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The dynamic response of a polyvinylidene fluoride (PVDF) cantilever beam under excitation of water droplet impact is investigated by developing an electromechanical model. In the model, the governing equations of beam motion and output voltage are derived in the theoretical way, such that the voltage across the PVDF layer and the cantilever deflection can be predicted. The motion of the beam is described by the multi-mode vibration model through which more accurate results can be obtained. The predicted results of the model are validated by the experiment. Combined with the experiment and the model, the effect of surface wettability on droplet-substrate interaction mechanisms is investigated, which provides an insight into the improvement of mechanical-to-electrical energy conversion efficiency in raindrop energy harvesting (REH) applications. Results show: (1) the droplet splash on a super-hydrophobic beam surface has a positive effect on voltage generation. The splash limit that affects the reaction force of the impacting droplet is experimentally determined and greatly dominant by the Weber number. (2) Small-scaled droplets in splash regime allow generating higher voltage output from a super-hydrophobic beam surface than from an untreated hydrophilic beam surface. (3) Tests of successive droplet impacts also show that a super-hydrophobic surface performs better over a hydrophilic surface by producing constant peak voltage and higher electrical energy harvested. In this case, the voltage measured from the hydrophilic surface decreases gradually as the water layer is accumulated. Overall, the electromechanical behaviors of a super-hydrophobic PVDF cantilever sensor can be well predicted by the model which shows a great potential in energy harvesting by maximizing the inelastic collision upon droplet-substrate interactions.

Different γ-Ni/Mo 2 Ni 3 Si alloy coatings were fabricated on 0.45 wt-% C steel applying the DISTA300 semiconductor laser system. The microstructures, phase components and corrosion behaviour of the alloy coatings were investigated. Research results showed that lasercladded coatings with different compositions were all composed of ductile phase γ-Ni and reinforced phase Mo 2 Ni 3 Si. Electrochemical parameters and anodic polarisation curves revealed that the γ-Ni/Mo 2 Ni 3 Si alloy coatings exhibited a good corrosion performance in 3.5% NaCl solution in comparison with 0Cr18Ni9Ti stainless steel. The corrosion current density of the laser-cladded layer increased first and then decreased with the increasing volume fraction of Mo 2 Ni 3 Si. Moreover, the addition of Cr can significantly improve the passivation and anti-pitting ability of the γ-Ni/Mo 2 Ni 3 Si alloy coating.

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