Functionalization of metal surfaces by laser micro-machining and their potential for tribological and rheological applications

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Nature gives plenty of striking examples of sophisticated solutions to typical engineering problems such as wetting, drag and friction. The interesting functionalities of all these surfaces can be traced back to one common feature: a surface structure on two length scales (on the micro- and nanometer scale). Femtosecond laser micromachining is a high precision, microfabrication technique, which allows the fabrication of surface structures on two length scales in one process step. The goal of the proposed research is to use this process on metals, polymers and ceramics to biomimic various natural surfaces with superior functionalities for engineering applications. The influence of various laser settings and the effect of the irradiation environment will be studied with regard to the resulting surface structure and reactivity. It is expected that the surface wettability of the irradiated sample can be controlled through the surface geometry and timely exposure of the reactive surface to a well defined environment. Tribological studies will focus on the hypothesis that (i) hydrophobicity reduces capillary attraction in the presence of relative humidity; (ii) surface valleys act as traps for wear debris; and (iii) the hierarchical surface structure serves as lubricant reservoirs. Finally, flow studies will address slip flow enhancement through superhydrophobic, air trapping surface structures. The proposed research is original in two important aspects: (1) It constitutes a one-step process to structure and functionalize surfaces of various materials by non-contact micromachining, which offers high precision in the resulting structure, versatility with regard to the geometries that can be treated, and is easy to upscale for commercial applications. (2) It opens the door to conduct fundamental research aimed at investigating the isolated effect of surface wettability on anti-fouling, anti-icing, tribological and rheological studies without changing the underlying base material - something that has not yet been possible. The initial projects of this research program will involve the training of two M.Eng. and two Ph.D. students over the next 5 years. Future HQP training will exceed this number, indicating the great research potential of this new field.