Impact of nanoscale morphology on the IsoElectric Point of nanostructured surfaces

We study how surface nanoscale roughness and morphology affect the charging behaviour of nanostructured surfaces (titania, zirconia) in aqueous electrolytes. The charging behavior of surfaces has important consequences for nanoparticle adsorption processes, as in the case of cell or protein-surface interactions, as well as for the behaviour of photo-electrochemical and catalytic devices.

We use AFM in force spectroscopy mode, equipped with colloidal probes, to characterise the IsoElectric Point (IEP) of surfaces. The use of a colloidal probe provides well-defined interaction geometry, and allows effectively probing the overall effect of nanoscale morphology.

By using supersonic cluster beam deposition (SCBD) to fabricate nanostructured films, we achieve a quantitative control over the surface morphological parameters, which is mandatory in order to perform a systematical exploration of the electrical double layer properties in different interaction regimes, characterized by different ratios of characteristic nanometric lengths of the system: the surface rms roughness, the correlation length, and the Debye length.

Our main result is the observation of a remarkable reduction by several pH units of the IEP on rough nanostructured surfaces, with respect to flat samples.

Referent: Alessandro Podestà

Participants: Francesca Borghi