Superhydrophobic Cerium-Based Coatings on Al-Mg Alloys and Aluminized Steel

Aluminum-magnesium (Al-Mg) alloy and aluminum-coated steel (aluminized steel) are typically used for the manufacturing of baking trays and molds. For these applications, these materials must be modified to develop release and hydrophobic properties. With this aim, the bare substrates are typically coated with low-surface energy materials such as fluoropolymers, elastomers, or sol-gel layers. In this work, some alternative strategies to prepare these functional surfaces are presented. We used three-step processes involving (i) micro-texturing, (ii) nano layer deposition through immersion and electrodeposition, and (iii) hydrophobization. The raw substrates were sanded or sandblasted at the micro scale, accordingly. Texturization at the nano scale was achieved with a cerium layer formed by electrodeposition or solution immersion. The cerium layers were hydrophobized with fatty acids. The wetting properties of the samples were studied with tilting-plate and bouncing drop methods. We measured the surface roughness of the samples by contact profiling and analyzed their surface morphology using a field emission scanning electron microscope (FESEM). The elemental chemical composition of the samples was analyzed by energy-dispersive X-ray spectroscopy (EDX). The wettability results indicated that the best performance for the Al-Mg substrates was reached by sandblasting and later immersion in a cerium nitrate solution. For aluminized steel substrates, the best results were obtained with both electrodeposition and immersion methods using a cerium chloride solution

RICORS2040 : The need for collaborative research in chronic kidney disease

Chronic kidney disease (CKD) is a silent and poorly known killer. The current concept of CKD is relatively young and uptake by the public, physicians and health authorities is not widespread. Physicians still confuse CKD with chronic kidney insufficiency or failure. For the wider public and health authorities, CKD evokes kidney replacement therapy (KRT). In Spain, the prevalence of KRT is 0.13%. Thus health authorities may consider CKD a non-issue: very few persons eventually need KRT and, for those in whom kidneys fail, the problem is 'solved' by dialysis or kidney transplantation. However, KRT is the tip of the iceberg in the burden of CKD. The main burden of CKD is accelerated ageing and premature death. The cut-off points for kidney function and kidney damage indexes that define CKD also mark an increased risk for all-cause premature death. CKD is the most prevalent risk factor for lethal coronavirus disease 2019 (COVID-19) and the factor that most increases the risk of death in COVID-19, after old age. Men and women undergoing KRT still have an annual mortality that is 10- to 100-fold higher than similar-age peers, and life expectancy is shortened by ~40 years for young persons on dialysis and by 15 years for young persons with a functioning kidney graft. CKD is expected to become the fifth greatest global cause of death by 2040 and the second greatest cause of death in Spain before the end of the century, a time when one in four Spaniards will have CKD. However, by 2022, CKD will become the only top-15 global predicted cause of death that is not supported by a dedicated well-funded Centres for Biomedical Research (CIBER) network structure in Spain. Realizing the underestimation of the CKD burden of disease by health authorities, the Decade of the Kidney initiative for 2020-2030 was launched by the American Association of Kidney Patients and the European Kidney Health Alliance. Leading Spanish kidney researchers grouped in the kidney collaborative research network Red de Investigación Renal have now applied for the Redes de Investigación Cooperativa Orientadas a Resultados en Salud (RICORS) call for collaborative research in Spain with the support of the Spanish Society of Nephrology, Federación Nacional de Asociaciones para la Lucha Contra las Enfermedades del Riñón and ONT: RICORS2040 aims to prevent the dire predictions for the global 2040 burden of CKD from becoming true

Electric double-layer potentials and surface regulation properties measured by colloidal-probe atomic force microscopy

We show how the colloidal-probe technique, which is based on force measurements made with the atomic force microscope, can be used to accurately determine the charging parameters of water-solid interfaces. Besides yielding accurate values of the double-layer or diffuse-layer potential, the method also allows reliable determination of the charge regulation properties of the surfaces. The latter can be quantified with a regulation parameter, which is essential to properly describe forces between interfaces, especially in asymmetric situations when one of the interfaces is charged and the other one is close to neutral. The technique relies on a highly charged probe particle, for which the charging properties are accurately determined by interpreting the double-layer contribution of the measured force profiles in the symmetric sphere-sphere geometry with Poisson-Boltzmann (PB) theory. Once the probe particle is calibrated, this particle is used to measure the force profile between an unknown substrate in the asymmetric sphere-sphere or sphere-plane geometry. From this profile, the diffuse-layer potential and regulation parameter of the substrate can be again determined with PB theory. The technique is highly versatile, as it can be used for a wide variety of substrates, including colloidal particles and planar substrates. The technique is also applicable in salt solutions containing multivalent ions. The current drawbacks of the technique are that it can only be applied up to moderately high salt levels, typically to 10 mM, and only for relatively large particles, typically down to about 1 μm in diameter. How the technique could be extended to higher salt levels and smaller particle size is also briefly discussed

Forces between different latex particles in aqueous electrolyte solutions measured with the colloidal probe technique

In this article, a compilation of resul ts on direct force measurements between colloidal particles in monovalent salts carried out with the colloidal probe technique based on Atomic Force Microscopy was presented. The interaction forces between similar and dissimilar particles was studied and it was concluded that, in general, these force profiles may be satisfacto- rily quantified by the DLVO theory down to distances of few nanometers. However, in the specific case where the charge of one of the involved particle is close to neutral, it was found that the sur- face potential of this particle may change its sign depending on the sign of charge of the opposite particle. In this respect, the assumption that the s urface potential of a particle is a property only related to the particle surface features and th e bul k prop ert ies is called int o que s tion

Accurate Predictions of Forces in the Presence of Multivalent Ions by Poisson–Boltzmann Theory

Forces between positively and negatively charged colloidal particles across aqueous salt solutions containing multivalent ions are measured directly with the atomic force microscope (AFM). The measurements are interpreted quantitatively with Poisson–Boltzmann (PB) theory. Thereby, the surface potentials and regulation properties of the particle surfaces are extracted from symmetric measurements between the same types of particles. This information is used to predict force profiles in the asymmetric situations involving different types of particles without any adjustable parameters. These predictions turn out to be very accurate, which demonstrates that the mean-field PB theory is reliable down to distances of about 5 nm. While various reports in the literature indicate that this theory should fail due to neglect of ion correlations, such effects seem important only at higher concentrations and smaller distances

Measurements of dispersion forces between colloidal latex particles with the atomic force microscope and comparison with Lifshitz theory

Interaction forces between carboxylate colloidal latex particles of about 2 μm in diameter immersed in aqueous solutions of monovalent salts were measured with the colloidal probe technique, which is based on the atomic force microscope. We have systematically varied the ionic strength, the type of salt, and also the surface charge densities of the particles through changes in the solution pH. Based on these measurements, we have accurately measured the dispersion forces acting between the particles and estimated the apparent Hamaker constant to be (2.0 ± 0.5) × 10−21 J at a separation distance of about 10 nm. This value is basically independent of the salt concentration and the type of salt. Good agreement with Lifshitz theory is found when roughness effects are taken into account. The combination of retardation and roughness effects reduces the value of the apparent Hamaker constant and its ionic strength dependence with respect to the case of ideally smooth surfaces

Long-ranged and soft interactions between charged colloidal particles induced by multivalent coions

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Attractive Forces between Charged Colloidal Particles Induced by Multivalent Ions Revealed by Confronting Aggregation and Direct Force Measurements

Interactions involving charged particles in the presence of multivalent ions are relevant in wide-range of phenomena, including condensation of nucleic acids, cement hardening, or water treatment. Here, we study such interactions by combining direct force measurements with atomic force microscopy (AFM) and aggregation studies with time-resolved light scattering for particles originating from the same colloidal suspension for the first time. Classical DLVO theory is found to be only applicable for monovalent and divalent ions. For ions of higher valence, charge inversion and additional non-DLVO attractive forces are observed. These attractive forces can be attributed to surface charge heterogeneities, which leads to stability ratios that are calculated from direct force measurements to be higher than the experimental ones. Ion–ion correlations are equally important as they induce the charge inversion in the presence of trivalent or tetravalent ions, and they enhance the surface charge heterogeneities. Such heterogeneities therefore play an essential role in controlling interactions in particle suspensions containing multivalent ions

Specific Ion Effects and pH Dependence on the Interaction Forces between Polystyrene Particles

Colloidal interactions have been extensively studied due to the wide number of applications where colloids are present. In general, the electric double layer force and the van der Waals interaction dominate the net force acting between two colloids at large separation distances. However, it is well accepted that some other phenomena, especially those acting at short separation distances, might be relevant and induce substantial changes in the force profiles. Within these phenomena, those related to the surface contact angle, the hydration degree of the ions, or the pH, may dominate the force profiles features, not only at short distances. In this paper, we analyzed the effect of the pH and counterion type on the long-range as well as short-range forces between polystyrene colloidal particles by using the colloidal probe technique based on AFM. Our results confirm that the features of the force profiles between polystyrene surfaces are strongly affected by the pH and hydration degree of the counterions in solution. Additionally, we performed a study of the role of the pH on the wettability properties of hydrated and nonhydrated polystyrene sheets to scan the wettability properties of this material with pH. Contact angle measurements confirmed that the polystyrene surface is hydrophobic in aqueous solutions over the entire range of pHs investigated. These results are in good agreement with the features observed in the force profiles at low pH. At high pH, a short-range repulsion similar to the one observed for hydrophilic materials is observed. This repulsion scales with the pH, and it also depends on the hydration degree of the ions in solution. This way, the short-range forces between polystyrene surfaces may be tunable with the pH, and its origin does not seem to be related to the hydrophobicity of the material