The fabrication of aqueous bitumen emulsions requires the presence of surface-active molecules to minimize interfacial energy. The natural surfactants present in bitumen, especially those belonging to the asphaltene fraction, play an important role, but hydrophilic synthetic surfactants are also added to promote the formation of the desired oil-in-water emulsion. We demonstrated, in a previous paper (Jatav, S.; Bouriat, P.; Anaclet, P.; Hung, Y.; Rondelez, F.; Dicharry, C. Proceedings of the RILEM ISBM 2020, 2022, 27, 1635), that these two types of surfactants, endogenous and exogenous, compete for adsorption onto the interface, which can be detrimental for the long-term stability of the emulsion. In the present work, we studied two different bitumens A and B with opposite emulsion-forming behaviors and used the "wet silica chromatography method" (Jarvis, J.M.; Robbins, W.K.; Corilo, Y.E.; Rodgers, R.P. Energy & Fuels, 2015, 29 (11), 7058) to separate their endogenous surfactants into two categories, referred to as the extracted fraction and the eluted fraction. The viscoelastic and tensiometric properties of these systems diluted with Heptol 10 (a 50 vol % mixture of n-heptane and toluene) were investigated using interfacial shear rheology (ISR) and surface tensiometry (IFT). Our measurements revealed that the extracted endogenous surfactants are the main contributors to the high elastic and viscous moduli necessary to ensure the long-term mechanical stability of the bitumen emulsions. A higher proportion of extracted endogenous surfactants adsorbed at the interface, to the detriment of eluted endogenous surfactants, correlates with greater stability of bitumen emulsions. In addition, our data showed that the extracted endogenous surfactants have to compete with the exogenous surfactants when they first reach the interface and rapidly displace them. These two requirements are fulfilled better in the case of bitumen A than in the case of bitumen B.

Introduction : Ces dernières années, le développement de biomatériaux à faible impact environnemental a attiré un intérêt croissant. Dans ce contexte, les nanoparticules lipidiques ont émergé comme une solution privilégiée dans la recherche et l'industrie. L'objectif de cette étude était de mettre au point des émulsions Pickering O/W stabilisées exclusivement par des nanoparticules lipidiques solides (SLNs). Ces émulsions de Pickering sont une nouvelle génération de transporteurs lipidiques, à la fois sûrs, non toxiques, biocompatibles et sensibles à la température. Matériel et Méthodes : La première partie de l'étude se concentre sur la compréhension du comportement interfacial des SLNs et les mécanismes de stabilisation associés aux nanoémulsions formulées par ultrasons. Les recherches ont exploré la couverture de surface en fonction des fractions volumiques des phases dispersées et de la taille des SLNs. La deuxième partie de l'étude aborde l'adsorption des SLNs à une interface modèle entre l'huile et l'eau, en évaluant la tension superficielle et la rhéologie. Cela a été réalisé au moyen d'une analyse de la forme d'une goutte axi-symétrique (à l'aide d'un tensiomètre de goutte), en suivant l'évolution de la tension interfaciale et du comportement rhéologique. Résultats : Ces expériences ont démontré de manière concluante que la stabilisation des nanogouttelettes est effectivement assurée par les nanoparticules, tout en mettant en lumière les limites de cette formulation. La caractérisation des dimensions et de la morphologie des émulsions a permis de confirmer nos hypothèses. Par ailleurs, nous avons procédé à la caractérisation du phénomène régissant les interactions entre les nanogouttelettes et l'interface, tout en décrivant le comportement rhéologique de la monocouche de SLNs à l'interface. Conclusion : En conclusion, les émulsions de Pickering stabilisées par les SLNs se révèlent être des nano-transporteurs de médicaments innovants et très efficaces. Elles ouvrent ainsi de nouvelles perspectives en tant que système de délivrance de médicaments sensible à la température.

Unprecedented massive growth of fibrous cyclopentane hydrate on an activated carbon was shown recently to circumvent the mass-transfer bottleneck caused by hydrate crust at guest-host interfaces. Here, we generalize to other carbons and to porous silicas, confirming hydrate formation in surface macropores. Experiments with hydrophilic or -phobic porous substrates and with single glass capillary model pores elucidate the growth process. Surprisingly, wettability is of indirect importance. Detailed observation of unlimited single fibers with the better optical access and well-defined geometry of the glass model pores reveals the growth mechanism: crystal dewetting at pinned guest-host interfaces, in surface macropores in the case of porous substrates, where hydrophobicity serves only indirectly, to conduct the guest to the active interface. Fiber growth is closely analogous to the dewetted Bridgman process observed decades ago in microgravity. "Micro" or negligible gravity is provided here by the small size of the pores compared to the capillary length. Transposing the theory to the present system, we correlate fiber diameter and dynamic contact angles on the fiber and the pore wall, which in turn depend on the growth rate, hence on the supercooling. The model prescribes for generalization to further combinations of guest and porous substrates.

Bitumen-in-water emulsions are often used for paving applications but some of them lack long-term stability. The relative importance of the cationic surfactant added to the aqueous phase to favor emulsification and the endogenous ones contained in bitumen is investigated by measuring the visco-elastic properties of three different bitumen-water interfaces as a function of time. We observe that the long-term emulsion stability correlates well with high values of the interfacial storage (G′) and loss (G″) moduli. Since these parameters become significantly weaker when an emulsamine cationic surfactant is added to water, we emphasize that the use of exogenous surfactants may be detrimental to long-term emulsion stability from interfacial behavior point of view.

In this work, we used an original experimental setup to examine the behavior of insoluble monolayers made with pH-sensitive lipids. Two kinds of unsaturated lipids were chosen: a cationic one (lipid 1) bearing an ammonium headgroup and an anionic one (lipid 2) terminated with an acidic phenol group. The lipids were deposited onto an air bubble interface maintained in an aqueous phase and, after stabilization, were subjected to a series of compressions performed at different pH values. These experiments disclosed a gradual increase in the specific area per molecule when lipids were neutralized. Imposing a pH variation at constant bubble volume also provided surface pressure profiles that confirmed this molecular behavior. As complementary characterization, dilatational rheology disclosed a phase transition from a purely elastic monophasic system to a viscoelastic two-phase system. We hypothesized that this unexpected increase in the specific area with lipid neutralization is related to the presence of unsaturations in each of the two branches of the hydrophobic tails that induce disorder, thereby increasing the molecular area at the interface. Application of the two-dimensional Volmer equation of state allowed the generation of quantitative values for the specific areas that showed variations with pH. It also allowed the determination of apparent pKa values, which are affected by both the electrostatic potential within the monolayer and the affinity of the lipid polar head for the aqueous phase.

Glass micro-capillaries are the simplest yet most versatile, robust, practical and cheap microfluidic devices.Their small size and high optical quality favour detailed investigation under the optical microscope.Here we first review some of their applications, such as determining contact angles and the observation of tenuous wetting films under harsh conditions of pressure and temperature.We further explore how an optical cusp formed by reflection off the inner wall of a glass capillary may be used to monitor the refractive index of its fluid content.Finally, we illustrate how the above advantages may be put to use in the study of extremophile microorganisms, for example in recreating under the microscope the conditions prevailing on the ocean floors. RÉSUMÉ :Les microcapillaires de verre sont les outils microfluidiques les plus simples, et né anmoins ils sont polyvalents, robustes et bon marché .Leur petite taille et grande qualité optique favorisent leur utilisation sous le microscope optique.Nous passons en revue quelques unes de leurs applications, comme la dé termination d'angles de contact et l'observation de films de mouillage en conditions sé vè res de pression et tempé rature.Nous explorons ensuite comment la caustique formé e par ré flexion sur la paroi interne du capillaire est relié e à l'indice de ré fraction du contenu fluide.Finalement, nous illustrons comment ces avantages peuvent servir à l'é tude d'organismes extré mophiles, par exemple en recré ant sous le microscope les conditions des fonds océ aniques.

We study the effects of hydrodynamic forces in frequency-modulation AFM experiments (FM-AFM) in liquid. We first establish the theoretical equations needed to derive the interaction stiffness k int and the damping β int due to the hydrodynamic forces from the frequency shift and the excitation amplitude. We develop specific FM-AFM experiments to measure the variation of k int and β int over a large range of distance in water up to 200 µm. Comparison between theory and experiments point out that the evolution of k int at short and long distance arises from unsteady hydrodynamic forces on the cantilever. On the other hand, β int is small at long distance and diverges at short probe-surface distance, as predicted by the classical Reynolds sphere model.

Correction for ‘Pickering nano-emulsions stabilized by solid lipid nanoparticles as a temperature sensitive drug delivery system’ by Sidy Mouhamed Dieng et al., Soft Matter, 2019, DOI: 10.1039/c9sm01283d.

The development of biomaterials with low environmental impact has seen increased interest in recent years. In this field, lipid nanoparticles have found a privileged place in research and industry. The purpose of this study was to develop Pickering O/W nano-emulsions only stabilized by solid lipid nanoparticles (SLNs), as a new generation of safe, non-toxic, biocompatible, and temperature-sensitive lipid nano-carriers. The first part is dedicated to understanding the interfacial behavior of SLNs and their related stabilization mechanisms onto nano-emulsions formulated by ultrasonication. Investigations were focused on the surface coverage as a function of the SLN size and volume fraction of dispersed oil, in order to prove that the droplet stabilization is effectively performed by the nanoparticles, and to disclose the limitations of this formulation. Characterization is performed by dynamic light scattering and transmission electron microscopy. The second part of the study investigated SLN adsorption on a model oil/water interface (surface tension and rheology) through an axisymmetrical drop shape analysis (drop tensiometer), following the interfacial tension and the rheological behavior. The objective of this part is to characterize the phenomenon governing the droplet/interface interactions, and disclose the rheological behavior of the interfacial SLN monolayer. The effect of temperature was also investigated, proving a real destabilization of the nano-suspension when the sample is heated above a temperature threshold, impacting on the integrity of the SLNs, which partially melt, and strongly enhancing the release of a model drug (ketoprofen) encapsulated in the nano-emulsion oil core. To conclude, Pickering nano-emulsions only stabilized by SLNs appear to be a very efficient innovative drug nano-carrier, opening new doors as a potential temperature-sensitive drug delivery system.

This comment defends the view that asphaltenes, when adsorbed at oil/water interfaces, are able to self-associate to form larger area spanning aggregates that explains the gel-like behavior generally observed with dilatational rheology, against the picture of Banerjee & Pauchard who represent asphaltene-laden interfaces as ideal monolayers of asphaltenes obeying the Langmuir equation of state with dilatational rheology given by the Lucassen van den Tempel model. It is shown that their model leads on overestimated surface density for asphaltenes molecules and that the correct interpretation of their data by mean of Frumkin model with a large repulsive interaction parameter is an evidence that interfacial aggregation occurs in an asphaltene layer located at oil/water interface.

A novel anaerobic fermentative bacterium, strain SEBR 4209(T), was isolated from a water sample of a Congolese oil field. Strain SEBR 4209(T) is phylogenetically related to the genus Pleomorphochaeta, in the family Spirochaetaceae. Its closest relatives are Pleomorphochaeta caudata SEBR 4223(T) (94.5 % 16S rRNA gene sequence similarity) and Pleomorphochaeta multiformis MO-SPC21 (94.3 % similarity). Like the other members of this genus, cells have a pleomorphic morphology, in particular an annular shape and long stalks. Optimal growth was observed at 37 degrees C, at pH between 6.8 and 7.0, and with 40 g l(-1) NaCl. This strain was only able to grow by fermentation of carbohydrates. The fermentation products from glucose utilization were acetate, ethanol, CO2 and H-2. Predominant fatty acids were C-14:0, C-14:0 DMA, C-1(6:)0 and C-1(6):(1)omega 7c. The major polar lipids were phosphoglycolipids, phospholipids and glycolipids. The G+C content of the DNA was 29.6 mol%. Based on phenotypic characteristics and phylogenetic traits, strain SEBR 4209(T) is considered to represent a novel species of the genus Pleomorphochaeta, for which the name Pleomorphochaeta naphthae sp. nov. is proposed. The type strain is SEBR 4209(T) (=DSM 104684(T)=JCM 31871(T)).

Expanding the electrical double layer of minerals through low-salinity brine injection has been suggested as a possible enhanced oil recovery mechanism. To investigate this theory, we measured the potential of different minerals, namely, sands from Fontainebleau, Ottawa, and Landes, a sample from a sandstone outcrop, and one crude oil. c-potential measurements can be used to quantify the surface charges of materials; therefore, experiments associated with this technique were performed to predict the behavior of repulsion or attraction between materials in different salinity and pH conditions. We showed that there is no significant difference between the xi potentials of the tested materials. We did, however, observe that the different sands and sandstone have dissimilar adhesion behaviors. No correlation was found between the electrokinetic measurements performed on the minerals and their response to crude oil introduced into the system. The adhesion results obtained for the Landes and Ottawa sands were perfectly in line with what was expected from xi-potential measurements, but the Fontainebleau sand and sandstone exhibited different behaviors. For the tested minerals, we showed that xi-potential changes may not be only responsible for a low-salinity brine effect concerning a system oil/brine/rock systematically characterized in a coreflood with an observed additional recovery.

We design and implement a simple and versatile droplet-based millifluidic method for investigating nucleation and growth processes in crystal-forming aqueous systems. It consists in generating and storing in a transparent capillary a train of identical and regularly-spaced droplets of an aqueous phase in a carrier oil phase, and then in video-monitoring crystal nucleation and subsequent growth and melting events as temperature and/or pressure are varied. Compared to previous investigations, the novelty is the possibility of working with aqueous solutions containing dissolved gas under controlled pressure, thus opening the way to gas hydrate studies. In the absence of dissolved gas, i.e., at ambient pressure, we observe ice nucleation to be weakly promoted by titanium oxide and montmorillonite particles, and strongly promoted by silver iodide, in agreement with literature results. Ice nucleation is also promoted when the carrier oil is more wetting towards the capillary, which is the case for fluorinated oil as compared to n-hexane. With cyclopentane, a hydrate-former, as the carrier oil, and dissolved CO2, also a hydrate-former and a "help gas" for cyclopentane hydrate formation, we find evidence for hydrate nucleation along with that of ice, and monitor the different solid phases as temperature varies. (C) 2018 Published by Elsevier Ltd.

To better understand the water-in-oil (w/o) emulsion stability problem, the interfacial material (IM) of four different crude oils was isolated using the wet silica method and analyzed by different techniques. In part 1 (10.1021/acs.energyfuels.6b02899), we used gel permeation chromatography to analyze the molecular size distribution of S-, Ni-, and V-containing compounds. Here, we report the use of dilatational and shear interfacial rheology to analyze the interfacial properties of the IM films. In the second part of this series of papers, it is shown that the wet silica isolation method is reproducible and concentrates the most surface-active molecules present in crude oils. Shear interfacial rheology results showed perfect correlation to emulsion stability; stronger mechanical properties lead to more stable w/o emulsions. Dilatational rheology revealed that successive IM extracts from a crude oil are composed of molecules that behave increasingly like insoluble surfactants that aggregate at the w/o interface. Lastly, shear rheology experiments with diluted IM and diluted crude oil showed some differences that were ascribed to a different partitioning between the bulk and interface.

Round glass capillaries are a basic tool in soft-matter science, but often are shunned due to the astigmatism they introduce in micrographs. Here, we show how refraction in a capillary can be a help instead of a hindrance to obtain precise and sensitive information on two important interfacial properties: the contact angle of two immiscible fluids and the presence of thin films on the capillary wall. Understanding optical cusps due to refraction allows direct mesurement of the inner diameter of a capillary at the meniscus, which, with the height of the meniscus cap, determines the contact angle. The meniscus can thus be measured without intrusive additives to enhance visibility, such as dyes or calibrated particles, in uniform, curved, or even tapered capillaries or under demanding conditions not accessible by conventional methods, such as small volumes (μL), high temperatures, or high pressures. We further elicit the conditions for strong internal reflection on the inner capillary wall, involving the wall and fluid refractive indices and the wall thickness, and show how to choose the capillary section to detect thin (submicron) layers on the wall, by the contribution of total internal reflection to the cusps. As examples, we report the following: (i) CO2-water or -brine contact angles at glass interfaces, measured at temperatures and pressures up to 200 °C and 600 bar, revealing an effect apparently so far unreported-the decrease in the water-wet character of glass, due to dissolved salts in brine, is strongly reduced at high temperatures, where contact angles converge toward the values in pure water; (ii) A tenuous gas hydrate layer growing from the water-guest contact line on glass, invisible in transmission microscopy but prominent in the cusps due to total internal reflection.

The interfacial material (IM) from four different crude oils with different capabilities to form stable water-in-oil (w/o) emulsion was extracted with the wet silica method and analyzed by different techniques. In the first of a series of papers, we report the use of gel permeation chromatography inductively coupled plasma high-resolution mass spectrometry (GPC ICP HR MS) to analyze the size distributions of sulfur-, vanadium-, and nickel-containing compounds present in the IM. The analysis of replicate samples demonstrated the reproducibility of the wet silica extraction method, and successive extractions of the same crude oil concentrated larger and more insoluble IM aggregates containing S, V, and Ni. The analysis of the IM from different crude oils revealed that there is a similar, selective adsorption of high-molecular-weight compounds containing Ni and V at the w/o interface. Conversely, the sulfur profiles for all of these IMs were unique, and given their widely varying ability to stabilize emulsions, it suggests that these species may play a role in the stability of water-in-crude oil emulsions.

Chapter 3 High-Resolution Optical Microscopy of Gas Hydrates Nelly Hobeika, Nelly HobeikaSearch for more papers by this authorMaria Lourdes Martinez De Baños, Maria Lourdes Martinez De BañosSearch for more papers by this authorPatrick Bouriat, Patrick BouriatSearch for more papers by this authorDaniel Broseta, Daniel BrosetaSearch for more papers by this authorRoss Brown, Ross BrownSearch for more papers by this author Nelly Hobeika, Nelly HobeikaSearch for more papers by this authorMaria Lourdes Martinez De Baños, Maria Lourdes Martinez De BañosSearch for more papers by this authorPatrick Bouriat, Patrick BouriatSearch for more papers by this authorDaniel Broseta, Daniel BrosetaSearch for more papers by this authorRoss Brown, Ross BrownSearch for more papers by this author Book Editor(s):Daniel Broseta, Daniel BrosetaSearch for more papers by this authorLivio Ruffine, Livio RuffineSearch for more papers by this authorArnaud Desmedt, Arnaud DesmedtSearch for more papers by this author First published: 30 June 2017 https://doi.org/10.1002/9781119332688.ch3Citations: 3 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter reviews high-resolution optical microscopy methods and highlights their value for gas hydrate research with examples addressing a model hydrate system, cyclopentane hydrate. It illustrates the potential and complementarity of various imaging modes including differential interference contrast (DIC), dark field, fluorescence and (confocal) reflection. These modes are readily available in modern, infinity-corrected optical microscopes. The chapter also illustrates the potential of Brewster angle microscopy for precise imaging of lateral heterogeneities on a planar surface. Based on Brewster angle microscopy observations, the chapter argues that nonuniform (or "patchy") polymer adsorption is responsible for these two apparently contradictory phenomena — inhibition of gas hydrate formation and enhanced stability of the formed hydrate. The proposed mechanism is similar to that proposed in the literature for explaining both why anti-freeze proteins (AFPs) stop ice growth at T well below 0 °C and why ice crystals melt at temperatures significantly above 0 °C up to ~0.5 °C. Citing Literature Gas Hydrates 1: Fundamentals, Characterization and Modeling RelatedInformation

Growth of gas hydrates as fast-growing polycrystalline crusts at interfaces between water and guest phases is well documented, but the mechanisms of hydrate growth on solid substrates are much less known. We report here on cyclopentane (CP) hydrate spreading on glass (fused silica) under CP. As seen for methane hydrate by Beltran and Servio (Cryst. Growth Des. 2010, 10, 4339-4347), CP hydrate grows on glass as a "halo" radiating from the contact line of a primary drop. Complementary optical microscopies at micron resolution here allow identification of the mechanisms of halo growth and melting. We conclude that forms of water on the substrate control halo spreading, namely, a precursor film near the contact line and a breath figure (dew) condensed from the CP (halo spreading at <= 2 mu m s(-1) at T approximate to 0 degrees C or subcooling similar to 7 degrees C), and "leap-frogging" (at similar to 10 mu m s(-1)) over secondary drops left behind by melting a previous halo. Halo thickening, about 5 nm s(-1), is attributed to water condensation, either incorporation of water dissolved in CP (like ablimation) or settling of water "fog" from the CP. Halos spread slower on untreated, compared to hydrophilic, glass, an effect attributed to the quantity of water present on the substrate; a similar trend is noted when the CP phase is not pre-equilibrated with water prior to the experiment. No hydrate halo was detected on hydrophobized (silane-treated) glass, where the breath figure is absent.

A simple millifluidic method is used for studying hydrate crystallization. Regularly-spaced water drops of equal volume in the µl range separated by the guest (hydrate-former) phase are placed in transparent plastic tubing. Temperature and/or pressure are controlled. In one experiment several tens of water drops behaving as independent reactors are video-monitored for hydrate formation and melting events. This method is used here to gain insights into the ‘memory effect’. The hydrate-former chosen is cyclopentane (CP), which forms hydrates at ambient pressure and temperatures below Teq=7.2°C, the three-phase (CP, water, hydrate) equilibrium temperature. The statistics of hydrate nucleation events when chilling the water drops below Teq is observed to depend strongly on the thermal history, e.g., prior CP hydrate formation and subsequent melting at various prescribed temperatures (above 7.2°C) and durations. When one or two of these parameters (melting temperature and duration) increase, the ‘memory’ of the hydrate previously formed fades: the subcoolings required for hydrate formation increase and are more scattered, i.e., they differ more from one drop to the other. The method also allows the visualization of single-drop events such as hydrate birth and growth. The results complement those obtained from more conventional methods and show the promises of using this method for investigating the kinetics of hydrate crystallization and melting.