Moderately Concentrated Emulsions

In this case, account must be taken of the hydrodynamic interaction between the droplets, which reduces the Stokes velocity to a value v given, by the following expression [23]  

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Das et al. [46] have studied moderately concentrated emulsions (0.7 < < > < 0.9), from both a theoretical and an experimental standpoint. Both polydisperse and distorted monodisperse systems were considered for the former, it is possible to achieve a value of 0.89 for with undistorted spheres in a tridisperse (i.e. three sphere sizes) packing. 

X10" ms" for 10 pm droplets and 4.4 x 0 ms for 1 pm droplets. This means that in a 0.1 m container creaming or sedimentation of the 10 pm droplets is complete in 0.6 hour and for the 1 pm droplets this takes 60 hours. For moderately concentrated emulsions (0.2 < cj) < 0.1) one has to take into account the hydrodynamic interaction between the droplets, which reduces the Stokes velocity to a value v given by the following expression [97] ... 

Nonionic emulsifying wax is used as an emulsifying agent in the production of oil-in-water emulsions that are unaffected by moderate concentrations of electrolytes and are stable over a wide pH range. The concentration of wax used alters the consistency of a product owing to its self-bodying action at concentrations up to about 5% a product is pourable. 

With no salt present, moderately stable emulsions of the lower viscosity oil could be prepared at NaOH concentrations as low as 3.0 x 10 moles NaOH/gram oil. In the presence of 1.0% NaCl in the water, emulsions with NaOH contents above 5.0 x 10 3 were less stable than those with lower NaOH contents. In general average particle diameters decreased as NaOH concentration increased, with slightly lower particle sizes when<1.0% NaCl was present. Viscosities of the fresh emulsions were lowest at the lowest NaOH contents with or without salt. 

We have compared these theoretical predictions of the low-frequency modulus to experimental measurements on compressed emulsions and concentrated dispersions of microgels [121]. The emulsions were dispersions of silicone oil (viscosity 0.5 Pas) in water stabilized by the nonionic surfactant Triton X-100 [102, 121]. The excess surfactant was carefully eliminated by successive washing operations to avoid attractive depletion interactions. The size distribution of the droplets was moderately polydisperse with a mean droplet diameter of 2pin. The interfacial energy F between oil and water was 4mJ/m. The contact modulus for these emulsions was thus F 35 kPa. The volume fraction of the dispersed phase was easily obtained from weight measurements before and after water evaporation. Concentrated emulsions have a plateau modulus that extends to the lowest accessible frequencies, from which the low-frequency modulus Gq was obtained. Figure 11 shows the variations of Gq/E"" with 0 measured for the emulsions against the values calculated in the... 

It is important to note that die surprising validity of the dilute ECAH theory for moderately concentrated systems has only been demonstrated in systems where the fliennal losses were dominant, such as emulsions and latex systems. In contrast, a solid rutile dispersion exhibits nonlinearity of the attentuation above 10% by volume (Fig. 2). 

For measurements in emulsions, alkaline solutions, and solutions with only moderate concentrations of oxidizing or reducing agents, the weU-known quinhydrone electrode was further developed as solid composite electrode. 

Wax BP, Cetomacrogol Emulsifying Wax BP and Cetrimide Emulsifying Wax (BP) are ready prepared mixtures for extemporaneous use. When these or similar mixtures are used the resultant emulsions are mobile at low emulsifier concentrations and semi-solid at moderate concentrations (about 10% or less of the total weight of the emulsion). The process whereby the surfactant mixture imparts the semi-solid characteristics over a period of time has been termed self-bodying [92-94], the essential feature of which is the introduction of a significant elastic... 

Diesel-like products (jet fuel, diesel. No. 2 fuel oil, kerosene) are moderately volatile products that can evaporate with no residue. They have a low-to-moderate viscosity, spread rapidly into thin slicks, and form stable emulsions. They have a moderate-to-high (usually, high) toxicity to biota, and the specific toxicity is often related to type and concentration of aromatic compounds. They have the ability to penetrate substrate, but fresh (unoxidized) spills are nonadhesive. 

When the minimum against temperature of the interfacial tension between the two phases separated by a planar surface has a positive value (Fig. 3), their mixing will lead to an emulsion whose stability depends upon the magnitude of the surface excess. When the surfactant is sufficiently hydrophilic, it will be mostly distributed in water at low temperatures, and the surface excess will be small because of the high compatibility of the surfactant with the water phase. At high temperatures, the surfactant will be mostly distributed in the oil phase and the surface excess will be small because of the high compatibility between the surfactant and oil. At the moderate temperature T0 at which the concentrations in the two phases become equal, the surface excess is again small. 

Small, D. S., Acheampong, A., Reis, B., Stern, K., Stewart, W., Berdy, G., Epstein, R., Foerster, R., Forstot, L., and Tang-Liu, D. D.-S. (2002), Blood concentrations of cyclosporin A during long-term treatment with cyclosporin A ophthalmic emulsions in patients with moderate to severe dry eye disease, J. Ocul. Pharmacol. Then, 18, 411 118. 

An approach similar to that taken by Nomura and Harada was used by Samer to quantify the effects of droplet nucleation on emulsion polymerization kinetics in a CSTR. In their simplified analysis, it was assumed that radical capture by particles and droplets is proportional to the ratio of particle and droplet diameters. This assumption is reliable at low to moderate residence times, when polymer particles still closely resemble monomer droplets with respect to composition and surface characteristics. For predominant droplet nucleation, the maximum particle generation is limited by the concentration of monomer droplets in the feed. In Fig. 11 the steady state particle generation is given as a function of the residence time and temperature. Nucleation efficiency is defined as the number of particles divided by the number of droplets in the... 

SmaR DSjAcheampong A, Reis B, et al. Blood concentrations of cyclosporinA during long-term treatment with cyclosporinA ophthalmic emulsions in patients with moderate to severe dry eye disease. J Ocul Pharmacol Ther 2002 18 411-418. 

The side effects observed in the clinic with the early 100% and 90% w/v concentrated PFOB formula-tions and with Oxyfluor consisted of early effects, during or shortly after infusion, including headache and occasional lower backache, and delayed effects (2-12 h), referred to as flu-like symptoms e.g., fever, occasional chills and nausea.These reactions, generally categorized as mild, were transient and fully reversible within 4-12 h. A transient, moderate drop (about 15%) in platelet count was seen about 3 days after dosing. Similar effects have been documented for parenteral fat emulsions and liposomes, indicating that these effects were likely related to the particulate nature of the emulsion. 

Emulsions were prepared with the Shell crude and distilled water with sodium hydroxide concentrations varying from 1.0 x 10 to 8.0 x 10 moles NaOH/gram oil. The emulsions were very stable and no separation into two phases occurred when NaOH concentration was above 4.0 x 10 At 4.0 x 10 J and lower NaOH concentrations, some separation occurred after one or two days but even at 3.0 x 10 moderate stability was observed. Microscopic examination showed that the top layer contained a high fraction of oil with large particle sizes predominating and the bottom layer contained a high fraction of water with the small particle size oil droplets predominating. 

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