Stability studies of high-stable water-in-oil model emulsions

Different compositions and emulsification protocols were used to prepare stable water-in-oil (w/o) emulsions. Water, mineral oil, and a mixture of Span 80 and Tween 80 surfactants were combined to form emulsions that can be used as reference for electrolyte-free systems. Here, we have proposed emulsions wherein different properties were evaluated. Electrical conductivity measurements indicated that conductivity increases linearly with increasing surfactant content. The emulsions’ flow curves and viscoelastic behaviors were delineated by rheological measurements. Stability studies by centrifugal testing have shown that smaller the surfactant content, lower the stability, for any used stirring speeds. Furthermore, higher the applied mixing rate to make the emulsion, higher the stability, regardless of the amount of surfactant. Electrical field stability analysis showed, for all systems, that critical electric field (CEF) values were dependent on either surfactant amount and emulsion elastic modulus.     

High precision X-ray diffraction studies of polycrystalline materials on synchrotron radiation

The review is devoted to application of synchrotron radiation (SR) for studying the structure of polycrystalline materials. The main emphasis is made on the equipment and techniques for acquiring high precision structural information — high angular resolution powder diffractometry and the use of anomalous scattering effect in structural studies. Various schemes of recording the high resolution X-ray patterns are presented, diffractometers operating in the world’s leading synchrotron radiation centers are described, and examples of particular applications are reported.     

Synchrotron X-ray diffraction characterization of healthy and fluorotic human dental enamel

With the introduction of fluoride as the main anticaries agent used in preventive dentistry, and perhaps an increase in fluoride in our food chain, dental fluorosis has become an increasing world-wide problem. Visible signs of fluorosis begin to become obvious on the enamel surface as opacities, implying some porosity in the tissue. The mechanisms that conduct the formation of fluorotic enamel are unknown, but should involve modifications in the basic physical-chemistry reactions of demineralization and remineralisation of the enamel of the teeth, which is the same reaction of formation of the enamel's hydroxyapatite (HAp) in the maturation phase. The increase of the amount of fluoride inside of the apatite will result in gradual increase of the lattice parameters. The aim of this work is to characterize the healthy and fluorotic enamel in human tooth using Synchrotron X-ray diffraction. All the scattering profile measurements were carried out at the X-ray diffraction beamline (XRD1) at the Brazilian Synchrotron Light Laboratory—LNLS, Campinas, Brazil. X-ray diffraction experiments were performed both in powder samples and polished surfaces. The powder samples were analyzed to obtain the characterization of a typical healthy enamel pattern. The polished surfaces were analyzed in specific areas that have been identified as fluorotic ones. X-ray diffraction data were obtained for all samples and these data were compared with the control samples and also with the literature data.     

Synchrotron X-ray studies of Ti-doped NaAlH4

Pure and doped NaAlH(4) with 5 mol % Ti on the basis of Ti(13).6THF have been investigated by means of X-ray synchrotron radiation. The Rietveld method has been used to study the possible substitution of Ti inside the NaAlH(4) structure and/or the presence of vacancies. This study indicates that there is no significant variation of the lattice parameter once the Na Alanate is doped with the Ti cluster. From the refinement of the site occupation factors, the substitution of Ti on the Na site can be excluded. A slight improvement was found when Ti was substituted on the Al site, but it is not significant enough to say that Ti definitely substitutes for Al in the Alanate phase. Additionally, there is no evidence for vacancy formation in Ti-colloid-doped sodium Alanate.     

Synchrotron X-ray techniques for the investigation of structures and dynamics in interfacial systems

This review focuses on recent results obtained by synchrotron X-ray techniques applied to the characterization of interfacial systems, with main emphasis on flat interfaces and on colloidal systems. The techniques covered are, for structural determinations: X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and grazing incidence X-ray excited fluorescence (GIXF), while dynamics are investigated by X-ray photon correlation spectroscopy (XPCS) mainly in the grazing-incidence geometry (GIXPCS).The systems reviewed are, in order of growing complexity, floating Langmuir monolayers, supported films of lipids and proteins, polymeric films, buried interfaces, colloidal systems and gels formed by colloids either in 3D or in the form of 2D interfacial layers. Recent results are critically discussed, and some interesting directions of development are outlined, having also in mind new technical developments such as X-ray free electron laser sources and micro-focused synchrotron beamlines.     

Langevin-dynamics simulation of flocculation in water-in-oil emulsions

Aggregation of internal phase droplets in water-in-oil emulsions has been simulated by the Langevin-dynamics method. At initial stages, the process rate obeys the Smoluchowski equations. The concentration ranges have been determined in which percolation clusters are formed. It has been shown that the examined emulsions may be divided into three groups, which enable one to predict their sedimentation stability. Percolation clusters are not formed in emulsions with internal-phase fractions of ≤0.1; therefore, their sedimentation rate is high. In the range of internal-phase fractions from 0.1 to 0.3–0.4, the percolation clusters are formed within a few fractions of a second; however, the rate of subsequent droplet addition to the clusters is low. The flocculation of internal-phase droplets results in the formation of a weak network structure followed by its densification and the separation of a dispersion medium with time. In emulsions with internalphase fractions of >0.3–0.4, almost all droplets unite into percolation clusters within a few fractions of a second. This structure is slowly densified; therefore, the rate of dispersion medium separation is low. The results obtained have been confirmed by experimental data on the sedimentation stability of the water-in-oil emulsions.     

Synchrotron radiation phase-contrast X-ray CT imaging of acupuncture points

Three-dimensional (3D) topographic structures of acupuncture points were investigated by using synchrotron radiation in-line X-ray phase contrast computerized tomography. Two acupuncture points, named Zhongji (RN3) and Zusanli (ST36), were studied. We found an accumulation of microvessels at each acupuncture point region. Images of the tissues surrounding the acupuncture points do not show such kinds of structure. This is the first time that 3D images have revealed the specific structures of acupuncture points.     

Thermal analysis and high-temperature X-ray diffraction of nano-tricalcium phosphate crystallization

Calcium phosphate biomaterials have long ago attracted the interest of world-wide scientists because they form the main inorganic constituent of the human bones and teeth. Classical approaches to synthesize this ceramic material did not give satisfactory results until present, so new approaches are required. In this article the tricalcium phosphate achievement by a method which is a combination of sol–gel and classic precipitation from solution is presented, starting from CaCl₂ as calcium precursor and H₃PO₄ as phosphorus precursor, without pH adjustment. The reaction mixture was allowed to maturate for 2 months, the time influence on the precipitated material being presented in previous articles. Present studies aimed at the influence of temperature on the structural characteristics of precipitated and maturated material, by means of thermal analysis, X-ray diffraction, infrared spectroscopy, and high-temperature X-ray diffraction. A complex type thermal decomposition takes place while heating the sample to 1000 °C, with superposed and parallel processes. The sample goes through alternative amorphous and crystalline stages before final crystallization of β-tricalcium phosphate takes place. The high-temperature XRD studies offered the great advantage of being both a synthesis and a physico-chemical characterization technique, which along with thermal analysis and infrared spectroscopy, gave a lot of useful information in a very short time.     

Comparison of Pickering and network stabilization in water-in-oil emulsions

We compared the efficacy of Pickering crystals, a continuous phase crystal network, and a combination thereof against sedimentation and dispersed phase coalescence in water-in-oil (W/O) emulsions. Using 20 wt % water-in-canola oil emulsions as our model, glycerol monostearate (GMS) permitted Pickering-type stabilization, whereas simultaneous usage of hydrogenated canola oil (HCO) and glycerol monooleate (GMO) primarily led to network-stabilized emulsions. A minimum of 4 wt % GMS or 10 wt % HCO was required for long-term sedimentation stability. Although there were no significant differences between the two in mean droplet size with time, the free water content of the network-stabilized emulsions was higher than Pickering-stabilized emulsions, suggesting higher instability. Microscopy revealed the presence of crystal shells around the dispersed phase in the GMS-stabilized emulsions, whereas in the HCO-stabilized emulsion, spherulitic growth in the continuous phase and on the droplet surface occurred. The displacement energy (E(disp)) to detach crystals from the oil-water interface was ～10(4) kT, and was highest for GMS crystals. Thermal cycling to induce dispersed phase coalescence of the emulsions resulted in desorption of both GMS and GMO from the interface, which we ascribed to solute-solvent hydrogen bonding between the emulsifier molecules and the solvent oil, based on IR spectra. Overall, Pickering crystals were more effective than network crystals for emulsion stabilization. However, the thermal stability of all emulsions was hampered by the diffusion of the molten emulsifiers from the interface.     

Preparation and X-ray diffraction studies of curium hydrides

Curium hydrides were prepared by reaction of curium-248 metal with hydrogen and characterized by X-ray powder diffraction. Several of the syntheses resulted in a hexagonal compound with average lattice parameters of a₀ = 0.3769(8) nm and c₀ = 0.6732(12) nm. These products are considered to be CmH_3?δ by analogy with the behavior of lanthanide-hydrogen and lighter actinide-hydrogen systems. Face-centered cubic products with an average lattice parameter of a₀ = 0.5322(4) nm were obtained from other curium hydride preparations. This parameter is slightly smaller than that reported previously for cubic curium dihydride, CmH_2+x (B. M. Bansal and D. Damien, Inorg. Nucl. Chem. Lett., 6, 603, 1970). The present results established a continuation of typical heavy trivalent lanthanide-like behavior of the transuranium actinide-hydrogen systems through curium.     

Synchrotron radiation diffraction study of structural changes in the interaction of liquid and solid metals

Changes of the structure and phase composition occurring during the interaction of copper and its alloys in the solid-state phase with the liquid melts of indium, gallium and tin are considered. It is shown that the phase and morphological composition of interaction products depends on the relations between the rates of diffusion and the rates of reagent dissolution. Structural transformations that take place during contact melting and eutectic crystallization in the zones of indium–tin and indium–bismuth contacts are also considered. A hypothesis concerning the nature and microstructure of eutectics is proposed. All experiments are performed on the VEPP-3/VEPP-4 storage ring.     

Synchrotron diffraction studies of TiC/FeTi cermets obtained by SHS

TiC/FeTi composites have been obtained in situ by Self-propagating High-temperature Synthesis (SHS) of an intimate mixture of compacted powders of elemental carbon, titanium and iron. The reaction has been followed in real time by X-ray diffraction at the ESRF. The mechanism of the reaction is discussed in terms of the formation of a liquid phase corresponding to the eutectic of the Fe/Ti system prior to the TiC synthesis. Temperatures of reaction have been estimated by correlating thermal expansion coefficients with diffraction peaks shifts. The microstructures obtained by this method, suitable for cutting tools and wear resistant applications, are presented.     

X-ray diffraction studies of mesomorphic ferrocene diesters

Abstract

The crystal and molecular structure of 1,l ′-bis(4′-pentyloxybiphenyl)ferrocene dicarboxylate ester (1) has been determined by X-ray diffraction at 295 and 160K. The molecule is found to exist at both temperatures in an extended S geometry. The carboxyl groups are essentially coplanar with the cyclopentadienyl rings but almost perpendicular to the attached phenyl ring. Low angle X-ray diffraction of three diesters in the smectic phases were also studied. The results were not very definitive because of the lack of thermal stability for the monotropic phase behaviour. Nevertheless, the layer spacing of about 47 A for one of the compounds at 409K is consistent with the extended S shape conformation.     

The use of phase-inverting emulsions to show the phenomenon of interfacial crystallization on both heating and cooling

Highly anomalous crystallization behavior has been achieved in phase-inverting emulsion systems by using nonionic surfactants that induce nucleation. In particular, nucleation can be inhibited at the phase inversion, allowing systems held at, or near, this temperature to undergo crystallization either on heating or cooling. This new phenomenon is demonstrated for 27.4 wt % aqueous glycine solutions emulsified in decane using Span 20 Tween 20 blends. The inhibitory effect on interfacial nucleation at/near the phase inversion is readily shown by the maximum in the induction time for crystallization found in systems at/near the phase-inversion temperature. These findings are unprecedented. An extremely rapid rise in nucleation rate is expected on cooling glycine solutions, owing to the associated increase in supersaturation, the driving force for crystallization. The origin of this highly anomalous behavior is thought to be the low droplet interfacial tension, gammaow, that occurs at the phase-inversion temperature, which results primarily in a substantially increased contact angle between the glycine critical nucleus and the droplet interface. This may present a paradigm shift in crystallization strategies through the use of tunable contact-angle nucleators.     

X-ray diffraction studies and interstitial model for liquid water

Samoilov's interstitial model for liquid water is considered. It is shown that geometrically different frameworks and different positions of cavity molecules lead to comparable degrees of agreement with the experimental radial distribution function. The meaning and the limits of these agreements are discussed.     

High temperature X-ray diffraction studies of the crystallization process of thin amorphous films with the chemical composition CrSi2.57

The crystallization process of amorphous thin films with the chemical composition CrSi_2.57 has been investigated by means of high temperature X-ray diffractometry. The crystallization of the amorphous as-deposited films takes place in two stages; in the first stage CrSi₂ is formed and in the second Si, resulting in a two component nano-disperse structure. The results are in agreement with investigations of the thermopower and the electrical conductivity [5, 6].     

DSC and X-ray studies on side-chain crystallization of comb-like polymers

Thermal properties of acrylate and methacrylate monomers containing long-fluorocarbon chains (H(CF₂)_nCH₂OCOCH=CH₂, (F_nA) and H(CF₂)_nCH₂OCOC(CH₃)=CH₂, (F_nMA), wheren=6, 8, 10) and their comb-like polymers have been investigated by differential scanning calorimeter (DSC) and X-ray diffraction. The comb-like polymers (PF₁₀A and PF₁₀MA) with sufficiently long-fluorocarbon chains showed a simple melting and crystallizing behavior. For the fusion of PF₁₀A in 1st heating, enthalpy change H _f was 18 kJ mol^–1 and entropy change S _f was 45 J K^–1 mol^–1, while for PF₁₀MA the values H _f and S_f were 5.3 kJ mol^–1 and 14 J K^–1 mol^–1, respectively. Melted PF₈A crystallized slowly, whereas PF₈MA with same fluorocarbon chain and also both of PF₆A and PF₆MA with shorter fluorocarbon chains can hardly crystallize by the aggregation of side-chains. Effects of the length of side-chain and the flexibility of main chain on the side-chain crystallization of comb-like polymers are clear. Crystallization process of the methacrylate monomers was sensitively affected by the scanning rate of DSC measurement and the length of fluorocarbon chains.     

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber have revealed that for the catalysts obtained by the reduction of preactivated samples, no complete reduction of platinum takes place.

---

, , , .