The modification of the wetting properties of marble surfaces by a biomimetic laser processing approach has been investigated. Marble surfaces have been irradiated with ultrashort laser pulses in different conditions to analyze the effect of laser treatment on their wetting properties with the aim of evaluating its potential for surface protection. The contact angle of a water drop placed on the surface was used to assess the wettability of the processed areas versus the pristine surface. Although the surfaces are initially hydrophilic upon laser treatment, after a few days they develop a strong hydrophobic behavior. The time evolution of the contact angle has been monitored up to 11 months after treatment. A short and a long-term evolution, associated to the combined effect of multi-scale roughness (nano- and micro-roughness) and the attachment of chemical species at the surface over the time, has been observed. Through an analysis of the temporal evolution of surfaces processed with different laser scan line separations, the relative roles of multi-scale roughness and chemical changes has been elucidated and correlated to the induced morphologies. Micro-roughness manifests as a noticeable micro-scale topography modulation, leading to a hydrophobic behavior consistent with the Cassie-Baxter model. In turn, the superimposed nano-roughness leads to an increase of the effective surface area, enhancing the attachment of chemical functional groups over time that progressively modify the surface energy. The durability of the improved surface properties (hydrophobicity) has been tested by measurements of the contact angle of the stabilized (aged) surfaces after cleaning in different conditions with very positive results.
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