Wettability and corrosion of [NTf2] anion-based ionic liquids on steel and PVD (TiN, CrN, ZrN) coatings

Thewetting and corrosion behavior of three bis(trifluoromethylsulfonyl)imide-based ionic liquids: 1-Dodecyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide [C12MIM][NTf2], tributylmethylammonium bis(trifluoromethylsulfonyl)imide [N4441][NTf2] and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide [N1888][NTf2] are tested in this research. The surface tension was measured for temperatures of 293–353 K resulting in the expected linearly decreasing behavior with temperature increase. In addition, contact angle measurements were made on AISI 52100 steel and three coatings (TiN, CrN and ZrN) obtained by PVD technique, finding the regular behavior in hydrophobic (non-polar) systems: high contact angles led to high surface tensions. Complementary parameters like spreading parameter and polarity fraction were calculated to enhance the wetting evaluation of these ionic liquids. [N1888][NTf2]/TiN resulted as the best IL-surface combination for a good wettability, due to the higher dispersion of the charge on the large size cation in this IL and the higher values of total and polar component of the surface free energy for this coating. Finally, SEM-EDS analysis determined that [N1888][NTf2]/ZrN was the best option in order to avoid corrosion problems. The evaporation of water, present as impurity in the ionic liquids, was found the main reason because of corrosion did not occur in the tests carried out at 100 °C

Electrowetting: Electrocapillarity, saturation, and dynamics

Electrowetting is an electrocapillary phenomenon, i.e. the surface charge generated at the solid-liquid interface through an external voltage improves the wettability in the system. The Young-Lippmann equation provides the simplest thermodynamic framework and describes electrowetting adequately. Saturation, i.e. the reduced or nullified effectiveness of the external voltage below a threshold contact angle value, was and remains the most controversial issue in the physics of electrowetting. A simple estimation of the limits of validity of the Young model is obtained by setting the solid-liquid interfacial tension to zero. This approach predicts acceptably the change in electrowetting mechanism but not the minimal value of the contact angle achievable during electrowetting. The mechanism of saturation is, in all probability, related to charge injection into the dielectric layer insulating the working electrode but physical details are scarce. Surface force and spectroscopic techniques should be deployed in order to improve our understanding of the surface charging of insulators immersed in conductive liquids. Electrowetting in solid-liquid-liquid systems is generally more effective and robust. Electrowetting offers new ways of studying the dynamics of liquid movement as it allows selective changes in the wettability of the system

Obituary: Tharwat F. Tadros

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The influence of topography on dynamic wetting

The paramount importance of wetting applications and the significant economic value of controlling wetting-based industrial processes has stimulated a deep interest in wetting science. In many industrial applications the motion of a complex liquid front over nano-textured surfaces controls the fate of the processes. However our knowledge of the impact of nano-heterogeneities on static and dynamic wetting is very limited. In this article, the fundamentals of wetting are briefly reviewed, with a particular focus on hysteresis and roughness issues. Present knowledge and models of dynamic wetting on smooth and rough surfaces are then examined, with particular attention devoted to the case of nano-topographical heterogeneities and solid-fluid-fluid systems

Yielding and fracturing of concentrated emulsions in narrow gaps

We used rheology and confocal microscopy techniques to characterise the flow of emulsions as the droplets were confined by increasing the drop volume fraction and reducing the distance between the shearing surfaces. Slip was minimised by matching the density of the oil and water phases. Attractive interactions between the drops caused them to flocculate. The contribution of the emulsion microstructure to its shear response becomes significant when the oil drop flocs almost span the distance between the surfaces. We found that confining the flow of droplet flocs causes a transition from a fluid phase with shear thinning flow behaviour into a jammed, solid-like material. The large deformations caused by flow at the maximum drop packing fraction induce droplet coalescence within highly localised regions of the emulsion

A comparative study on the removal of methyl isobutyl carbinol from froth flotation circuits by chemical treatment

Residual frother accumulation is a growing problem in coal and mineral processing plants due to the increased need for water recycling to meet environmental regulations and cost management. The presence of accumulated frother downstream from flotation circuits promotes foam generation in process units such as pumps and cyclones causing cavitation and in severe cases can lead to plant froth out and shut down. It is therefore highly desirable to determine an appropriate method to remove the frother from the process water downstream of the flotation circuit to prevent accumulation of residual frother and avoid the associated problems. This project aimed to identify and evaluate methods of controlling the level of one of the most commonly used surfactants for frothing applications, methyl isobutyl carbinol (MIBC). Performance was assessed by comparing the steady-state foam heights before and after chemical treatment using Bikerman's method to generate foam. Three reagents that are readily available in industry were examined; ozone, sodium hydroxide and sulfuric acid. Although all three reagents successfully reduced the foam height and hence frother concentration, ozone was found to be up to 200 times more effective than either sodium hydroxide or sulfuric acid. Furthermore, both sodium hydroxide and sulfuric acid were rejected as feasible industrial solutions due to the large quantities required. Therefore, an industrial solution using ozone could be a viable solution with minimal capital and operating costs involved in implementation.Alex Perndt, Jason Connor, Rossen Sedev and Yung Ngotha