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When in ambient air, the contact between an atomic force microscope tip and a sample is usually wetted due to the capillary condensation of water. This water layer affects both the normal force at the nanoasperity contacts by the effect of a meniscus loading force and the friction force by the meniscus kinetics. In this work, the influence of the water condensation, at the tip surface contact, on the friction force is studied for hydrophilic, partially hydrophilic, and hydrophobic surfaces. It is shown that the surface wettability plays an important role on the dependence of friction with the normal force and scanning velocity.

The use of chitosan biofilm in biomedical fields has a vast therapeutic potential due to useful properties such as biodegradability and antimicrobial activity, however, to achieve successful application some physicochemical properties need to be improved. In this context, the addition of glycerol to this biofilm is an alternative to improve its wettability and flexibility. Thus, low and high concentrations of plasticizer were added to this biomaterial for later characterization regarding its wettability, microstructure, mechanical and chemical properties. Glycerol addition to chitosan resulted in biofilms with more homogeneous surfaces, increased wettability, and increased flexibility, without significant changes in its chemical structure.