Bulk Liquid Phase Research Articles

Investigation of gas hydrate formation and inhibition in oil-water system containing model asphaltene

Gas hydrate and asphaltene are two major flow assurance issues that will cause severe plugging in the subsea transportation pipelines, but the detailed understanding of their interactions remains insufficient. Systematic experiments were performed in the present study to investigate the influence of light oil components and asphaltene on gas hydrate formation, and to evaluate the performance of commercial kinetic hydrate inhibitors (KHIs) in different oil-water systems. Results demonstrated the promotion effect of light oil on initial hydrate growth, and the inhibition effect of asphaltene particularly with the light oil solvent of toluene. The influence mechanisms of asphaltene were based on the weakening mass transfer of methane at the gas-liquid interface, and the adsorption of free methane in the bulk liquid phase, while the degree of inhibition on hydrate formation was not positively related to the total concentration of asphaltene. Results also indicated that light oil components can weaken the performance of KHIs, but the role of asphaltene was closed related to the type of KHIs and light oil solvent. The overall experimental results of gas hydrate formation in the asphaltene system are consistent with our previous molecular dynamics simulations researches. Meanwhile, it provides an implication that asphaltene may have a potential ability to help some KHIs recover their inhibition performance, and emphasizes the necessity in systematically considering the oil composition when attempting to develop and utilize KHIs in oil-water system.

Selective adsorption of acidic gases from ternary mixture by acetate- and sulfonate-based ionic liquids at molecular level.

This paper attempts to elucidate the competitive adsorption mechanism of thin films of ionic liquids (ILs) on the surface of porous materials for acidic gases at a molecular level in order to design a proper material for the diminishment of gas emissions. Thin film 1-butyl-3-methylimidazalium ([BMIM]+) cation-based IL systems composed of four different anions such as [CH3CO2]- and [CF3CO2]- (acetate-based), and [CH3SO3]- and [CF3SO3]- (sulfonate-based) are created in contact with the gas phase containing ternary H2S/CO2/CH4:1/25/74 mixture. To define gas adsorption performance at gas-liquid interface and bulk liquid phase, classical molecular dynamics simulations are carried out. Adsorption of acidic gases is governed by the formation of an adsorbed gas layer on the surface of the ionic liquid based on thermodynamics aspects, and then the partial dissolution of gases in the bulk liquid phase is accompanied by the transport of gases. These behaviors are followed by several analysis methods in simulation approaches such as radial distribution function (RDF) of gases around specific atoms of ILs, lateral displacement of gas molecules, radial distance between gas and ILs, interaction energy between gases and ILs, and average number of hydrogen bonding between ions with and without adsorbed gases. Acetate-based ILs performed twice as good in CO2 adsorption capacity than sulfonate-based ILs. However, the one having -CF3 group in acetate-based ILs has short CO2 retention time and high CH4 adsorption capacity, diminishing the H2S+CO2/CH4 adsorption selectivity. High CO2 adsorption performance of acetate-based ILs is related to their strong anion-cation interaction and less hydrogen-bonding ability between cation tail and anion, which is the source for free space between anion and cation. Those with high adsorption capacities and long retention times are those that can ensure that CO2 molecules are coordinated in these free volumes between cation tails and anions. Therefore, here, the effect of different parameters on the CO2 and H2S adsorption over CH4 is revealed via atomistic design, and the importance of selection of suitable anions in IL for identifying potential nanocomposite adsorbent materials for acidic gas removal is highlighted.

Sustainable existence of solid mercury (Hg) nanoparticles at room temperature and their applications.

Although liquid mercury (Hg) has been known since antiquity, the formation of stable solid nano forms of Hg at room temperature has not been reported so far. Here, for the first time, we report a simple sonochemical route to obtain solid mercury nanoparticles, stabilized by reduced graphene oxide at ambient conditions. The as-formed solid Hg nanoparticles were found to exhibit remarkable rhombohedral morphology and crystallinity at room temperature. Extensive characterization using various physicochemical techniques revealed the unique properties of the solid nanoparticles of Hg compared to its bulk liquid metal phase. Furthermore, the solid nature of the Hg nanoparticles was studied electrochemically, revealing distinctive properties. We believe that solid Hg nanoparticles have the potential for important applications in the fields of electroanalytical chemistry and electrocatalysis.

First hyperpolarizability of water at the air-vapor interface: a QM/MM study questions standard experimental approximations.

Surface Second-Harmonic Generation (S-SHG) experiments provide a unique approach to probe interfaces. One important issue for S-SHG is how to interpret the S-SHG intensities at the molecular level. Established frameworks commonly assume that each molecule emits light according to an average molecular hyperpolarizability tensor β(-2ω,ω,ω). However, for water molecules, this first hyperpolarizability is known to be extremely sensitive to their environment. We have investigated the molecular first hyperpolarizability of water molecules within the liquid-vapor interface, using a quantum description with explicit, inhomogeneous electrostatic embedding. The resulting average molecular first hyperpolarizability tensor depends on the distance relative to the interface, and it practically respects the Kleinman symmetry everywhere in the liquid. Within this numerical approach, based on the dipolar approximation, the water layer contributing to the Surface Second Harmonic Generation (S-SHG) intensity is less than a nanometer. The results reported here question standard interpretations based on a single, averaged hyperpolarizability for all molecules at the interface. Not only the molecular first hyperpolarizability tensor significantly depends on the distance relative to the interface, but it is also correlated to the molecular orientation. Such hyperpolarizability fluctuations may impact the S-SHG intensity emitted by an aqueous interface.

Experimental Evidence of Gas Hydrates Dissociation Kinetics by Shifting their Equilibrium Conditions

The scope of this study is to define the rates under which multi-component gas hydrates contained in the pore space of a mud volcanos’ (MV) sediments may decompose in gas and water phase as a result of pressure decrease or temperature increase. Such cases can be encountered during retrieval and handling of pristine samples from the sea floor, or due to an increase of hot mud fluxes from underneath the MV area. Both of the aforementioned shifts of conditions have been studied in the bulk liquid phase of a reactor, while pressure decrease has also been studied in a piston vessel containing artificial sediment at the Centre for Gas Hydrates Research, HW University, Edinburgh.The results indicate that gas hydrate dissociation progresses much faster with pressure decrease than with temperature increase. Moreover, depressurization at temperatures above 15°C causes higher dissociation rates in comparison to that at lower temperatures.

Strong Activity Enhancement of the Photocatalytic Degradation of an Azo Dye on Au/TiO2 Doped with FeOx

The doping of Au/TiO2 with FeOx is shown to result in a strong enhancement of its photocatalytic activity in the degradation of the azo dye Orange II. In order to examine the source of this enhancement, Au-FeOx/TiO2 nanocomposites containing different molar ratios of Au:Fe were synthesized, and X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and high-resolution transmission electron microscope (HRTEM) analyses indicated that the TiO2-supported Au nanoparticles were partially covered with an amorphous layer of FeOx species, in which the iron was present as Fe2+ and Fe3+. The metal-semiconductor system, i.e., Au/TiO2, showed only a moderate degradation rate, whereas doping with FeOx strongly enhanced the degradation activity. The bandgap energy decreased gradually from Au/TiO2 (3.13 eV) to the catalyst with the highest FeOx loading Au-FeOx (1:2)/TiO2 (2.23 eV), and this decrease was accompanied by a steady increase in the degradation activity of the catalysts. XPS analyses revealed that compared to Au/TiO2, on Au-FeOx/TiO2 a much higher population density of chemisorbed and/or dissociated oxygen species was generated, which together with the decreased bandgap resulted in the highest photocatalytic activity observed with Au-FeOx (1:2)/TiO2. The processes occurring during reaction on the catalyst surface and in the bulk liquid phase were investigated using operando attenuated total reflection IR spectroscopy (ATR-IR) combined with modulation excitation spectroscopy (MES), which showed that the doping of Au/TiO2 with FeOx weakens the interaction of the dye with the catalyst surface and strongly enhances the cleavage of the azo bond.

Thermodynamic Stability of Volatile Droplets and Thin Films Governed by Disjoining Pressure in Open and Closed Containers.

Distributed thin films of water and their coexistence with droplets are investigated using a capillary description based on a thermodynamic fundamental relation for the film Helmholtz energy, derived from disjoining pressure isotherms and an accurate equation of state. Gas–film and film–solid interfacial tensions are derived, and the latter has a dependence on film thickness. The resulting energy functionals from the capillary description are discretized, and stationary states are identified. The thermodynamic stability of configurations with thin films in systems that are closed (canonical ensemble) or connected to a particle reservoir (grand canonical ensemble) is evaluated by considering the eigenvalues of the corresponding Hessian matrices. The conventional stability criterion from the literature states that thin flat films are stable when the derivative of the disjoining pressure with respect to the film thickness is negative. This criterion is found to apply only in open systems. A closer inspection of the eigenvectors of the negative eigenvalues shows that condensation/evaporation destabilizes the film in an open system. In closed systems, thin films can be stable even though the disjoining pressure derivative is positive, and their stability is governed by mechanical instabilities of a similar kind to those responsible for spinodal dewetting in nonvolatile systems. The films are stabilized when their thickness and disjoining pressure derivative are such that the minimum unstable wavelength is larger than the container diameter. Droplets in coexistence with thin films are found to be unstable for all considered examples in open systems. In closed systems, they are found to be stable under certain conditions. The unstable droplets in both open and closed systems are saddle points in their respective energy landscapes. In the closed system, they represent the activation barrier for the transition between a stable film and a stable droplet. In the open system, the unstable droplets represent the activation barrier for the transition from a film into a bulk liquid phase. Thin films are found to be the equilibrium configuration up to a certain value of the total density in a closed system. Beyond this value, there is a morphological phase transition to stable droplet configurations.

Densification and tribofilm formation in hydrocarbon nanofluids induced by MoS2 nanotubes

The nanoscopic behaviour of dispersions of MoS2 nanotubes in hydrocarbons was studied by molecular dynamics simulations. The reported results allowed the analysis of hydrocarbons adsorption at nanotubes external wall as well as the behaviour of the confined phase of hydrocarbons inside the nanotubes internal cavity. The adsorption and confinement of hydrocarbons leads to large structural rearrangements in the vicinity of the nanotubes in comparison with bulk liquid phase, which are pivotal for the behaviour of these nanofluids as lubricant media. The large affinity of the considered hydrocarbons for the nanotubes surfaces and cavities determines the stability of the considered dispersions and it allows the application of these nanofluids for several technologies in particular for enhanced lubrication.

Kinetic study of fuel bio-additive synthesis from glycerol esterification with acetic acid over acid polymeric resin as catalyst

The increase of remnant of glycerol from biodiesel production results in the need to develop valorization strategies for this low-cost by-product. In this context, bio-additives synthesis from glycerol such as acetylglycerides has emerged as an economically viable alternative. In this work, a kinetic study of glycerol esterification with acetic acid over Dowex 650C ion exchange resin as catalyst to obtain fuel bio-additives was performed. The experimental study was carried out in a batch reactor at 353–393 K temperature range using acetic acid to glycerol molar ratio from 3:1 to 9:1 and catalyst loading between 4 and 8 wt%.Furthermore, different kinetic models based on the Langmuir-Hinshelwood-Hougen-Watson (LHHW), Eley-Rideal (ER) and Power Law (PL) approaches were proposed in order to correlate the experimental data. In addition, it was determined that the intraparticle and extraparticle mass and heat transfer resistances in the polymeric resin are negligible. The obtained results from kinetics modeling evidence that the best model to describe the studied reaction was the Eley-Rideal. In this model, it was considered that the catalytic surface reaction was the controlling reaction stage, which involves the reaction between adsorbed acetic acid and glycerol as well as mono- and diglycerides from the bulk liquid phase, generating the corresponding acylglycerides and water. Moreover, it was found that glycerol and water adsorption on the catalytic surface is stronger than that for acetic acid and acetylglycerides.

Prediction of the solid-liquid interface energy of a multicomponent metallic alloy via a solid-liquid interface sublattice model

Despite central roles in solidification and crystal growth, the solid-liquid interface energy σsl of the multicomponent metallic alloys is scarce and scattered because of the experimental complexity in measurements. Moreover, the theoretical prediction of σsl of the metallic alloy has been long suffered from the incomplete understanding of the solid-liquid interface structures. In this paper, the solid-liquid interface of the metallic alloy is reduced to a two-dimensional layer composed of the solid sublattice and liquid sublattice that is further sandwiched by the bulk solid and liquid phases. This enables the well-defined enthalpy and entropy hence the Gibbs energy model of the metallic solid-liquid interface layer. Via a constraint minimization of the solid-liquid interface layer Gibbs energy, the composition- and temperature-dependent σsl of the Al-based and Ag-based alloys are calculated by coupling with the available thermodynamic model parameters of the alloys. The calculation results are validated by the experimental data. It demonstrates that the built interface sublattice model offers a self-consistent framework for the automatic prediction of σsl of the metallic alloys ranging from the binary to a multicomponent system. It thus provides a more compelling solution to the long-standing issue associated with the modeling of the solid-liquid interface thermodynamics of the metallic alloys under both undercooling and equilibrium states.

Bubble Formation in a Finite Cone: More Pieces to the Puzzle.

We investigate the stability of bubble formation, starting with a convex or a concave meniscus, from a liquid solution (of water and a dissolved gas) inside a finite cone at constant temperature and constant liquid pressure (above the saturation pressure of the pure solvent). It is assumed that the dissolved gas (nitrogen) forms a dilute solution at equilibrium, which can be described by Henry's law. The number and nature of equilibrium states are determined with Gibbsian composite-system thermodynamics, both from the intersection of the equilibrium Kelvin radius with the geometry radius and from the extrema in the plot of free energy of the system versus size of the new phase. Bubble stability is studied along the whole growth path, as the bubble grows inside, gets pinned, and grows further outside the finite cone. The changes in the concentration of the liquid bulk phase and the vapor phase during the growth of the bubble are carefully incorporated in the equations. The effects of various parameters, including cone apex angle, cone half mouth radius, contact angle, total number of moles, and initial degree of saturation, on the stability of the bubble are also investigated. Stability of bubble formation from a liquid solution inside a confined geometry such as a finite cone is of interest in areas such as restoring underwater superhydrophobicity and adhesion of particles to the roughness of synthetic biomaterials.

Risk Assessment for Metalworking Fluids and Respiratory Outcomes.

BackgroundMetalworking fluids (MWFs) are mixtures with inhalation exposures as mists, dusts, and vapors, and dermal exposure in the dispersed and bulk liquid phase. A quantitative risk assessment was performed for exposure to MWF and respiratory disease.MethodsRisks associated with MWF were derived from published studies and NIOSH Health Hazard Evaluations, and lifetime risks were calculated. The outcomes analyzed included adult onset asthma, hypersensitivity pneumonitis, pulmonary function impairment, and reported symptoms. Incidence rates were compiled or estimated, and annual proportional loss of respiratory capacity was derived from cross-sectional assessments.ResultsA strong healthy worker survivor effect was present. New-onset asthma and hypersensitivity pneumonitis, at 0.1 mg/m3 MWF under continuous outbreak conditions, had a lifetime risk of 45%; if the associated microbiological conditions occur with only 5% prevalence, then the lifetime risk would be about 3%. At 0.1 mg/m3, the estimate of excess lifetime risk of attributable pulmonary impairment was 0.25%, which may have been underestimated by a factor of 5 or more by a strong healthy worker survivor effect. The symptom prevalence associated with respiratory impairment at 0.1 mg/m3 MWF was estimated to be 5% (published studies) and 21% (Health Hazard Evaluations).ConclusionSignificant risks of impairment and chronic disease occurred at 0.1 mg/m3 for MWFs in use mostly before 2000. Evolving MWFs contain new ingredients with uncharacterized long-term hazards.

Vertical Distribution of Brine and Volume Structure of Thin Annual Ice in Amursky Bay Based on the Methods of Nuclear Magnetic Resonance and Magnetic Resonance Imaging

Spatial distribution of the liquid and solid phases in the pores of first-year sea ice in Amursky Bay was studied using the method of nuclear magnetic resonance and magnetic resonance imaging in the period from 2013 to 2016. We describe the influence of snow cover on the brine content in the pores of sea ice, on the bulk structure of crystalline formations, and on the formation of its individual layers. The difference in vertical profiles of temperature and salinity in the winter and spring periods is shown. The characteristic features of the bulk crystal structure and liquid phase in thin first-year ice are compared with the thick ice of the polar regions. A new empirical relationship is given for the calculation of the entire thickness and separate ice layers as applied to thin young ice.

Microelectrode Based Devices for Diagnosis of Electron Transport and Electrochemical Behavior of Redox-Conducting Materials

We are going to address practical issues related to the principles and analytical aspects of electrochemical studies (typically done at room temperature) of solid, rigid or semi-rigid (nonfluid) systems in the absence of a liquid solution phase. Representative examples include redox and conducting organic polymers, melts and solid solutions of redox centers in solid ionic conductors, mixed-valence polynuclear inorganic materials, transition metal salts, oxides, and zeolites. The emphasis is on the elements of dynamics for the efficient delivery of charge and on reactivity of the ‘redox conducting’ materials. The effective (apparent) diffusional mechanism is critical to the success of most analytical measurements in solid-state. Historically, electrochemistry in the absence of a bulk liquid phase has focused on the problems of energy storage and production. Recently, it has become possible to apply conventional electrochemical methods to characterize solid-state type redox electrolytes with respect to analytical characterization of materials, measurement of electron transfer rates, and determination of analytes using amperometric sensing. The characterization of materials by solid-state voltammetry primarily has focused on mixed-valence, ionically conducting compounds and on diverse organic ionomers hosting identifiable molecular (redox) sites. Potential materials for solid-state electrochemical measurements are expected to contain three-dimensionally distributed highly concentrated redox centers between which fast electron self-exchange (hopping) is feasible. Among inorganic systems, single crystals of heteropolyacids of molybdenum and tungsten, as well thin films of Prussian Blue type metal hexacyanoferrates will be considered. These redox centers are fixed and, although they may have short range mobility about an equilibrium position, they classically are macroscopically immobile. The applicable materials also must host mobile counter-ions that are capable of providing charge balance during electron transfers, thereby serving the same purpose as the supporting electrolytes in conventional electrochemistry. The population of these ions must be sufficient to support diffusive mass transport of electrons and to minimize ohmic effects. We will describe typical electrochemical cells and experimental tactics to overcome the relatively slow dynamics of transport in solid (non-fluid) systems. Application of microdimensional electrodes leads to an improvement in the quality of solid-state electrochemical data and provides new diagnostic and analytical possibilities. Basic concepts of mechanistic studies, which are relevant to the development of novel analytical methods, together with trends towards possible future applications will also be addressed.

OH radical in water from ab initio molecular dynamics simulation employing hybrid functionals

This work presents for the first time ab initio molecular dynamics simulations for the OH⋆-(H2O)n cluster with n = 0–5 and the OH radical in the bulk phase, using B3LYP as a functional. Furthermore, for OH⋆-w31, simulations with PBE0 and HSE03 are also investigated. In all systems, the OH radical is a stronger hydrogen bond donor than acceptor; a stronger hydrogen bond donor than water and a weaker hydrogen bond acceptor than water. Radial distribution functions (RDFs) reveal that for all systems, neither a hemibond between radical and water nor hydrogen abstraction is present. Comparisons with past simulations indicate that BLYP leads to artifacts, such as overstructuring of water in OH⋆-w31 and the hemibonded structure. In order to have strong hydrogen bonds with an extensive hydrogen bond network, at least four water molecules are necessary. RDFs as well as continuous dimer existence autocorrelation functions show that the OH radical is not disrupting the hydrogen bond network of water. In the bulk phase, the acceptor interaction is a very low probable interaction, whereas in the gas phase, it has a higher probability. The orientation of the water molecule around the OH radical is in the bulk liquid phase much less and in the gas phase enhanced, especially for the OH radical acting as a hydrogen bond donor toward one water molecule. PBE0 results for OH⋆-w31 in a strong hydrogen bond donor interaction compared to HSE03 and B3LYP, which has the weakest interaction. HSE03 leads to strong O–H interactions in OH⋆-w31, followed by PBE0 and B3LYP.

Design of a biodegradable carrier for the application of controller bacteria on air–water interfaces

The formulation of a biodegradable carrier which effectively concentrates microorganisms on air-water interfaces is proposed. This avoids the dispersion of bacteria into the bulk liquid phase and at the same time prevents their sedimentation. This formulation can be used in biocontrol and bioremediation treatments where the target is at the position of the air-water interface, as in the case of the treatment of rice diseases caused by Sclerotium oryzae and Rhizoctonia complex. The carrier is an oil-in-water (O/W) emulsion which contains lecithin and chitosan in both phases at different proportions. In a stable formulation, bacteria that are adsorbed onto the surface of oil droplets are carried with them and flowed upward to the air-water interface, due to buoyancy forces. When using the biodegradable carrier, it is possible to recover at least 15-fold more bacteria from the air-water interface than in the case of using the aqueous formulation. The emulsion O/W is applied to the surface by dripping, resulting in a homogeneous two-dimensional film distribution. With this application device, the number of bacteria at the air-water interface is significantly increased. © 2019 Society of Chemical Industry.

Bioelectrochemical Nitrogen Fixation (e-BNF) Towards the Electrosynthesis of Biomass

The industrial synthesis (Haber-Bosch process) of mineral-N has been showing its dark side. Facing the enormous challenge of feeding humankind new technological solutions should enable sustainable nitrogen (N) fixation, to preserve soil fertility. We introduce a new type of microbial electrosynthesis, aimed at simultaneously fixing N2 and inorganic carbon. In this new perspective, the aim is enhancing biological nitrogen fixation by electrostimulation of complex microbial communities, to produce whole biomass, which can be used as soil fertilizer. Two preliminary contributions in this field reported: a) a bioelectrochemical version of the Haber-bosh process, where methyl viologen shuttled electrons to purified nitrogenase enzymes (Milton et al., 2017) and b) the stimulation of N-fixation in a pure planktonic culture of X. autotrophicus by H2-evolution with a specific abiotic catalyst (Liu et al., 2017). Here, a cathodic biofilm was enriched in electro-active autotrophic nitrogen fixers, starting from a mixed microbial culture. The cathode, a carbon-fibers conductor, was kept under constant polarization (-0.7 V vs SHE). Biomass (in the biofilm, as well as in the bulk liquid phase) was synthesized at significantly higher rates (up to 18-fold), as compared to controls kept at open circuit (OC). Along over 100 days, electron transfer had increased by 30-fold, as compared to abiotic conditions. Metagenomics evidenced Nif genes associated to autotrophs (both Archaea and Bacteria) only in polarized biofilms, while not in OC control. Genes copies encoding for a series of known proteins associated to extracellular electron transfer were double in polarized trials, as compared to controls. The first results of such an approach were recently published in Bioelectrochemistry (Rago et al., 2019). From this proof-of-the-concept, we propose to call this promising field ‘bio-electrochemical nitrogen fixation (e-BNF)’, that deserve future research efforts in both fundamentals and applicative aspects. Liu, C., Sakimoto, K.K., Colón, B.C., Silver, P.A., Nocera, D.G., 2017. Ambient nitrogen reduction cycle using a hybrid inorganic–biological system. Proc. Natl. Acad. Sci. 114, 6450–6455. doi:10.1073/pnas.1706371114 Milton, R.D., Cai, R., Abdellaoui, S., Leech, D., De Lacey, A.L., Pita, M., Minteer, S.D., 2017. Bioelectrochemical Haber–Bosch Process: An Ammonia-Producing H2/N2Fuel Cell. Angew. Chemie - Int. Ed. 56, 2680–2683. doi:10.1002/anie.201612500 Rago, L., Zecchin, S., Villa, F., Goglio, A., Corsini, A., Cavalca, L. & Schievano, A. 2019, ‘Bioelectrochemical Nitrogen fixation (e-BNF): Electro-stimulation of enriched biofilm communities drives autotrophic nitrogen and carbon fixation’, Bioelectrochemistry, vol. 125, pp. 105–15. Figure 1

Investigation of the liquid-vapour interface of aqueous methylamine solutions by computer simulation methods

Molecular dynamics simulations of the liquid-vapour interface of water-methylamine mixtures of eight different compositions, including neat water, are performed on the canonical (N,V,T) ensemble at 280 K. The molecules constituting the first three individual molecular layers beneath the liquid surface are identified by the Identification of the Truly Interfacial Molecules (ITIM) method. The results indicate that methylamine molecules are strongly adsorbed in the first, and somewhat depleted in the second molecular layer, while the composition of the third layer agrees well with that of the bulk liquid phase. On the other hand, methylamine molecules do not show considerable self-association within the surface layer. The orientational preferences of the methylamine molecules at the liquid surface are clearly governed by the requirement of maximizing their hydrogen bonding interaction. As a consequence, methylamine molecules point by their apolar CH3 group straight to the vapour, while by the potential hydrogen bonding directions of the NH2 group flatly to the liquid phase. Further, within the surface layer, methylamine molecules stay, on average, noticeably farther from the bulk liquid phase than waters. Increasing methylamine mole fraction leads to the gradual breaking up of the lateral percolating H-bonding network of the surface molecules. Finally, methylamine molecules accelerate, while water molecules slow down the exchange of both species between the liquid surface and the bulk liquid phase. Further, methylamine molecules slow down the lateral diffusion of each other, and even prevent water molecules from showing noticeable lateral diffusion within the surface layer. The reason for this latter effect is that the mean residence time of the water molecules at the liquid surface becomes considerably shorter than the characteristic time of their lateral diffusion in the presence of methylamine.

Spontaneous nano-emulsification with tailor-made amphiphilic polymers and related monomers

In general, nano-emulsions are submicron droplets composed of liquid oil phase dispersed in liquid aqueous bulk phase. They are stable and very powerful systems when it regards the encapsulation of lipophilic compounds and their dispersion in aqueous medium. On the other hand, when the properties of the nano-emulsions aim to be modified, e.g. for changing their surface properties, decorating the droplets with targeting ligands, or modifying the surface charge, the dynamic liquid / liquid interfaces make it relatively challenging. In this study, we have explored the development of nano-emulsions which were not anymore stabilized with a classical low-molecular weight surfactant, but instead, with an amphiphilic polymer based on poly(maleic anhydride-alt-1-octadecene) (PMAO) and Jeffamine®, a hydrophilic amino-terminated PPG/PEG copolymer. Using a polymer as stabilizer is a potential solution for the nano-emulsion functionalization, ensuring the droplet stabilization as well as being a platform for the droplet decoration with ligands (for instance after addition of function groups in the terminations of the chains). The main idea of the present work was to understand if the spontaneous emulsification –commonly performed with nonionic surfactants– can be transposed with amphiphilic polymers, and a secondary objective was to identify the main parameters impacting on the process. PMAO was modified with two different Jeffamine®, additionally different oils and different formulation conditions were evaluated. As a control, the parent monomer, octadecyl succinic anhydride (OSA) was also modified and studied in the similar way as that of polymer. The generated nano-emulsions were mainly studied by dynamic light scattering and electron microscopy, that allows discriminating the crucial parameters in the spontaneous process, originally conducted with polymers as only stabilizer.

Comparative study of directional solidification of Al-7 wt% Si alloys in Space and on Earth: Effects of gravity on dendrite growth and Columnar-to-equiaxed transition

Directional solidification experiments of grain refined Al −7 wt% Si alloy were carried out on Earth under normal gravity conditions (1 g) and in the Material Science Laboratory on board the International Space Station in microgravity environment (µg), to investigate the impact of the gravity on the solidification microstructure and the columnar-to-equiaxed transition (CET). The increase of the dendrite growth velocity imposed by the processing conditions during the experiments leads to a size decrease of the dendrite microstructure and to a more homogeneous eutectic distribution under both 1 g and μg conditions. A progressive CET is obtained in both samples implying the existence of an intermediate region after the inception position of CET defined as the end of growth of the columnar dendrites. However, a more progressive CET and longer dendrites aligned with the applied temperature gradient are observed in presence of gravity. This difference is attributed to the convective flow on Earth. On the one hand, it carries the grains that nucleate ahead of the columnar front away into the bulk liquid phase. On the other hand, it sweeps the solute away from the dendrite tip zone. Consequently, the blocking effect is diminished, allowing extended continuous growth of the elongated dendrites.