Emulsion Crystals Research Articles

Definition of a model fat for crystallization‐in‐emulsion studies

AbstractNumerous food products are dispersed in droplet emulsions in which fat is partially crystallized. A model fat allowing the study of crystallization in emulsion, obtained by the mixing of two fats (one solid and one liquid at room temperature) with simple triacylglycerol (TG) composition, is defined and characterized. Cocoa butter (CB), a vegetable fat mainly composed of monounsaturated long‐chain fatty acids (POP, POST, StOSt, where P=palmitic, O=oleic, St=stearic), and miglyol, a synthetic oil made from capric and caprylic fatty acids, were chosen, respectively. The thermal behaviors of CB, miglyol, and their mixtures are studied using high‐sensitivity differential scanning calorimetry (DSC). The CB/miglyol ratio was optimized (i) in order to make stable emulsions as a function of time, (ii) so that the mixture displays several solid phases on cooling that result from CB polymorphism, and (iii) in order to keep, even at low temperature, a liquid moiety facilitating the phase transitions. The CB 75%/miglyol 25% composition is defined as the model mixture. This mixture is characterized on cooling at 0.5°C/min by coupled X‐ray diffraction as a function of temperature and DSC experiments. First and α 2L (49.3 Å) variety is formed. Then, co‐crystallization of both CB and miglyol TG shows the simultaneous formation of longitudinal stackings of 44.5 and 34.5 Å with a lateral organization of β′ form. An unusual TG packing corresponding to compound formation is proposed to explain the observation of a 34.5 Å long‐spacing. The crystallization behavior of the model fat mixture dispersed in emulsion droplets is also monitored in order to validate its use.

Use of artificial neural networks to predict quaternery phase systems from limited experimental data

The aim of the present work was to develop a method for predicting the phase behaviour of four component systems consisting of oil, water and two surfactants from a limited number of screening experiments. Investigations were conducted to asses the potential of artificial neural networks (ANNs) with back-propagation training algorithm to predict the phase behaviour of four component systems. Three inputs only (percentages of oil and water and HLB of the surfactant blend) and four outputs (oil in water emulsion, water in oil emulsion, microemulsion, and liquid crystals containing regions) were used. Samples used for training represented about 15% of the sampling space within the tetrahedron body. The network was trained by performing optimization of the number and size of the weights for neuron interconnections. The lowest error was obtained with 15 hidden neurons and after 4500 training cycles. The trained ANN was tested on validation data and had an accuracy of 85.2–92.9%. In most cases the errors in the prediction were confined to points lying along the boundaries of regions and for the extrapolated predictions outside the ANNs ‘experience’. This approach is shown to be highly successful and the ANNs have proven to be a useful tool for the prediction of the phase behaviour of quaternary systems with less experimental effort.

Phase Sensitive Microwave Absorption Studies on AgBr<sub>1-x</sub>I<sub>x</sub>Emulsion Crystals

The influence of phase boundaries on the photoelectron lifetime of T-grain emulsion crystals is examined with the microwave absorption method. For the measurements, AgBr1−xIxT grains with a core-shell and a so-called “gradient” structure were used. The core-shell ratio, the grain volume, and the iodide content of the core were varied. The microwave absorption measurements indicated that a maximum photoelectron lifetime can be reached for a special combination of these parameters. In the case of core-shell T grains, maximum values were found for a core-shell ratio of 1:1 and iodide contents x > 0.08. For iodide values x < 0.02 “gradient” grains lead to the highest photoelectron lifetimes. A model is proposed to explain the behavior of the structured grains influenced by the interplay of the geometrical grain structure and the iodide content.

Surfactant Micelles, Liposomes, and Liquid Crystals in Emulsions and Microemulsions

Surfactant Micelles, Liposomes, and Liquid Crystals in Emulsions and Microemulsions

Crystallization kinetics in oil-in-water emulsions containing a mixture of solid and liquid droplets

The presence of the polysaccharide xanthan is found to have little effect on the kinetics of crystallization in emulsions containing a mixture of supercooled liquid and crystalline n-hexadecane droplets. When taken together with complementary creaming measurements on similar xanthan-containing emulsions, which are sensitive to polysaccharide concentration, this result appears to be possibly at variance with a crystallization mechanism based solely on collision-induced interdroplet heterogeneous nucleation.

Purification of molecular mixtures below the eutectic by emulsion crystallization

MELT crystallization1 is used increasingly by the chemical industry to purify organic compounds, in part because of the availability of new processing techniques2 and in part because of the commercial and legislative pressures demanding that such compounds be supplied with precisely defined compositions. At present, purification is generally achieved by a succesion of steps involving freezing on a cooled surface followed by partial melting3. As an alternative, we have been examining the process of emulsion crystallization4, in which a melt is crystallized within emulsified droplets so that homogeneous nucleation occurs at a lower rate than in a bulk melt. This approach requires no special equipment or solvents, and so offers the possibility of purification at low capital and operating costs. Here we report the use of this method to purify mixtures of meta and para chloronitrobenzene (m- and P-CNB) below their eutectic temperature at compositions where bulk crystallization would yield a mixture of pure m- or P-CNB and a m/p combination of the eutectic composition. Adding seed crystals of m-CNB to various m/p mixtures below the eutectic composition results in the formation of crystals highly enriched in m-CNB, while the p-CNB remains primarily in the emulsion phase. Thus emulsion crystallization has the potential to 'break' the eutectic, which otherwise presents a barrier to the separation of eutectic-forming mixtures.

Surfactant Micelles, Liposomes, and Liquid Crystals in Emulsions and Microemulsions

Surfactant Micelles, Liposomes, and Liquid Crystals in Emulsions and Microemulsions

J-aggregates of cyanine dye molecules adsorbed on the surfaces of AgBr emulsion crystals

Photosensitive thiacarbocyanine dye adsorbed on practical photographic emulsion AgBr microcrystals has been visualized by ultra-low energy scanning electron microscopy at room temperature. The dye is observed in stripes along the [210] and/or [120] direction on the AgBr (001) surface, which indicates that the dye molecules nucleate and grow with a certain epitaxial relation in respect with the AgBr lattice. The stripes become to a patch with increasing surface coverage. Using atomic force microscopy the stripes or patches are found to be not always monolayer. It is concluded by taking account of results of analytical color fluorescence electron microscopy that they are constructed with photoelectrically separated J-aggregate particles.

Influence of triglyceride composition on crystallization kinetics of model emulsions

Melt crystallization of trimyristin was investigated in colloidal systems, using magnetic resonance imaging (MRI) and differential scanning calorimetry (DSC). Alterations in crystallization behavior were produced by adding various percentages of trilaurin to the emulsion. Crystallization rates were studied as a function of time in fat/water emulsions (40:60, v/v) containing 0·5% Tween 80 and 0·2% xanthan gum to prevent creaming. Using MRI, oil weighted images followed crystallization in the trimyristin emulsions containing 0, 10 and 20% (volume per oil phase volume) of trilaurin, respectively. Localized spectroscopy, using a stimulated echo sequence, was used to determine the crystallization at different locations in (40:60) trimyristin emulsion samples. The addition of trilaurin to the trimyristin emulsion changed the crystallization pattern. Spectra recorded from the top, center and bottom showed a relatively abrupt crystallization pattern in the (40:60) trimyristin emulsion, whereas the trilaurin containing emulsions exhibited a longer time frame for crystallization. Phase behavior was also assessed using DSC. Nucleation and subsequent crystallization in bulk or within the droplets in the emulsions were detected by isothermal heat evolution. The isothermal DSC results paralleled results obtained with MRI. The results suggested that the crystallization pattern was altered as a function of the triglyceride composition of the oil phase.

Destabilization and fat crystallization of whippable emulsions (toppings) studied by pulsed NMR

AbstractThe role of lipid surfactants in toppings has been investigated. Based on low‐resolution pNMR analysis it seems that part of the fat phase in toppings is present in a supercooled state induced by lipid‐protein interactions. Upon reconstitution in cold water, protein is desorbed from the fat globule surface and dissolves into the water, thereby eliminating the protein‐induced supercooling of the fat. Subsequently, spontaneous fat crystallization takes place which can be followed by pNMR measurements. These phenomena result in an increase in the viscosity of the reconstituted emulsion. The surfactants usually used in toppings (e.g. propylene glycol monostearate) act as destabilizing factors in the reconstituted topping emulsion, accelerating (i) protein desorption from the fat globule surface, and (ii) the crystallization rate of coalesced fat. The fat crystallization process seems to be important for the texture and foam stability of whipped toppings.

The photolysis of small silver halide particles

Monolayer coatings of monodisperse silver halide microcrystals of general formula AgCl x Br 1- x with 0 ≼ x ≼ 1, were prepared and measurements carried out in order to determine the efficiency of photolysis. The effect of crystal size was studied: it is well known that the speed of photographic emulsions increases with the size of the emulsion crystals. Crystal edge length was varied from 0.3─1.0 μm. It was shown that, within this range, size has no effect on the quantum yield of photolysis. The speed increase therefore arises simply because larger crystals collect more photons, and the minimum number of photons required to make a crystal developable is attained more rapidly. The effects of sensitization were studied: it was shown that the effect of gold is not to be understood purely in terms of the latent image being smaller if it is composed of gold rather than silver, but that in addition the efficiency of photolysis increases. The results of the investigation are shown to be in agreement with the Gurney─Mott model. The remarkable difference in hole self-trapping at low temperatures between AgCl and AgBr is shown to account for differences in photo­graphic behaviour.

Liquid crystals in emulsions, creams, and gels containing ethoxylated sterols as surfactant.

Depending on the concentration and the hydrophilicity of the surfactant, different mesophases have been demonstrated by X-ray analysis, polarizing microscopy and transmission electron microscopy of freeze-fractured samples. These mesophases participate in the microstructure of ternary mixtures. Mixtures of sterol-PEG5- and stereol-PEGlO-ether form lamellar liquid crystals which are organized into multilamellar vesicles with a size of up to several microns. At low concentrations of the surfactant the ternary systems consist of fluid emulsions of liquid crystalline vesicles and droplets of liquid paraffine dispersed in the outer hydrous phase. With increasing concentrations of the surfactant the mixtures become creamy and semisolid but remain emulsions with an increased volume ratio of the inner phase. The phase diagram of mixtures with sterol-PEG16-ether shows three different regions of liquid crystals: lamellar liquid crystals of planar arrangement at high concentration of the surfactant, a hexagonal mesophase with dispersed liquid paraffine and a ringing gel of close-packed mixed micelles. The higher the volume fraction of the liquid paraffine the larger are the oily droplets which are dispersed in the outer liquid crystalline phase of the close-packed micelles. The phase diagram of the most hydrophilic sterol-PEG25-ether is similar to that of sterol-PEG16-ether except for the absence of lamellar liquid crystals.

Silver Halide Crystals in New Type Photographic Emulsions

Silver Halide Crystals in New Type Photographic Emulsions

A Contribution to Interpretation of the Photographic Characteristic Curve

The problem of the photon sensitivity of emulsion crystals is reviewed and is seen to rest on interpretation of the characteristic curve. A partial-development technique for the identification of grains hearing latent image is used to determine characteristic curves for effectively mono-sized classes of grains in a fast medical X-ray film given monochromatic exposure. The characteristic curve of a pure-bromide nominally monodisperse emulsion is also shown for monochromatic exposure. Characteristic curves of the two emulsions are analyzed according to models which assume, respectively, a unique photon sensitivity and efficiency factor, and the existence of a spread of effective photon sensitivities. Conclusions are drawn concerning the success of the partial development technique and of the analytical methods, the photon sensitivities found and the minimum size of latent image.

Latent Image Fading in AgBr Emulsion Crystals as a Function of the Composition of the Gelatin Binder

AbstractLatent-image fading and the anti-fading action of different gelatin, gelatin fragment. amino acid and other addition agent were inve tigated in AgBr hydrosols. Quite mall fragment and even individual amino acid uch a glycin were quite ffective antifader. These agent also caused photographIc ensitization. Both sen itization and anti-fading action were accounted for by the same mechanism: the tabilization of latent-image centre or ub-centres. being more effective the smaller the centre.

A method to identify nuclear reactions registered in ionographic detectors

A method is established to examine all compatible assignations of charge and mass number to the target and emergent prongs of an event registered in an ionographic detector (such as nuclear emulsion or silver chloride crystals) under the requirements of conservation of momentum and total energy. The kinematical parameters corresponding to the most likely configurations are determined by a least-squares process. For the accepted hypothesis, the probability associated to the minimized value of the chi-square function and to the number of degrees of freedom is computed. The correctness of the method is tested by means of simulated events.

Coating sections for electron microscopic autoradiography: a stripping technique using liquid emulsion.

A coating technique for electron microscope autoradiography is described which combines the advantage of forming an emulsion film by a dipping method with the ease of coating sections already on grids. Sections are coated so that a formvar support film separates the section and the emulsion crystals. This intermediate layer of formvar ensures a random distribution of the emulsion crystals. Using light gold sections, Ilford L-4 emulsion and Microdol-X development, the resolution of this technique, as determined by the half distance method, was 150 nm. The additional layer of formvar slightly reduced the image quality with biological samples in the electron microscope. This technique has a minimal loss of resolution and image quality for moderate resolution electron microscope autoradiography.

Development by Means of Electrode Reduction of Individual Silver-Halide Emulsion Crystals*

"Development by Means of Electrode Reduction of Individual Silver-Halide Emulsion Crystals*." The Journal of Photographic Science, 23(3), pp. 131–132

Absorption Spectra of Sensitizing Dyes Adsorbed to Silver Bromide and to Silver Iodobromide

The reflectance spectra have been obtained for three thiacarbocyanine dyes adsorbed to silver bromide emulsion crystals having either 111 or 100 faces. The effects of digestion, crystal face, incorporated iodide, and the adsorbed organic stabilizer 2-methylthio-4-hydroxy-6-methyl-I,3,3a,7-tetraazaindene, on dye aggregation have been measured.On 111 faces the dyes form conventional M-, H- and J-bands, but the results are complex as the bands are extremely sensitive to changes in conditions: they are dependent on iodide, stabilizer and the time of addition of dye in relation to digestion. Digestion or incorporated iodide enhances J-aggregation, and iodide gives the J-aggregate a bathochromic shift of 5-10 nm. Both these effects can be explained by postulating that the 111 face is relatively rough, and has nucleation centres which initiate dye aggregation. Iodide provides particularly good nucleation centres.By contrast, on 100 faces the dye aggregation is simple in that the dyes form only two main peaks (517 nm and 595 nm), and these are unaffected by any of the variables mentioned above. The relative heights of the two peaks are also unaffected by changes in the dye concentration. The assignment of the peaks on this surface is more difficult but they are consistent with a herringbone structure for the dye aggregate with two molecules per unit cell.

Determination of Energy Levels in AgBr Emulsion Crystals from Optical Measurements

AbstractThe width of the forbidden energy gap and the position of the top of the valence band cannot be determined as precisely for AgBr at room temperature as for many ionic crystals. Some choices for these parameters, which are necessarily arbitrary, are given here to provide good agreement with the variety of optical and photographic measurements made with small AgBr crystals. Changes of the energy levels with temperature, iodide incorporation, and the presence of surfaces were measured. Surface states located at lattice ions are too shallow to act as electron traps or to be detected in our optical absorption experiments. Luminescence of pure AgBr was investigated at 77°K. The luminescence centre is at an electron trap which is 0.75 eV below the bottom of the conduction band. This centre, which is stable when formed by exposures at 77°K, is the same as the unstable latent image centre at room temperature investigated by Webb and is thought to be a single electron trapped at two silver ions. The stable ...