Capillary Rise and Flow of Complex Liquids in Nanopores

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We propose to study the flow of complex liquids in monolithic, porous silica glasses and porous silicon (mean pore diameter d = 10nm) as a function of the size and shape of the building blocks of the liquids and the applied shear rates. In particular, we would like to compare flow rate measurements taken in a membrane flow apparatus with measurements on the spontaneous imbibition, that is the capillary rise in the pores driven by capillary forces. Whereas the flow apparatus measurements will allow us to determine the viscosities of the nanoconfined liquids, the filling process of the capillary rise crucially depends not only on the viscous drag but also on the capillary pressure acting in the nanopores. In order to vary the complexity of the liquids we suggest to measure liquids built out of chain-like (n-alkanes), rod-like and disc-like (liquid crystals) molecules - all of them with molecular sizes on the order of the diameter of the nanopores. The experimental study will shed light on the question to what extend continuum-like, macroscopic fluid behavior is valid down to nano-scopic lenght scales.