Emulsions preparation

The role of surfactant in emulsion formation is crucial and is described in detail in Chapter 6. It reduces the oil-water interfacial tension, yow adsorption at the interface. The droplet size R is directly proportional to yow It enhances deformation and break-up of the droplets by reducing the Laplace pressure p, 

As a result of this interfacial tension gradient, surfactant molecules will diffuse to the regions with higher y, and they carry liquid with them (i.e. they force liquid in between the droplets) and this prevents coalescence (Marangoni effect). 

In comparison with previous studies, the systems studied by Pays et al. possess the advantage of being size-controlled and reproducible. This is an important property because, as demonstrated by the authors, the rate of release of double emulsions is strongly dependent on the colloidal size of the dispersed objects. The following notations are used to characterize the composition and properties of double emulsions  

Ch = initial concentration of the hydrophilic surfactant in the external water phase 

Pw is the density of the external water phase, g is the acceleration due to gravity (9.8 m/s ), and rjc is the viscosity of the continuous phase. Then, it becomes possible to determine the internal droplet volume fraction (/ , inside the globules according to the relation  

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The HLB system has made it possible to organize a great deal of rather messy information and to plan fairly efficient systematic approaches to the optimiza-tion of emulsion preparation. If pursued too far, however, the system tends to lose itself in complexities [74]. It is not surprising that HLB numbers are not really additive their effective value depends on what particular oil phase is involved and the emulsion depends on volume fraction. Finally, the host of physical characteristics needed to describe an emulsion cannot be encapsulated by a single HLB number (note Ref. 75). 

Kinetics and Mechanisms. Early researchers misunderstood the fast reaction rates and high molecular weights of emulsion polymerization (11). In 1945 the first recognized quaHtative theory of emulsion polymerization was presented (12). This mechanism for classic emulsion preparation was quantified (13) and the polymerization separated into three stages. 

Hexachloroethane has been suggested as a degasifter in the manufacture of aluminum and magnesium metals. Hexachloroethane has been used as a chain-transfer agent in the radiochemical emulsion preparation of propylene tetrafluoroethylene copolymer (152). It has also been used as a chlorinating agent in the production of methyl chloride from methane (153). 

The solubility of canthaxanthin in most solvents is low compared with P-carotene and P-apo-8 -carotenal. Oil solutions of canthaxanthin are red at all concentrations. Aqueous dispersions are orange or red depending on the type of emulsion prepared. 

The coacervation approach uses heating or chemical denaturation and desolvation of natural proteins or carbohydrates. As much as 85% of water-soluble drugs can be entrapped within a protein matrix by freeze-drying the emulsion prepared in this manner. For water-insoluble drugs, a microsuspension-emul-sion procedure has been suggested as a method of choice to achieve high drug payloads. 

Izquierdo, P., Esquena, J., Tadros, T.F., Dederen, C., Garcia, M.J., Azemar, N. and Solans, C. (2002) Formation and stability of nano-emulsions prepared using the phase inversion temperature method. Langmuir, 18 (1), 26-30. 

Sole, I., Maestro, A., Gonzalez, C., Solans, C. and Gutierrez, J.M. (2006) Optimization of nano-emulsion preparation by low-energy methods in an ionic surfactant system. Langmuir, 22 (20), 8326-8332. 

High-power mixture for emulsion preparation was required to obtain a stable emulsion of fatty acid and xanthate mixture. 

Monomer emulsion preparation, 76 286 Monomeric formaldehyde, properties of, 72 108t... 

Figure 1.9. Comparison between two bitumen-in-water emulsions prepared following (a) the classical protocol, (b) the protocol described in [134]. (Adapted from [134].)...

P. Izquierdo, J. Esquena, T.F. Tadros, J.C. Dederen, M.J. Garcia, N. Azemar, and C. Solans Formation and Stability of Nano-Emulsions Prepared Using the Phase Inversion Method. Langmuir 18, 26 (2002). 

Recently, the synthesis of nano-sized HA has been proposed via reverse-micro-emulsion preparation, which is reported to be effective for controlling the hydrolysis and polycondensation of the alkoxides of the constituents. Using this preparation route, the nanoparticles crystallize directly to the desired phase at the relatively low temperature of 1050 °C and maintain surface areas higher than 100 m g after calcination at 1300 °C for 2h [107-109]. 

Four 250 ml standard apparatus (round bottom flask, several inlets for stirrer, reflux condenser, nitrogen flux or vaccum, thermometer, heating bath) are filled each with 38 ml of distilled water and 405 mg (1.8 mmol) ammonium peroxodisuifate.To the fourth flask, additionally 90 mg of an alkylbenzene sulfonic acid sodium salt emulsifier (linear Cl 0-C13 aikyl chains, 70% in water) are added. After reaching an internai temperature of 80 °C,3 g of a monomer emulsion (prepared according toTabie 3.13) are added to each of the four batches. Within an induction phase of 15 min the reactions start. This is visuaiized by the pale blue coloration of the content of the flasks.Then the remaining monomer emulsion is added over a period of 3 h.The internal temperature has to be maintained at 80 °C during the whole reaction. After ail monomer emulsion has been added, the batches are heated at 80 °C for another 30 min.Then, the flasks are allowed to cool to room temperature. Now the reaction mixtures are adjusted to pH 8.5 by addition of 5% NaOH solution. 

Although Stokes law does not apply to particles so small that the Brownian movement influences the rate of gravitational settling, yet for the relatively coarse emulsions prepared in this way, no sensible error is introduced. 

Kind and Amount of Emulsifier Used. Rather extensive laboratory studies have been conducted to determine the characteristics of oil emulsions prepared with various emulsifiers. These studies have led to the use of such terms as quick breaking and tight emulsions. In view of the many factors known to influence the characteristics of an emulsion, such classifications would appear to be of doubtful significance under practical conditions. 

The oils were applied in the form of an aqueous emulsion prepared according to the tank-mixture method. Most of the time it is possible to approach a given oil deposit by proper adjustment of the concentration of oil in the spray mixture. The volume basis was used for the concentration of oil in the spray emulsion. The ingredients were emulsified and agitated by means of a high speed homomixer (made by Eppenbach, Inc., Long Island City, N. Y.). 

Water-in-oil emulsions prepared from Tween, Span, Aerosol-OT, and Pluronic industrial type emulsifying agents... 

Figure 3.4 Effect of polysaccharide on protein-stabilized emulsions. The diameter ratio, j43nuxtlire / J43protem is plotted against the molar ratio R (moles polysaccharide / moles protein). Here J43nuxtlire is average droplet diameter in fresh emulsion prepared with protein + polysaccharide, and d43pTOtQm is average diameter in emulsion stabilized by protein alone. Key , , legumin + dextmn (48 kDa) or legumin + dextran (500 kDa), respectively (0.5 w/v % protein, 10 vol% oil, pH = 8.0, /= 0.1 M) (Dickinson and Semenova, 1992) O, , asi-casein + pectinate and p-casein + pectinate at pH = 7.0, / = 0.01 M (2.0 w/v % protein, 40 vol% oil), respectively , p-casein + pectinate at pH = 5.5, / = 0.01 M (2.0 w/v % protein, 40 vol% oil) (Semenova et al, 1999). Reproduced from Semenova (2007) with permission.

Chuah, A.M., Kuroiwa, T., Kobayashi, I., Nakajima, M. (2009). Effect of chitosan on the stability and properties of modified lecithin stabilized oil-in-water monodisperse emulsion prepared by microchannel emulsification. Food Hydrocolloids, 23, 600-610. 

Figure 7.10 Effect of the thermodynamic incompatibility of otsi/p-casein + high-methoxy pectin (pH = 7.0, / = 0.01 M) on phase diagram of the mixed solutions and elastic modulus of corresponding casein-stabilized emulsions (40 vol% oil, 2 wt% protein), (a) (O) Binodal line for p-casein + pectin solution with critical point ( ) ( ) binodal line for asi-casein + pectin solution with critical point ( ). (b) Complex shear modulus G (1 Hz) is plotted against the pectin concentration (O) p-casein ( ) o i -casein. Dotted lines indicate the range of pectin concentration for phase separation in the mixed solutions. The pectin was added to the protein solution before emulsion preparation. Data are taken front Semenova et al. (1999a).

Table IV. Viscosity of emulsions prepared from pea protein...

On the basis of the above dimer formation model, a time course of the absorbance of Y-Dye (/4(f)) produced in an individual droplet has been analyzed [104]. The coupling reaction between QDI and Y-Cp is assumed to proceed at the oil-droplet/water interface (rate constant, kt) and the association equilibrium between the Y-Dye monomer and dimer is attained immediately upon the dye formation. In the actual experiments, QDI is oxidized partly by 02 dissolved in the water phase, so that Y-Dye is produced in a DBP droplet even before electrolysis of QDI. To correct this contribution, [Y-Dye] is defined as [Y-Cp]0 — [Y-Cp]j exp( — fc,[QDI]wf), where [Y-Cp]0 and [Y-Cp], are the Y-Cp concentrations at the emulsion preparation and t = 0 (before electrolysis), respectively. According to the... 

Figure C3.1.2 Comparison of lipase activities using an olive oil substrate emulsion prepared with different emulsifying agents. The lipase used in the reaction mixture was from C. rugosa (at 0.06 mg/ml) in the presence of 5% (w/v) each of gum arabic (triangles) or Triton X-100 (diamonds). Reaction progress analysis was obtained using titrimetry. Broken lines represent estimation of initial reaction rates.

Monodisperse emulsions, prepared by the double-jet method, have a narrow range of grain sizes of uniform shape. The grains can be either cubic or octahedral, depending on the conditions of preparation. 

Emulsions prepared with gelatin that had been treated to minimize sensitizing impurities have relatively low sensitivities for exposures made in air, particularly at low irradiances. They show pronounced low intensity reciprocity failure (LIRF). The pure silver bromide emulsions do not show high intensity reciprocity failure (HIRF) for direct development (65,66), but may do so for physical development (66). Faelens obtained HIRF in silver chloride emulsions for both physical development and the same developer he used for direct development of his silver bromide emulsion (67). Silver chloride emulsions, however, are more prone to unintentional chemical sensitization than silver bromide, and it is uncertain to what extent some chemical sen-... 

Surface image is formed predominantly in monodisperse, fine-grain emulsions prepared by the double-jet method. 

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