Geosequestration of carbon dioxide in basaltic rock formations is considered to have the potential to safely and permanently store significant quantities of this greenhouse gas and thereby mitigate its potential global warming effect. The success of this storage method is primarily dependent on the wettability behaviour of the rock-waterCO2 system, which significantly affects fluid distribution, fluid transport, storage capacity and containment security. This study investigates the wettability performance of several Western Australian altered basaltic rocks, of similar geochemistry, porosity and inter-connection. The wettability behaviour of the basaltic materials is assessed using water containing ions that have been leached from the rock samples used in this investigation (Synthetic Formational Water). Under realistic geo-storage conditions, most samples exhibited intermediate -wet behaviour at pressures of 10 to 80 bar and a temperature of 50 degrees C. Further increase in pressure from 80 to 100 bar at 50 degrees C changed the wettability of the altered basaltic rock samples with most samples changing from an intermediate-wet state to weakly CO2-wet state, while the other sample maintained this intermediate-wet at 100 bar and 50 degrees C temperature. This study highlights the potential of Western Australian altered basaltic rocks to be used for the mineral storage of CO2.

Hydrogen geo-storage could be the large-scale solution needed for a hydrogen economy. Biological factors have been considered but mainly in terms of hydrogen-metabolising microbes. We demonstrate consistently the direct influence of underground biofilm formation on the wettability of sandstone reservoirs. The biofilm, formed by incubation with cyanobacteria Geitlerinema sp. in seawater, increases the advancing and receding brine contact angles on water-wet quartz. The angles decrease only slightly on oil-wet quartz surfaces even though biomass accumulation is more significant. We formulate an explanation using Cassie's approach to heterogeneous surfaces, taking into account the predominant surface chemical groups. Wettability strongly affects the distribution, trapping and mobility of phases (brine and hydrogen) inside the rock formation. Our results, obtained at typical reservoir conditions (25-50 degrees C, 3-130 bar), are relevant to understanding and assessing hydrogen injectivity, withdrawal rates, storage capacity and containment security. This fundamental research supports the development of an industrial-scale decarbonized hydrogen economy.

Hydrogen is expected to play a significant role as a clean energy carrier. However, the development of a hydrogen economy requires the use of large amounts of hydrogen; therefore, large-scale hydrogen storage is a considerable problem that needs to be resolved. Hydrogen can be stored underground in aquifers, salt caverns, depleted oil and gas reservoirs, and coal seams. In this context, wettability is a critical parameter in determining the containment security, storage capacity, fluid dynamics, and withdrawal rate during underground hydrogen geo-storage operations. Meanwhile, the toxic soluble dye, methyl orange (MO), is widely used in the textile and other industries and released in large quantities into the surface and subsurface waters. Hence, in the present study, the use of MO to alter the wettability of reservoirs in favor of hydrogen geo-storage is investigated. To this end, model oil-wet rock surfaces are prepared by aging quartz substrates with stearic acid and then treating them with various amounts of aqueous MO for 1 week at 50 degrees C. The brine contact angles on these model surfaces are then measured in a hydrogen environment under various reservoir conditions to demonstrate that the MO treatment makes the surface more hydrophilic. Moreover, the contact angle is seen to increase significantly with the increase in the temperature, pressure, and salinity. In addition, the importance of pH is assessed, and various brines (NaCl, KCl, MgCl2, and CaCl2) are compared. The proposed treatment is expected to improve the hydrogen trapping efficiency of sandstone reservoirs while simultaneously providing a safe disposal route for MO via deep well injection.

A microbubble air flotation technique was used to remove chromium ions from simulated wastewater (e.g. water used for electroplating, textiles, paints and pigments, and tanning leather). Experimental parameters were investigated to analyze the flotation process and determine the removal efficiency. These parameters included the location of the sampling port from the bottom of the column, where the diffuser is located to the top of flotation column (30, 60, and 90 cm), the type of surfactant (anionic, SDS, or cationic, CTAB) and its concentration (5, 10, 15, and 20 mg/L), the pH of the initial solution (3, 5, 7, 9, and 11), the initial contaminant concentration (10, 20, 30, and 40 mg/L), the gas flow rate (0.1, 0.2, 0.3, and 0.5 L/min), and the contact time (5, 10, 15, 20, 25, 30, and 35 min). The experimental results revealed that the highest removal efficiency (95%) was achieved in 20 min with a pH of 7, a flow rate of air 0.5 L/min, an SDS surfactant concentration of 15 mg/L, and a pollutant concentration of 30 mg/L at a sampling port height of 30 cm. The use of microbubbles in comparison to normal bubbles, resulted in a 56% improvement of the removal efficiency. The flotation process follows a first-order kinetics.

This study focuses on the wettability alteration (changing from a hydrophobic state to a hydrophilic state) of Indiana limestone for hydrogen (H2) geological storage. We examine the effect of hexanoic acid C6, lauric acid C12, and stearic acid C18, on the wettability of Indiana limestone at ambient (298 K and 0.1 MPa) and reservoir (323 K and 8.27 MPa) conditions. The effects of silica nanofluids (silica with deionized water) at various concentrations (0.1 wt%, 0.25 wt%, and 0.5 wt%) on the wettability reversal of stearic-aged samples were tested at ambient and reservoir conditions. The results revealed increased H2-wetness (hydrophobicity) of the rock exposed to these organic acids in reservoir conditions. However, this hydrophobicity significantly decreased with the nanofluid treatment of the stearic-aged samples. This wettability reversal may increase the H2 storage capacity and containment security and lead to successful large-scale geological storage operations if H2 residual trapping is minimized. (c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Hydrogen storage is a main issue in the establishment of a hydrogen economy. Geo‐storage could be a viable solution if hydrogen could be injected into and withdrawn from suitable geological formations, reversibly and reliably. Rock wettability is a major factor as it affects injectivities, withdrawal rates, storage capacities, and containment security. We report here the contact angles of a brine on the surface of a bituminous coal in a pressurized hydrogen atmosphere. Under realistic geo‐storage conditions the coal surface was weakly water‐wet. Hydrogen pressure increased brine contact angles at 25°C but did not have an impact at 50 or 70°C. We present a thermodynamic model that describes the observed behavior. Our results would support the development of large‐scale geo‐storage technologies for hydrogen.

A high-pressure microfluidic platform was used to mix an organic solution with carbon dioxide. Complete mixing occurred on board the microchip and allowed controlled precipitation of active pharmaceutical ingredients (APIs). Griseofulvin was precipitated from dimethylformamide with a tuneable particle size varying between 0.5 and 500 mu m. The particle size increased with API concentration (favorable crystal growth) and decreased with driving pressure (efficient mixing promoting nucleation). Two different micromixers were used: CO2 flowing into the solution from a side channel (T-junction) and CO2 entering the mixing channel flanked by two liquid streams (X-junction). Systematically smaller particles were obtained with the T-junction micromixer because of the higher antisolvent concentration. The process can be carried out continuously with good control over the operating parameters. It is a step in the miniaturization and process intensification of gas antisolvent precipitation with opportunities for micronizing APIs.

Halloysite clay nanotubes are efficient biocompatible nanocarriers for pharmaceutical products. A gas antisolvent (GAS) process employing subcritical carbon dioxide delivers a product with high loading (43 %) and free of residual solvent. An anticancer agent, 5-fluorouracil, was loaded on nanoclay particles. A quantitative distinction is made between tightly-bound (adsorbed) and loosely-bound (co-precipitated) drug. The physical stages of the dense gas process are clearly outlined. The strongly attached drug is released completely at pH - 7.4 but only up to 30 % in pH = 1.2. The release follows first-order kinetics with a characteristic time of 2 h. The mass ratio of clay nanotubes to 5-fluorouracil affects the loading with adsorbed drug as well as the ratio of loose to tightly attached drug molecules. The system Halloysite-5-fluorouracil can be implemented in drug delivery systems to achieve a desired release profile. The GAS process is a one-pot green process with a low solvent consumption and high-purity product. (C) 2020 Elsevier B.V. All rights reserved.

Microfluidic flow in lab-on-a-chip devices is typically very sensitive to the variable physical properties of complex samples, e.g., biological fluids. Here, evaporation-driven fluid transport (transpiration) is achieved in a configuration that is insensitive to interfacial tension, salinity, and viscosity over a wide range. Micropillar arrays ("pillar cuvettes") were preloaded by wicking a known volatile fluid (water) and then adding a microliter sample of salt, surfactant, sugar, or saliva solution to the loading zone. As the preloaded fluid evaporates, the sample is reliably drawn from a reservoir through the pillar array at a rate defined by the evaporation of the preloaded fluid (typically nL/s). Including a reagent in the preloaded fluid allows photometric reactions to take place at the boundary between the two fluids. In this configuration, a photometric signal enhancement is observed and chemical analysis is independent of both humidity and temperature. The ability to reliably transport and sense an analyte in microliter volumes without concern over salt, surfactant, viscosity (in part), humidity, and temperature is a remarkable advantage for analytical purposes.

Surface-inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil-in-water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil-water interfaces when repulsive forces between particles and oil droplets are suppressed. The emulsifying efficiency of the highly hydrophilic particles is determined by van der Waals attraction between particle monolayer shells and oil droplets enclosed therein and is inversely proportional to the particle size, while their stabilizing efficiency is determined by van der Waals attraction between single particles and oil droplets, which is proportional to the particle size. This differentiation in mechanism between emulsification and stabilization will significantly advance our knowledge of emulsions, thus enabling better control and design of emulsion-based technologies in practice.

The characteristic angle measured through the droplet phase between the solid-liquid interface interfacial control of multiphase fluids in miniaturized devices and the plane of the liquid-vapor interface at the contact line is referred to as the contact angle and is the most common measure of wettability. This chapter focuses on the interplay of geometry and chemistry in determining wetting behavior and the implications for passive control of fluids in microfluidic systems where immiscible fluids meet. The chapter reviews the fundamentals of surface wettability with respect to ideal and nonideal surfaces, metastable wetting behavior, and wetting dynamics. It describes several approaches to modifying microchannel wettability and discusses several key applications of wetting in microfluidic devices and structures. These include wetting-controlled spontaneous filling, valving, flow stability, phase separation, and the role of wettability in droplet (or bubble)-based microfluidics.

Froth flotation is a key pre-concentration process in many minerals processing operations and also in wastewater treatment. At its heart is the interaction between micrometer-sized particles and air bubbles. An understanding of the factors affecting such interactions can be used to enhance process optimization. Al- though instruments such as the atomic force microscope and surface force apparatus have been used to explore these interactions, they are limited by the mechanical constraint placed on the particle and the sensitivity to stronger short-range ( In this paper we give the first-ever report of force -vs- distance measurements using optical tweezers of the interactions between air bubbles and micrometer-sized silica spheres across a range of electrolyte solutions. In addition to force profiles, adhesive forces of the bubble-particle systems were also measured and found to increase significantly with increasing salt concentration. To benchmark the experimental procedure we also measured forces between a silica sphere and a glass fibre. The results were compared with calculations based on DLVO theory and found to be in qualitative agreement.

The wetting of a material can be tuned by changing the roughness on its surface. Recent advances in the field of nanotechnology open exciting opportunities to control macroscopic wetting behaviour. Yet, the benchmark theories used to describe the wettability of macroscopically rough surfaces fail to fully describe the wetting behaviour of systems with topographical features at the nanoscale. To shed light on the events occurring at the nanoscale we have utilised model gradient substrata where surface nanotopography was tailored in a controlled and robust manner. The intrinsic wettability of the coatings was varied from hydrophilic to hydrophobic. The measured water contact angle could not be described by the classical theories. We developed an empirical model that effectively captures the experimental data, and further enables us to predict the wetting of surfaces with nanoscale roughness by considering the physical and chemical properties of the material. The fundamental insights presented here are important for the rational design of advanced materials having tailored surface nanotopography with predictable wettability.

Solvent extraction of rare earth elements (REEs) involves hundreds of individual extraction and phase separation cycles, fine adjustment of solution conditions, and individual stage and overall process times that are long. Therefore, we investigated microfluidic solvent extraction (microSX) of REEs from a leached mixed rare earth oxide (REO) mineral concentrate using a phosphorus-based cationic exchange extractant (Cyanex® 572). A Y–Y microchip was used, in which the aqueous and organic phases were contacted for up to 15s with sub-second resolution. The extraction rate and selectivity for heavy REEs was determined for the prepared leach solution. Good selectivity for heavy REEs was observed using the microchip for leach solutions adjusted to pH 0.7. Extraction rates on the microchip were typically double that observed in conventional (bulk) solvent extractions, except for Lu and Yb, which were three-times faster. The faster extraction can be largely attributed to the higher surface-to-volume ratio achieved in our microfluidic experiments; double that observed for bulk extractions under the conditions employed.

Liquid marbles are liquid droplets covered densely with small particles. They exhibit hydrophobic properties even on hydrophilic surfaces and this behaviour is closely related to the Cassie wetting state and the phenomenon of superhydrophobicity. Typical liquid marbles are of millimetre size but their properties are analogous to smaller capsules and droplets of Pickering emulsions. We study water marbles covered with an uneven multilayer of polyethylene particles. Their elastic properties were assessed under quasi-static conditions. The liquid marbles are highly elastic and can sustain a reversible deformation of up to 30%. The spring constant is of the same order of magnitude as that for bare water droplets. Therefore the elasticity of the liquid marble is provided mainly by the liquid menisci between the particles. Upon further compression, the spring constant increases up to the point of breakage. This increase may be due to capillary attraction acting across the emerging cracks in the particle coating. The stress-strain curve for liquid marbles is similar to that obtained with liquid-filled microcapsules. A mechanical scaling description proposed for capsules is qualitatively applicable for liquid marbles. The exact mechanical role of the multilayer particle network remains elusive.

The molecular-kinetic theory (MKT) of dynamic wetting was formulated almost 50years ago. It explains the dependence of the dynamic contact angle on the speed of a moving meniscus by estimating the non-hydrodynamic dissipation in the contact line. Over the years it has been refined to account explicitly for the influence of (bulk) fluid viscosity and it has been applied successfully to both solid–liquid–vapour and solid–liquid–liquid systems. The free energy barrier for surface diffusion has been related to the energy of adhesion. The MKT provides a qualitative explanation for most effects in dynamic wetting. The theory is simple, flexible, and it is widely used to rationalize the physics of wetting dynamics and fit experimental data (dynamic contact angle versus contact line speed). The MKT predicts an intermediate wettability as optimal for high-speed coating as well as the maximum speeds of wetting and dewetting. Nevertheless, the values of the molecular parameters derived from experimental data tend to be scattered and not particularly reliable. This review outlines the main achievements and limitations of the MKT and highlights some common cases of misinterpretation.