Performance recovery of plasma actuators in wet conditions

Plasma actuators have been extensively studied for flow control applications. While these studies have been traditionally focused on characterizing their performances as flow control devices, the performance of plasma actuators under adverse conditions like light rain remains to be less explored. This paper seeks to study the effects of water adhesion from droplets directly sprayed on to a plasma actuator using thrust recovery as the performance metric. It was found in all tests that wet actuators quickly recover plasma glow, before gradually regaining performance comparable to the dry actuator. The measured thrust for the wet actuator after 5 seconds of operation recovered by 46% and 42% of the thrust of the dry actuator for 50.0-62.5 g/m2 and 125-150 g/m2 of sprayed water droplets, respectively. At 22.5 kVpp and 14 kHz, the highest thrust recovery was recorded at 84% of that of the dry actuator after 80 seconds of operation. For 17.5 kVpp and 14 kHz the wet thrust recovered by 79%, while for 22.5 kVpp and 10 kHz the wet thrust recovered by 68% of their dry counterpart in 80 seconds. For 17.5 kVpp and 14 kHz, the thrust almost fully recovered in comparison to the dry actuator after about 290 seconds of operation. These results indicate that both applied voltage and operating frequency plays a critical role in the performance recovery while the latter may have a stronger influence. Performance recovery for a wet serpentine shaped plasma actuator is also included for general applicability. The power data in all cases show that wet actuators consume more power which with time gradually approach the dry actuator power data. This because during the initial stages of operation, the rolling mean current of the wet actuator is higher than the dry actuator even though the ionization spikes of dry actuator is stronger.

Halloysite nanotubes-based nanocomposites for the hydrophobization of hydraulic mortar

The treatment of stone surfaces for their protection from ageing caused by natural and anthropogenic effects is an open issue in materials development for Cultural Heritage. We thought interesting to verify the suitability of a modified cellulose biofilm filled with halloysite nanotubes as wax compatibilizers to design a protecting layer. A hydraulic mortar was selected as a stone prototype. To improve the physico-chemical properties of the covering layer, wax microparticles have been incorporated to control transport, consolidation and wettability features. In particular, different application protocols have been studied, namely brushing and spraying, to assess whether the proposed procedures can be scaled up. Colorimetric analysis has been carried out to evidence the applicability in terms of color alteration after the treatment. Water adhesion was investigated by measuring the contact angle values as a function of time to obtain information on spreading and adsorption phenomena. These physico-chemical properties have been correlated to the microstructure evidenced by both electron and optical microscopies. Graphic abstract

Highly conjugated carbazole-based monomers for the control of nanotubular surface structures by soft template electropolymerization

In this work, a bioinspired approach is used to prepare nanotubular structures with tunable hydrophobicity and water adhesion by a soft template surfactant-free electropolymerization in organic solvent. Various highly conjugated carbazole-based molecules are used as monomer. The presence of water in the organic solvent enables the formation of porous and rough nanostructures. Their shapes depend essentially on the nature of the monomer and the way it polymerizes. Various morphologies were obtained from nanoparticles network to horizontally or vertically aligned nanotubes. The nanostructured surfaces reach superhydrophobic properties and their dynamical behavior varies with the monomer from sticky to slippery. For example, using 9,3′:6′,9″-tercarbazole (TC) very long nanotubes are observed but their number is higher at constant potential. At high deposition charge, it is observed that most of the tubes are even collapsed leading to a strong increase of surface hydrophobicity with apparent contact angle up to 143° with strong water adhesion comparable to rose petals or gecko foot.