How water wets and self-hydrophilizes nanopatterns of physisorbed hydrocarbons

Hypothesis: Weakly bound, physisorbed hydrocarbons could in principle provide a similar water-repellency as obtained by chemisorption of strongly bound hydrophobic molecules at surfaces. Experiments: Here we present experiments and computer simulations on the wetting behaviour 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. Findings: 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.

Subjects

Atomic force microscopy

Electron microscopy

Molecular dynamics simulation

n-Alkane

Silica

Silicon

Wetting

DDC Class

600: Technik

Funding(s)

GRK 2462: Teilprojekt B1 Selbstdiffusion und Transport von molekularen Flüssigkeiten in granularen Packungen aus mesoporösen Silikat- und Aerogel-Pulvern

SFB 986: Teilprojekt B7 - Polymere in grenzflächenbestimmten Geometrien: Struktur, Dynamik und Funktion an planaren und in porösen Hybridsystemen

SFB 986: Teilprojekt B10 - Funktionalisierung von hierarchischen nanoporösen Metallen durch aktive organische Filme

DASHH Helmholtz Graduiertenkolleg

Funding Organisations

Deutsche Forschungsgemeinschaft (DFG)

More Funding Information

UGV acknowledges support of Fondecyt 1180939. TPC acknowledges the support of Fondecyt Iniciación 11160664, PCI MPG190023. PH acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) within the priority program SPP 2171, “Dynamic wetting of flexible, adaptive and switchable surfaces”, Projektnummer 22879465.

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How water wets and self-hydrophilizes nanopatterns of physisorbed hydrocarbons