Emulsion Crystals Research Articles

Effect of water on self-assembled tubules in β-sitosterol + γ-oryzanol-based organogels

Mixtures of β-sitosterol and γ-oryzanol form a network in triglyceride oil that may serve as an alternative to the network of small crystallites of triglycerides occurring in regular oil structuring. The present x-ray diffraction study investigates the relation between the crystal forms of the individual compounds and the mixture in oil, water and emulsion. β-Sitosterol and γ-oryzanol form normal crystals in oil, in water, or in emulsions. The crystals are sensitive to the presence of water. The mixture of β-sitosterol + γ-oryzanol forms crystals in water and emulsions that can be traced back to the crystals of the pure compounds. Only in oil, a completely different structure emerges in the mixture of β-sitosterol + γ-oryzanol, which bears no relation to the structures that are formed by both individual compounds, and which can be identified as a self-assembled tubule (diameter 7.2±0.1 nm, wall thickness 0.8±0.2 nm).

Crystallisation from Water-in-Oil Emulsions As a Route to Spherical Particulates: Glycine and the Hydrochloride Salts of Glutamic Acid and Ephedrine

Emulsion crystallization has been reported as an approach to controlling particle properties, and is part of a wider set of techniques that can be used to form spherical particles. In the pharmaceutical industry, spherical particles are known to present distinctive advantages in terms of flow and compression properties, for example over needles or laths. This study sought to define a possible working space for the development of emulsion crystallisation of materials that could mimic pharmaceutically active compounds. Crystallisation of three water-soluble materials, glycine, l-glutamic acid hydrochloride, and ephedrine hydrochloride from water-in-oil emulsions is explored. In particular, work on these compounds shows that the combined importance of stirring and surfactant and templating additive choice is evident in developing a practical route to utilising this technology. It is also evident that the relative solubility of the solute in the two liquid phases may totally preclude the use of the drops as c...

Ammonium Dinitramide (ADN)–Prilling, Coating, and Characterization

AbstractAmmonium dinitramide (ADN) is the promising oxidizer, which is expected to be applied, e.g., in solid rocket propellants. The manufacturing of spherical ADN particles (the so‐called ADN‐Prills) with useful morphology and reproducible quality is realized by means of the emulsion crystallization process.

Effects of high pressure on anhydrous milk fat crystallization in emulsion

Anhydrous milk fat crystallization was compared either in bulk phase or in oil in water emulsion by studying melting curves obtained by calorimetry measurements. Emulsions were submitted to a high pressure (HP) treatment (200 MPa/10 min). An aging period of 72 h was required to obtain the highest amount of crystallized fat at 4 °C. Emulsification promoted the crystallization of low melting point (LMP) triglycerides. The effect of HP on anhydrous milk fat crystallization depended on the aging time. For short aging periods (30 min and 1 h), HP treatment favored the crystallization of LMP triglycerides, thus amplifying the effect of emulsification compared with the crystallization in bulk phase. However, for a long aging time, i.e. 48 h, the amounts of crystallized matter in emulsion with or without HP treatment were comparable. This result was interpreted in terms of a different polymorphic form crystallizing under HP.

Melting Behavior of Shear-Induced Crystals in Dense Emulsions as Investigated by Time-Resolved Light Scattering

The crystal growth of dense and almost monodisperse colloids has been investigated during recent years, but less is known about the melting behavior. The current study thus focuses on this topic. Monodisperse hard spheres were found to crystallize for certain concentrations (49-58 vol %), after sufficiently long times. The characteristics of the crystal growth change when the colloidal particles are polydisperse. Finally, when the size distribution function of the particles is broad enough, the crystallization no longer took place. Dense oil-in-water emulsions with polydispersities of around 10% were successfully produced, and in a first approximation, these emulsions behaved like hard spheres. The polydispersity of the emulsions was sufficiently high to avoid crystallization in equilibrium but low enough to induce a disorder-to-order transition under shear. The formed crystals started to melt once the shear was discontinued. The melting behavior of these "oil droplet crystals" was investigated by means of time-resolved static light scattering experiments, and it was found that crystallization could be induced in a concentration regime between 46 and approximately 74 vol %. The melting behavior of these crystals depended strongly on the concentration. The typical melting times ranged from a few seconds to several hours or days when the concentration was increased. It was speculated that this phenomenon could be explained by the strong dependence of the mobility of the oil droplets on the volume fraction, as verified by dynamic light scattering experiments on oil-in-water emulsions in a similar concentration regime.

Synthesis and kinetic analysis of isothermal and non-isothermal decomposition of ammonium dinitramide prills

Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method of Vyazovkin were used to investigate the dependence of activation energy (E a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived from isothermal data. A strong dependence of E a with α is observed for the ADN prills. All the methods showed an initial increase in E a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol−1, respectively.

OIL RECOVERY WITH NOVEL SKIMMER SURFACES UNDER COLD CLIMATE CONDITIONS

ABSTRACT Increasing oil exploration, production and transport in Arctic waters will increase the risk of an oil spill occurring in cold and ice-infested waters. The mechanical oil spill recovery equipment currently used in warmer waters was not designed to collect much more viscous oils, or oil-ice mixtures. The presence of ice crystals in oil emulsions affects the adhesion processes between an oil slick and the surface of an oleophilic skimmer and prevents oil from being efficiently recovered. Novel drum skimmer surface geometry and materials, tailored to the conditions present under cold climates, are expected to significantly increase the rate of oil recovery, reducing cost and risk. The objective of this project was to perform a comprehensive analysis of the adhesion between oil or ice-in-oil mixtures and various surface patterns and materials, under cold climate conditions. This knowledge was then applied to improve existing mechanical response equipment so that it can be applied efficiently under these conditions. The novel recovery surfaces that proved to increase the recovery efficiency of a drum skimmer up to two times in warm waters were also successful in cold climate conditions. In the first phase of the project, laboratory bench-scale tests of different surface materials were conducted, to determine contact angle and amount of oil adhered at sub-freezing conditions, with and without ice. It became clear that the physicochemical property that would be most significantly influence by cold climate conditions would be viscosity, and that the presence of ice would also have an important effect on viscosity, although to a varying degree depending on the initial oil viscosity. Neoprene was the best material surface, of those tested here, for adhering oil even under oil/ice conditions. Based on the results of the laboratory tests at subfreezing conditions, we selected materials and surface patterns with the highest oil recovery potential under cold climate conditions, and performed field scale oil spill recovery tests with three different oils at the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL), located in Hanover, NH. This provided valuable information about the correlation between the laboratory tests and full scale experiments. It also demonstrated the potential of the skimmer modifications under conditions similar to response operations. The field tests were very successful, with high rates of oil recovery under cold climates, with and without ice present. However, the presence of ice does decrease the overall rate of oil recovery to some extent. The outcome of this project advanced our understanding of the adhesion of oil and oil emulsions (water containing and ice-containing) to recovery surface material under cold climate conditions. This research will facilitate selection of materials and surface configurations that result in significantly higher recovery rates of oil spills in cold and ice-infested waters. This will ultimately lead to a faster oil spill cleanup and greater protection of natural resources.

Stop-and-return DSC method to study fat crystallization

Differential scanning calorimeters have frequently been used to study the isothermal crystallization kinetics of fats and oils. In some circumstances (e.g. start of crystallization during cooling to the crystallization temperature, crystallization in emulsion) this straightforward approach is not applicable. This paper describes an indirect DSC method for determination of the crystallization kinetics under these ‘difficult’ circumstances. The principle is to stop the crystallization at different moments during the isothermal crystallization and raise the sample temperature. The amount of heat released is then used as a measure for the amount of crystallization and plotted as function of time. Combination of the stop-and-return method with the direct method may sometimes be used to save on measurement time. Stop-and-return experiments can furthermore be used to gain more insight in the crystallization mechanism based on the fact that different polymorphic forms and fractions have different melting temperatures.

Nucleation Rate Measurement of Colloidal Crystallization Using Microfluidic Emulsion Droplets

An emulsion crystallization method has been demonstrated to measure the nucleation rate of a thermoresponsive colloidal poly-N-isopropylacrylamide (PNIPAM) system. The colloidal PNIPAM suspension was injected into a microfluidic flow-focusing device to generate monodispersed droplets in oil. The temperature was controlled to fine tune the volume fraction of the PNIPAM particles, and the microfluidic flow rate was varied to change the droplet sizes, thus altering the nucleation volume. Using independent droplets, we can isolate the nucleation events to eliminate the interactions among crystallites that existed in bulk or large droplet systems. Therefore, we were able to carry out accurate nucleation rate measurements of colloidal crystals. This emulsion crystallization method is promising for bridging the gap among theories, simulations, and experiments for nucleation kinetics studies.

Kinetically Stable Aqueous Lipid Dispersions Prepared by Crystallization Processes

Lipids provide a wide range of functional properties utilized in technical applications, and the mechanisms usually are based on the physical properties of the liquid‐crystalline phases. Even the solid state of lipids can sometimes provide similar functions, which are described in this article. Crystallization from an aqueous dispersion of the lamellar liquid‐crystalline phase of monoglycerides can form hydrophilic lipid crystals, which are able to attach large proportions of water to the dominating surfaces of the leave‐shaped crystals formed by the polar head group planes. Such lipid crystal dispersions have been utilized as a general ointment base and as stabilizers in food applications. Many lipid‐based emulsions are prepared by cooling during a mixing process. A general mechanism for stabilization of such emulsions is the formation of crystals of polar lipids at the oil/water interface. These lipid crystals form an interfacial film, which expose hydrophilic surfaces toward the water phase and hydrophobic surfaces toward the inner oil core. The interfacial tension versus temperature at the corresponding oil/water interface starts to decrease abruptly at the same temperature as crystals of the polar lipid start to form in the oil phase, as identified by x‐ray diffraction. The crystal formation in the corresponding binary system triglyceride oil/polar lipid followed in the polarizing microscope shows a simple eutectic behavior. The polar lipid crystal formation at the oil/water interface requires that the triglyceride oil/polar lipid composition of the binary system corresponds to the polar lipid side of the eutecticum. Examples of both oil‐in‐water and water‐in‐oil emulsions formed in this way are described. Other aspects of lipid crystals in emulsions, which involve the oil core, are also discussed. An interesting phenomenon is the formation of a beta‐crystal gel state, which recently has been characterized.

Impact de la cristallisation des corps gras sur les propriétés des produits finis

In various food products, the fat phase which is almost essentially composed of triacylglycerols is found in a crystallized form at temperature of use or of storage. The fat physical characteristics influence the rheological properties and the stability of the products. In food, the fat phase is frequently found in a dispersed form either as oil in water emulsions (ice cream, whipped topping) or as water in oil emulsion (butter, margarine). The mechanism of fat crystallisation is different in the bulk phase and in emulsified systems so that the fat behaviour in emulsion can not simply be deduced from that in the bulk phase. In particular, crystallization in emulsion depends on various parameters such as the fat globule size and the presence of surfactants (proteins and low molecular weight emulsifiers). Moreover, fat crystals play a major role in the emulsion stability, i.e., by stabilizing water in oil emulsions and destabilizing oil in water emulsions. Conversely, crystals are implied in the formation of a fat network of partially coalesced droplets that participates to the foam stabilization in aerated food products based on oil in water emulsions.

A mathematical model of crystallization in an emulsion

A mathematical model incorporating many of the important processes at work in the crystallization of emulsions is presented. The model describes nucleation within the discontinuous domain of an emulsion, precipitation in the continuous domain, transport of monomers between the two domains, and formation and subsequent growth of crystals in both domains. The model is formulated as an autonomous system of nonlinear, coupled ordinary differential equations. The description of nucleation and precipitation is based upon the Becker-Doring equations of classical nucleation theory. A particular feature of the model is that the number of particles of all species present is explicitly conserved; this differs from work that employs Arrhenius descriptions of nucleation rate. Since the model includes many physical effects, it is analyzed in stages so that the role of each process may be understood. When precipitation occurs in the continuous domain, the concentration of monomers falls below the equilibrium concentration at the surface of the drops of the discontinuous domain. This leads to a transport of monomers from the drops into the continuous domain that are then incorporated into crystals and nuclei. Since the formation of crystals is irreversible and their subsequent growth inevitable, crystals forming in the continuous domain effectively act as a sink for monomers "sucking" monomers from the drops. In this case, numerical calculations are presented which are consistent with experimental observations. In the case in which critical crystal formation does not occur, the stationary solution is found and a linear stability analysis is performed. Bifurcation diagrams describing the loci of stationary solutions, which may be multiple, are numerically calculated.

Multiplexed holographic gratings for fabricating 3D photonic crystals in BB640 photographic emulsions

Three multiplexed holographic gratings were used to fabricate 3D photonic crystals without complete band gap using ultra-fine grain holographic emulsion as the storage material. Theoretical and experimental studies were carried out in order to characterize the crystals. Good agreement between theory and experimental results was obtained, showing that it is possible to obtain a band-pass filter for a fixed direction of illumination.

Fat crystallization in complex food emulsions: Effects of adsorbed milk proteins and of a whipping process

Crystallization of fat droplets in complex emulsions, which differed only by the initial structure of proteins, was studied by differential scanning calorimetry, before and after application of a whipping process. Upon cooling at 5 or 1°C min−1, the temperature needed to initiate fat crystallization was lower, and one more distinguishable crystallization peak was detected in emulsions containing caseins, in comparison with the emulsion containing pure whey proteins. Furthermore, the whipping process was accompanied by more protein depletion from the fat droplet surface, less resistance to coalescence, and a lower supercooling effect in the emulsion based on pure whey proteins.

Thermal and Structural Behavior of Milk Fat: 3. Influence of Cooling Rate and Droplet Size on Cream Crystallization

Crystallization of triacylglycerols (TG) within milk fat globules of creams is studied with an instrument coupling time-resolved synchrotron X-ray diffraction (XRDT) at both small and wide angles and high-sensitivity differential scanning calorimetry (DSC) at cooling rates of −3 and −1°C/min from 60 to −10°C and compared to that of the anhydrous milk fat (AMF). Simultaneous thermal analysis permits correlation of the formation of the different crystalline species monitored by XRDT to the DSC events. Under the above cooling conditions, milk fat TG sequentially crystallize, within the globules, from about 19°C, in three different lamellar structures with double-chain length (2L) stackings of 47 and 42 Å and a triple-chain length (3L) stacking of 71 Å, all of α type, which are correlated to two or three overlapped exothermic peaks recorded by DSC. Compared to what is observed for AMF, TG crystallization in emulsion (i) favors sub-α formation at low temperature and (ii) induces layer stacking defects in 3L crystals. Subsequent heating at 2°C/min shows numerous structural rearrangements before final melting, confirming that (i) cooling at −1°C/min leads to the formation of unstable crystalline varieties in the dispersed state and (ii) a monotropic transition α→β′ takes place. Similar behavior is observed for cooling at −3°C/min and subsequent heating. An overall comparison of the thermal and structural properties of the crystalline species formed as a function of the cooling rate, between >1000 and 0.15°C/min, and stabilization time at 4°C is given. Depending on the cooling rate, at least five crystalline subcell species are observed at wide angles, α and sub-α, two β′ and one β. At small angles, at least six lamellar stackings are identified, three 3L and three 2L. However, a single subcell packing (e.g., α) might correspond to several longitudinal chain stackings, demonstrating the usefulness of the small-angle XRD technique. Reconstituted emulsions homogenized under different pressures are used to determine the influence of droplet size on crystallization. The decrease of droplet size induces (i) a higher supercooling/supersaturation and (ii) a higher disorder and/or a smaller size of TG crystals within the emulsion droplets. At the supramolecular scale, polarized light microscopy shows that various cooling rates applied in situ using a temperature-controlled stage directly influence crystal sizes and their type of organization within milk fat globules. The faster the cooling rate, the smaller the size of the crystals within the globules.

Thermal and Structural Behavior of Milk Fat3. Influence of Cooling Rate and Droplet Size on Cream Crystallization

Crystallization of triacylglycerols (TG) within milk fat globules of creams is studied with an instrument coupling time-resolved synchrotron X-ray diffraction (XRDT) at both small and wide angles and high-sensitivity differential scanning calorimetry (DSC) at cooling rates of -3 and -1 degrees C/min from 60 to -10 degrees C and compared to that of the anhydrous milk fat (AMF). Simultaneous thermal analysis permits correlation of the formation of the different crystalline species monitored by XRDT to the DSC events. Under the above cooling conditions, milk fat TG sequentially crystallize, within the globules, from about 19 degrees C, in three different lamellar structures with double-chain length (2L) stackings of 47 and 42 A and a triple-chain length (3L) stacking of 71 A, all of alpha type, which are correlated to two or three overlapped exothermic peaks recorded by DSC. Compared to what is observed for AMF, TG crystallization in emulsion (i) favors sub-alpha formation at low temperature and (ii) induces layer stacking defects in 3L crystals. Subsequent heating at 2 degrees C/min shows numerous structural rearrangements before final melting, confirming that (i) cooling at -1 degrees C/min leads to the formation of unstable crystalline varieties in the dispersed state and (ii) a monotropic transition alpha-->beta' takes place. Similar behavior is observed for cooling at -3 degrees C/min and subsequent heating. An overall comparison of the thermal and structural properties of the crystalline species formed as a function of the cooling rate, between >1000 and 0.15 degrees C/min, and stabilization time at 4 degrees C is given. Depending on the cooling rate, at least five crystalline subcell species are observed at wide angles, alpha and sub-alpha, two beta' and one beta. At small angles, at least six lamellar stackings are identified, three 3L and three 2L. However, a single subcell packing (e.g., alpha) might correspond to several longitudinal chain stackings, demonstrating the usefulness of the small-angle XRD technique. Reconstituted emulsions homogenized under different pressures are used to determine the influence of droplet size on crystallization. The decrease of droplet size induces (i) a higher supercooling/supersaturation and (ii) a higher disorder and/or a smaller size of TG crystals within the emulsion droplets. At the supramolecular scale, polarized light microscopy shows that various cooling rates applied in situ using a temperature-controlled stage directly influence crystal sizes and their type of organization within milk fat globules. The faster the cooling rate, the smaller the size of the crystals within the globules.

Computer simulation of selective absorption of radiation by the components of a light-scattering layer

A method of calculating the partial characteristics of radiation absorption by the components of light-scattering disperse layers is proposed. This method is based on statistical modeling (the Monte Carlo method). The absorptivities of photographic gelatin and silver bromide microcrystals and the corresponding distributions of the absorbed energy over the layer thickness are calculated using the example of an interaction between actinic radiation and silver halide photographic layers in the wavelength range λ=200–440 nm. The following structural parameters of the photographic layer are used in the calculation: the mean size of emulsion crystals d=0.5 μm; the polydispersity C V =25%; the volume concentrations C V =10, 20, and 30%; and the thickness of the emulsion layer H=10 μm.

Characterizing cocoa butter seed crystals by the oil‐in‐water emulsion crystallization method

AbstractUnambiguous quantitative evidence for the catalytic action of seed crystals in cocoa butter is presented. We used an ultrasound velocity technique to determine the isothermal growth of solid fat content in cocoa butter oil‐in‐water emulsions, in which the probability of finding a seed crystal in any one droplet was around 0.37 at 14.2°C. The upper limit for the size of seed crystals in West African cocoa butter was around 0.09 μm, the Gibbs free energy for nucleation was 0.11 mj m−2, and the concentration of seed crystals was in the range of 1016 to 1017 m−3. X‐ray diffraction measurements showed that emulsified cocoa butter crystallizes in the α polymorph and does not appear to transform to the β′ form within the first 25 min of crystallization. Primary nucleation events in cocoa butter emulsions are accounted for by seed crystals. Collision‐mediated nucleation, a secondary nucleation mechanism, in which solid droplets (containing seed crystals) catalyze nucleation in liquid droplets, is shown to account for subsequent crystallization. This secondary nucleation mechanism is enhanced by stirring.

Study on Preparation of a Low Density Polyethylene Particle by Emulsion Crystallization.

In this work, an emulsion crystallization was made to investigate the possibility of the preparation of fine particles. The method selected was intended to prepare a micron-sized low density polyethylene particle. Dodecanol as a theta solvent and diethylene glycol as a non-solvent were selected. Operating conditions, such as composition of solution, concentration of polyethylene, stirring speed, and temperature of the polymer solution were investigated. The polymer particles obtained by emulsion crystallization were spherical, with mean size ranging from 0.5 μm to 5 μm. As a result, we observed the instability of the emulsion for crystallization conditions. This instability has an effect on the mean diameter and particle size distribution of the prepared particles.

Monitoring fat crystallization in aerated food emulsions by combined DSC and time-resolved synchrotron X-ray diffraction

The thermal and structural evolutions associated to the fat crystallization in a whipped emulsion made from interesterified palm oil are monitored using a new instrument allowing simultaneous time-resolved synchrotron X-ray diffraction at both wide and small angles as a function of temperature (XRDT). This is performed simultaneously with high sensitivity differential scanning calorimetry (DSC) that is carried out in the same apparatus at scanning rates between 0. 01 and 10 K/min on the same sample (typical: 20 mg) in the −30 to +230 °C range. The thermal and structural properties of palm oil-based emulsions are also studied. It is found that the combination of these techniques allows the thermal monitoring of fat polymorphism even within the fat droplets at scanning rates of up to 5 K/min. The formation of α, β′ and β phases,and their transitions are followed simultaneously by DSC and XRDT allowing the identification of the thermal events recorded. It is shown that this interpretation is only possible when high resolution X-ray scattering at small angles and wide angles is coupled with DSC from the same sample.