When an air bubble or an oil droplet in a nanofluid (liquid containing dispersed nanoparticles) approaches a solid surface, a nanofluid film is formed between the bubble or drop and a solid ...substrate. The nanoparticles confined in the film surfaces tend to self-layer and the film thins in a stepwise manner. The wetting behavior and film stability criteria valid for the classical molecularly thin films cannot be applied to nanofilm. Here we present an overview of the structure and stability of multilayer nanofilms wetting solid surfaces. We first present a brief review of the classical concept of molecular films wetting solid, and then we discuss the nanofluid film structure evolution as determined by the in-layer radial distribution function versus nanofilm's number of layers. The role of the particle volume fraction, size and polydispersity on the layering phenomenon is highlighted. The stability of the nanofilm, that is its layer-by-layer thinning is elucidated by the presence of particle voids or dislocations. We calculated the free energy of the nanofilm on a solid surface based on nanofilm osmotic pressure. We independently verified it by the direct measurement of the nanofilm-meniscus contact angle using reflected light interferometry. Finally, we present some practical applications of a wetting aqueous film for oily soil removal from a solid surface and the nanofilm displacing an oil phase from a capillary as in an enhanced oil recovery operation.
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•Nanofilm structure on solid was probed by in-layer Radial Distribution Function.•Mechanism of film stability and stepwise thinning are revealed.•Evaluation of the film-meniscus contact angle and thickness are presented.•Two approaches to estimate the film free energy are discussed and verified.•Applications of nanofilm wetting solid are presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Colloidal nano altered wetting is an everyday phenomenon with various applications. It occurs when an aqueous colloidal droplet is placed on a wet solid and evaporates with a pinned contact line (to ...form a shape similar to a coffee ring) and when a ‘superspreader’ is placed on a partially wet solid surface with an unpinned contact line. This article reviews recent advances on the mechanisms behind these two phenomena. For the coffee ring phenomenon, besides the evaporation flow, the thermal and solutal Marangoni flow are critical to the radial flow as they carry solutes from the droplet's interior to the contact line. The particle self-assembly into a layered structure at the droplet edge involves particle structuring under confinement and the stagnation flow. While superspreading is not fully understood, it is proposed that the Marangoni flow plays an essential role in superspreading.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Top view depicting the movement of the outer and inner contact lines with time in the pre-equilibrated oil/polymeric nanofluid on the glass substrate. Display omitted
Nanofluids comprising ...nanoparticle suspensions in liquids have significant industrial applications. Prior work performed in our laboratory on the spreading of an aqueous film containing nanoparticles displacing an oil droplet has clearly revealed that the structural disjoining pressure arises due to the layering of the nanoparticles normal to the confining plane of the film with the wedge profile. The pressure drives the nanofluid in the wedge film and the nanofluid spreads. We observed two distinct contact lines: the inner contact line, where the structural disjoining pressure dominates the Laplace capillary pressure, and the outer contact line, given by the Laplace equation prediction extrapolated to the solid substrate where the structural disjoining pressure contribution is negligible. We report here our results of the effects of several parameters, such as the nanoparticle concentration, liquid salinity, temperature, and the substrate contact angle, on the motion of the two contact lines and their effects on the detachment of the oil droplet. We also studied the equilibrated and non-equilibrated oil/nanofluid phases, the time of adhesion of the oil droplet on the solid substrate and the drying time of the substrate. We employed the frictional model to predict the outer contact line velocity and our previous theoretical model (based on the structural disjoining pressure) to predict the inner contact line velocity. The theoretical predictions agreed quite well with the experimentally measured values of the velocities.
Our experimental results showed that the motion of the inner contact line was accelerated by the increase in the nanoparticle concentration, temperature, and hydrophilicity of the substrate for the pre-equilibrated oil/nanofluid phases, which resulted in the faster detachment of the oil droplet. The speed of the two contact lines decreased upon the increase in the drying time of the substrate and the oil adhesion time on the substrate.
The present results provide new insights into the complex spreading behavior of nanofluids on solid substrates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The classical Lucas–Washburn–Rideal (LWR) equation, using the equilibrium contact angle, predicts a faster capillary rise process than experiments in many cases. The major contributor to the faster ...prediction is believed to be the velocity dependent dynamic contact angle. In this work, we investigated the dynamic contact angle models for their ability to correct the dynamic contact angle effect in the capillary rise process. We conducted capillary rise experiments of various wetting liquids in borosilicate glass capillaries and compared the model predictions with our experimental data. The results show that the LWR equations modified by the molecular kinetic theory and hydrodynamic model provide good predictions on the capillary rise of all the testing liquids with fitting parameters, while the one modified by Joos’ empirical equation works for specific liquids, such as silicone oils. The LWR equation modified by molecular self-layering model predicts well the capillary rise of carbon tetrachloride, octamethylcyclotetrasiloxane, and n-alkanes with the molecular diameter or measured solvation force data. The molecular self-layering model modified LWR equation also has good predictions on the capillary rise of silicone oils covering a wide range of bulk viscosities with the same key parameter W(0), which results from the molecular self-layering. The advantage of the molecular self-layering model over the other models reveals the importance of the layered molecularly thin wetting film ahead of the main meniscus in the energy dissipation associated with dynamic contact angle. The analysis of the capillary rise of silicone oils with a wide range of bulk viscosities provides new insights into the capillary dynamics of polymer melts.
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IJS, KILJ, NUK, PNG, UL, UM
Magnesium-based hydrogen storage alloys have attracted significant attention as promising materials for solid-state hydrogen storage due to their high hydrogen storage capacity, abundant reserves, ...low cost, and reversibility. However, the widespread application of these alloys is hindered by several challenges, including slow hydrogen absorption/desorption kinetics, high thermodynamic stability of magnesium hydride, and limited cycle life. This comprehensive review provides an in-depth overview of the recent advances in magnesium-based hydrogen storage alloys, covering their fundamental properties, synthesis methods, modification strategies, hydrogen storage performance, and potential applications. The review discusses the thermodynamic and kinetic properties of magnesium-based alloys, as well as the effects of alloying, nanostructuring, and surface modification on their hydrogen storage performance. The hydrogen absorption/desorption properties of different magnesium-based alloy systems are compared, and the influence of various modification strategies on these properties is examined. The review also explores the potential applications of magnesium-based hydrogen storage alloys, including mobile and stationary hydrogen storage, rechargeable batteries, and thermal energy storage. Finally, the current challenges and future research directions in this field are discussed, highlighting the need for fundamental understanding of hydrogen storage mechanisms, development of novel alloy compositions, optimization of modification strategies, integration of magnesium-based alloys into hydrogen storage systems, and collaboration between academia and industry.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Magnesium-based hydrogen storage materials have garnered significant attention due to their high hydrogen storage capacity, abundance, and low cost. However, the slow kinetics and high desorption ...temperature of magnesium hydride hinder its practical application. Various preparation methods have been developed to improve the hydrogen storage properties of magnesium-based materials. This review comprehensively summarizes the recent advances in the preparation methods of magnesium-based hydrogen storage materials, including mechanical ball milling, methanol-wrapped chemical vapor deposition, plasma-assisted ball milling, organic ligand-assisted synthesis, and other emerging methods. The principles, processes, key parameters, and modification strategies of each method are discussed in detail, along with representative research cases. Furthermore, the advantages and disadvantages of different preparation methods are compared and evaluated, and their influence on hydrogen storage properties is analyzed. The practical application potential of these methods is also assessed, considering factors such as hydrogen storage performance, scalability, and cost-effectiveness. Finally, the existing challenges and future research directions in this field are outlined, emphasizing the need for further development of high-performance and cost-effective magnesium-based hydrogen storage materials for clean energy applications. This review provides valuable insights and references for researchers working on the development of advanced magnesium-based hydrogen storage technologies.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
CeO2 is an important rare earth (RE) oxide and has served as a typical oxygen storage material in practical applications. In the present study, the oxygen storage capacity (OSC) of CeO2 was enhanced ...by doping with other rare earth ions (RE, RE = Yb, Y, Sm and La). A series of Undoped and RE–doped CeO2 with different doping levels were synthesized using a solvothermal method following a subsequent calcination process, in which just Ce(NO3)3∙6H2O, RE(NO3)3∙nH2O, ethylene glycol and water were used as raw materials. Surprisingly, the Undoped CeO2 was proved to be a porous material with a multilayered special morphology without any additional templates in this work. The lattice parameters of CeO2 were refined by the least–squares method with highly pure NaCl as the internal standard for peak position calibrations, and the solubility limits of RE ions into CeO2 were determined; the amounts of reducible–reoxidizable Cen+ ions were estimated by fitting the Ce 3d core–levels XPS spectra; the non–stoichiometric oxygen vacancy (VO) defects of CeO2 were analyzed qualitatively and quantitatively by O 1s XPS fitting and Raman scattering; and the OSC was quantified by the amount of H2 consumption per gram of CeO2 based on hydrogen temperature programmed reduction (H2–TPR) measurements. The maximum OSC of CeO2 appeared at 5 mol.% Yb–, 4 mol.% Y–, 4 mol.% Sm– and 7 mol.% La–doping with the values of 0.444, 0.387, 0.352 and 0.380 mmol H2/g by an increase of 93.04, 68.26, 53.04 and 65.22%. Moreover, the dominant factor for promoting the OSC of RE–doped CeO2 was analyzed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A cubic fluorite-type CeO2 with mesoporous multilayered morphology was synthesized by the solvothermal method followed by calcination in air, and its oxygen storage capacity (OSC) was quantified by ...the amount of O2 consumption per gram of CeO2 based on hydrogen temperature programmed reduction (H2–TPR) measurements. Doping CeO2 with ytterbium (Yb) and nitrogen (N) ions proved to be an effective route to improving its OSC in this work. The OSC of undoped CeO2 was 0.115 mmol O2/g and reached as high as 0.222 mmol O2/g upon the addition of 5 mol.% Yb(NO3)3∙5H2O, further enhanced to 0.274 mmol O2/g with the introduction of 20 mol.% triethanolamine. Both the introductions of Yb cations and N anions into the CeO2 lattice were conducive to the formation of more non-stoichiometric oxygen vacancy (VO) defects and reducible–reoxidizable Cen+ ions. To determine the structure performance relationships, the partial least squares method was employed to construct two linear functions for the doping level vs. lattice parameter and VO vs. OSC/SBET.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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Surfactant solutions containing polymeric nanoparticles have been shown to have an improved wetting and spreading on solid surfaces. In this work, we explored the effect of the ...polymeric nanoparticles on the frictional coefficient at the three-phase contact region by studying polymeric nanofluids displacing oil in capillaries. Our results show polymeric nanoparticles can reduce the frictional coefficient by as much as four times by forming structured layers in the confined wedge film. We also demonstrate the role of the interfacial tension in affecting the frictional coefficient.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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The rise of the main meniscus in rectangular capillaries is important in interpreting the phenomenon of fluid flow in porous media. Despite many experimental studies reported in the ...literature, there is no universal model for the rise of the main meniscus in either rectangular or square capillaries. In this work, we present an extensive experimental study and modeling of the rise of the main meniscus in both square and rectangular capillaries. Experimental work was carried out using three different liquids (water, ethanol, and hexadecane) in borosilicate glass and plastic (polystyrene) capillaries to investigate the effect of the contact angle and capillary size on the equilibrium main meniscus height. A universal model (an extended two-wall model) based on the Laplace equation was developed to predict the equilibrium height of the main meniscus in rectangular capillaries. Results have shown that, in a wide range of capillary sizes and contact angles, the predicted equilibrium heights of the main meniscus are in good agreement with the experimentally measured values.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
