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Item type:Publication, Access status: without files , Colloidal growth of titania in nanoporous gold toward electrochemical applications(2022-10-20); ; ; Electrocatalytic water splitting for generating H2 necessitates engineering efficient electrocatalysts. Herein a simple colloidal approach for the colloidal growth of TiO2 in nanoporous gold (NPG), a sponge-like gold nanostructure composed of bi-continuous Au ligaments which can catalyze oxidation reactions, is shown. Partial to complete coverage of Au ligaments in NPG with TiO2 was achieved. The aliphatic chain length and critical micelle concentration of the surfactants were shown to influence the thickness and homogeneity of the TiO2 grown. Colloidal TiO2 growth within NPG could reduce the onset equilibrium potential of H2 evolution by ~68 % compared to pristine NPG, and increased the exchange current by 5.75 times over the latter. This straightforward colloidal approach will advance strategies for fabricating nanoporous hybrid materials where control over the surface coverage is pertinent to the performance of the composite.Publicationtype: Journal Article32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A continuous approach to the emulsion gelation method for the production of aerogel micro-particle(2019-04-05); ; Aerogel micro-particles have a wide range of applications demonstrated at lab-scale in numerous publications, but material in a larger amount needs to be produced to allow for industrial tests and prototyping. In this work, we propose a continuous emulsion-gelation process able to produce gel micro-particles in sizeable quantities, demonstrating the industrial relevance of such approach. Alginate is taken as a model gelling system and two gelation mechanisms are demonstrated. Alginate solution and oil are pumped together through a progressive cavity pump and fed to a colloid mill to produce alginate in oil emulsion in one pass. The gelation in emulsion is then carried in-line via a controlled injection of a gelation trigger (acetic acid or calcium chloride). The gel microparticles are separated from the oil via sedimentation or centrifugation and partitioning into an ethanol solution. Further solvent exchange to ethanol and supercritical drying with CO 2 yielded aerogel microparticles with large specific surface area. The size of the emulsion droplets is directly related to the final aerogel particles size. The influence of the emulsification parameters on the droplet size is thus discussed and assessed using critical capillary number values from the literature. To complete this task, the dynamic interfacial tension of the alginate-paraffin oil-Span80 system was measured and the rheology of the alginate solution and of the emulsion assessed.Publicationtype: Journal Article246 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mixed aqueous solutions of nonionic surfactants Brij 35/Triton X-100: Micellar properties, solutes' partitioning from micellar liquid chromatography and modelling with COSMOmicAqueous solutions of nonionic surfactants are of interest for bioprocesses, particularly as solubilizing agents for hydrophobic substances. To design such processes, the data on partition coefficients of solutes between micelles and their aqueous surrounding (Pmw) are of high value. An extended understanding of the partition behavior can be achieved from the structural information such as the micelle size and micelles composition. In this work, mixtures of nonionic surfactants Triton X-100 and Brij 35 were under study. The data on critical micelle concentrations showed partly non-ideal behavior of the solutions. The compositions of mixed micelles at different molar Brij 35/Triton X-100 ratios in the surfactant mixture were estimated from the data on self-diffusion coefficients (NMR diffusometry) and were calculated within the regular solution approach and predicted by Motomura's model. The change of the mixed micelle composition in dependence on the total surfactant concentration was observed. It has been found, that the average value of the mixed micelles radii is ∼4 nm. Whereas, the polydispersity indexes and the aggregation numbers increased with Triton X-100 fraction. Moreover, the Pmw values of different non-dissociated solutes (phenyl derivatives with various functional groups) were determined by means of micellar liquid chromatography (MLC) and were predicted using the thermodynamic model COSMOmic, an extension of COSMO-RS. In general, it has been proved that COSMOmic is able to predict Pmw in the mixed micellar system formed by nonionic surfactants. The obtained data show the possibility of modulating the partition behavior of solutes using the mixtures of nonionic surfactants. Apart from the hydrophobicity, the «surfactants – solute» specific interactions play an important role in the partition behavior of the investigated systems.Publicationtype: Journal Article171 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modelling foam improved oil recovery within a heterogeneous reservoir(2016-12-05); ; The displacement of foam within a heterogeneous reservoir during foam improved oil recovery is described with the pressure-driven growth model. The pressure-driven growth model has previously been used to study foam motion for homogeneous cases. Here the foam model is modified in such a way that it includes terms for variable permeability. This model gives the evolution of the foam motion over time and the shape of the foam front, a wet foam zone between liquid-filled and gas-filled zones. The foam front shape for a heterogeneous or stratified reservoir develops concave and convex regions. For shapes such as these, the numerical solution of pressure-driven growth requires special numerical techniques, particularly in the case where concavities arise. We also present some analysis of the level of heterogeneity and how it affects the displacement, the shape of the front developing a set of concave corners. In addition to this we consider a heterogeneous and isotropic reservoir, in which case the foam front can sustain concavities, without these concavities having the same tendency to develop into corners.Publicationtype: Journal Article21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Capillary rise dynamics of liquid hydrocarbons in mesoporous silica as explored by gravimetry, optical and neutron imaging: Nano-rheology and determination of pore size distributions from the shape of imbibition fronts(2016-05-05); ; ; ; We present combined gravimetrical, optical, and neutron imaging measurements of the capillarity-driven infiltration of mesoporous silica glass (Vycor) by hydrocarbons. Square-root-of-time Lucas-Washburn invasion kinetics are found for linear alkanes from n-decane (C10) to n-hexacontane (C60) and for squalane, a branched alkane, in porous monoliths with 6.5 nm or 10 nm mean pore diameter, respectively. Humidity-dependent experiments allow us to study the influence on the imbibition kinetics of water layers adsorbed on the pore walls. Except for the longest molecule studied, C60, the invasion kinetics can be described by bulk fluidity and bulk capillarity, provided we assume a sticking, pore-wall adsorbed boundary layer, i.e. a monolayer of water covered by a monolayer of flat-laying hydrocarbons. For C60, however, an enhanced imbibition speed compared to the value expected in the bulk is found. This suggests the onset of velocity slippage at the silica walls or a reduced shear viscosity due to the transition towards a behaviour typical of polymer-like flow in confined geometries. Both, light scattering and neutron imaging, indicate a pronounced roughening of the imbibition fronts. Their overall shape and increase in width can be resolved by neutron imaging. The fronts can be described by a superposition of independent wetting fronts moving with pore size-dependent square-root-of-time laws and weighted according to the pore size distributions obtained from nitrogen gas sorption isotherms. This finding indicates that the shape of the imbibition front in a porous medium, such as Vycor glass, with interconnected, elongated pores, is solely determined by independent movements of liquid menisci. These are dictated by the Young-Laplace pressure and hydraulic permeability variations and thus the pore size variation at the invasion front. Our results suggest that pore size distributions can be derived from the broadening characteristics of imbibition fronts.Publicationtype: Journal Article82 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Methane bubble rise velocities under deep-sea conditions—Influence of initial shape deformation(Elsevier, 2016-01-24); ; ; ; Terminal bubble rise velocities play a major role in industrial and environmental applications and the investigation of the rise velocities in different material systems and under different process conditions is of increasing interest. With respect to deep-sea oil spills and natural gas seeps, the investigation of methane bubble rise velocities under high-pressure and low-temperature conditions is of importance. In this context, near- and far-field models have been developed that use a group of correlations which is valid for contaminated systems. With these equations the velocities of bubbles and drops are calculated with the assumption of an immobilized particle interface, due to the existence of seawater and the possibility of hydrate formation. Experimental results under deep-sea conditions are very rare and often contradicting. To identify the physical processes which influence the rise behavior of methane bubbles under deep-sea conditions, laboratory experiments in a high-pressure vessel and under ambient conditions are conducted. Methane bubble rise velocities at 4 °C and 20 °C as well as 0.1 and 15.1 MPa are investigated in artificial seawater and demineralized water. Contrary to expectations, our experimental results under deep-sea conditions (4 °C, 15.1 MPa) show a brought distribution of the rise velocities for similar volume equivalent bubble diameters.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Foam stability in the presence and absence of hydrocarbons: From bubble- to bulk-scale(2015-09-01); ; One of the pioneering applications of foam is in enhanced oil recovery (EOR). A major stumbling-block to the success of foam application in EOR is the adverse influence of oil on foam stability. The objectives of the present work were to evaluate the effects of various surfactants and hydrocarbons with well-defined properties on foam stability. To do so, we have conducted a comprehensive series of experiments at bulk- and bubble-scale to investigate the foam stability of four surfactants in the absence and presence of three isoparaffins distinguished by their carbon chain length, density and viscosity. For the bulk foam stability experiments, foam was generated by sparging pure air into surfactant solution in a vertical cylindrical column. An automated camera was used to record the gradual decay of foam as a function of time. The results showed the significant impact of the type of the surfactant on foam stability. Besides, our results illustrated less stable foam in the presence of oil with less adverse impact on foam stability as oil viscosity and density increased. The limitation of the method used in the present study to quantify foam stability, i.e., measuring the decay of foam height over a certain period of time, which is a commonly used method in literature, is discussed here and an alternative approach is proposed to investigate foam stability at bubble-scale to supplement and improve understanding of the physical phenomena controlling foam stability.Publicationtype: Journal Article22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Foam improved oil recovery: Foam front displacement in the presence of slumping(2015-05-20); ; Foam is often used in improved oil recovery processes to displace oil from an underground reservoir. During the process, the reservoir is flooded with surfactant, and then gas is injected to produce foam in situ, with the foam front advancing through the reservoir. Here the effect of surfactant slumping (downward movement of surfactant in relation to a lighter phase) upon the advance of a foam front is presented. Slumping which can be associated with foam drainage, coarsening and collapse, causes a rise in mobility of the foam front specifically near the top of the front. The description of a foam front displacement for an initially homogeneous foam mobility is therefore modified to account for slumping-induced inhomogeneities. Numerical solution for the front shape shows that, although slumping transiently produces a localised concave region on the otherwise convex front, this concavity has little effect on the long term front evolution. In fact in the long-time limit, a convex kink develops on the front: an analytical solution describing the convex kink agrees very well with the numerics.Publicationtype: Journal Article18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Estimation of LPC/water partition coefficients using molecular modeling and micellar liquid chromatographyLysophosphatidylcholine (LPC) is a lipid based, micelle forming emulsifier and thus a potential solubilizer for hydrophobic components in pharmaceutical and food products. Since many components of interest are very hydrophobic, the determination of the partition equilibrium between the micelles and the aqueous bulk phase is challenging. In this work several methods (micellar liquid chromatography (MLC), molar solubilization ratio (MSR) and an indirect method, using an organic solvent phase) for the experimental determination of partition coefficients are compared. For the first time the emulsifier LPC was employed in the MLC. It is shown, that the partition coefficients between micelles and water can be determined with good agreement to literature data and between the different methods for solutes in a wide hydrophobicity range.Moreover, the experimental data are compared to a priori predictions based on the thermodynamic model COSMO-RS. The prediction assuming the pseudophase approach is compared to the prediction using COSMOmic, thus taking into account the anisotropic structure of the micelles, obtained from molecular dynamics all-atom simulations. Both methods agree well with the experimental data for the partition coefficients between LPC and water and between the anionic surfactant SDS and water. Using COSMOmic, beside the partition coefficient, the location of the solute within the micelle is predicted. It is shown, that the combination of experimental methods and models like COSMO-RS reveals a deeper understanding of the specific interactions, which is needed for an efficient use of emulsifiers in a variety of applications.Publicationtype: Journal Article67 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Wetting behavior at the free surface of a liquid gallium-bismuth alloy: An X-ray reflectivity study close to the bulk monotectic point(Elsevier, 2002-07-09); ; ; ; We present X-ray reflectivity measurements from the free surface of a liquid gallium-bismuth alloy (Ga-Bi) in the temperature range close to the bulk monotectic temperature Tmono=222°C. Our measurements indicate a continuous formation of a thick wetting film at the free surface of the binary system driven by the first order transition in the bulk at the monotectic point. We show that the behavior observed is that of a complete wetting at a tetra point of solid-liquid-liquid-vapor coexistence.Publicationtype: Journal Article16