  Weakly bound, physisorbed hydrocarbons could in principle provide a similar
water-repellency as obtained by chemisorption of strongly bound hydrophobic
molecules at surfaces. Here we present experiments and computer simulations on
the wetting behavior of water on molecularly thin, self-assembled alkane
carpets of dotriacontane (n-C32H66 or C32) physisorbed on the hydrophilic
native oxide layer of silicon surfaces during dip-coating from a binary alkane
solution. By changing the dip-coating velocity we control the initial C32
surface coverage and achieve distinct film morphologies, encompassing
homogeneous coatings with self-organised nanopatterns that range from dendritic
nano-islands to stripes. These patterns exhibit a good water wettability even
though the carpets are initially prepared with a high coverage of hydrophobic
alkane molecules. Using in-liquid atomic force microscopy, along with molecular
dynamics simulations, we trace this to a rearrangement of the alkane layers
upon contact with water. This restructuring is correlated to the morphology of
the C32 coatings, i.e. their fractal dimension. Water molecules displace to a
large extent the first adsorbed alkane monolayer and thereby reduce the
hydrophobic C32 surface coverage. Thus, our experiments evidence that water
molecules can very effectively hydrophilize initially hydrophobic surfaces that
consist of weakly bound hydrocarbon carpets.
