| Abstract |
Superhydrophobic surfaces, which display water contact angles larger than 150°,
have attracted a significant scientific interest due to their importance in both
fundamental research and practical applications; the existence of a hierarchical
surface roughness in conjunction with the appropriate chemical composition are the
critical parameters that define the behavior. The objective of the current work was to
fabricate a superhydrophobic surface in a simple, fast and economical way that needs
minimum demands regarding the necessary equipment and methods. The material
used was a smooth Ti6Al4V metal alloy that is widely used in several applications
whereas its surface is considered hydrophilic. The surface of the material was initially
irradiated, without following a specific pattern, by a femtosecond (fs) laser, in order to
acquire the necessary roughness. Following the irradiation, the effect of different
parameters like temperature, pressure as well as residence time under heating or
vacuum on the surface properties was investigated and the results were compared to
the respective ones of a smooth surface. Contact angle measurement were performed
in all cases, using a contact angle goniometer (OCA 35), to evaluate the water contact
angle as well as the contact angle hysteresis. The surface morphology was imaged by
scanning electron microscopy (SEM) whereas the surface chemical composition was
evaluated by the method of energy dispersive X-Ray spectroscopy (EDS). A surface
that has been just irradiated was found to possess superhydrophillic properties,
nevertheless its residence in an oven at different temperatures results in an alteration
of its surface characteristics and in the manifestation of a hydrophobic behavior
exhibiting a contact angle of 149 ± 2° especially for temperatures higher than 120°. A similar effect was observed in the case that an irradiated surface was placed in the
vacuum chamber (pressure 10-2 mbar);after a minimum of 3 hours the surface was
converted to a superhydrophobic one with a contact angle of 149 ± 1°. Moreover,
surfaces that remain under vacuum possess water repellent properties exhibiting a
very low contact angle hysteresis as well. The observed behavior can be understood if
one considers the change in the surface morphology and surface chemical
composition.
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Development of functional material surfaces
