble nucleation and migration in evaporation, or corner flows during imbibition of closed-end rectangular geometries.