Emulsion breakage

Changes in the natures of individual phases of or phase separation within a formulation are reasons to discontinue use of a product. Phase separation may result from emulsion breakage, clearly an acute instability. More often it appears more subtly as bleeding—the formation of visible droplets of an emulsion s internal phase in the continuum of the semisolid. This problem is the result of slow rearrangement and contraction of internal structure. Eventually, here and there, globules of what is often clear liquid internal phase are squeezed out of the matrix. Warm storage temperatures can induce or accelerate structural crenulation such as this thus,... 

However, these systems are disadvantaged by emulsion swelling, emulsion breakage, lack of stability, and the fact that modeling tends to be complicated and tedious. Despite these disadvantages ELM systems have found applications in numerous simations such as the removal of metal ions, acids and bases from wastewater streams, and the recovery of biochemical products. 

Krishna, R., Goswami, A.N. and Sharma, A. (1987). Effect of emulsion breakage on selectivity in the separation of hydrocarbon mixtures using aqueous surfactant membranes. J. Membr. Sci., 34, 141-5. 

Emulsion swelling can also adversely affect ELM performance. Some degree of swelling is inevitable in the ELM process. Swelling is only a problem if it unacceptably reduces the driving force for the selenium extraction, unacceptably dilutes the internal-phase selenium concentration, creates handling problems, or leads to emulsion breakage. 

Beside the RDE extraction performances, their stability represents a crucial point that needs to be elucidated. While long-term emulsion stability should be ensured for the therapeutic applications, only short-term stability has to be achieved for environmental applications. For the later applications an emulsion breakage (splitting or coalescence) step is required in the process in order to separate the toxic-loaded emulsion into a toxic-concentrated aqueous solution, which is then valorized and the free oily phase is recycled in the emulsification step. These opposite requirements need more extensive parametric study to determine any delicate compromises. 

Figure 7.9 The PIT concept. As the temperature increases, the macroemulsion type changes from O/Wover the Winsor I region to W/O over the Winsor II region, through the emulsion breakage at the balanced point...

Over the Winsor II region, the W/O emulsion breakage was analyzed by the conventional Arrhenius plot ... 

A faster emulsion breakage at the lowest surfactant concentration (4%) is probably due to the fact that the surfactant monolayer is no longer saturated. The... 

The C12E5 concentration in oil is equal to 4% (squares), 15% (circles), 20% (triangles), and 30% (diamonds). Once the surfactant concentration exceeds the critical micelle concentration (ca 4% at 80 the emulsion breakage is consistent with the Arrhenius effect with an activation energy 42 49 kjT, which is fairly independent of the surfactant concentration. At 4% surfactant concentration the monolayer is not saturated and its bending modulus is very low, which produces a steeper stability decay... 

An important parameter that has to be considered during desulfurization as well as for subsequent biocatalyst separation and recycle is the impact of the oil phase on the biocatalyst activity and half-life. Additionally, the effect of the biocatalyst on forma-tion/breakage of the oil-water emulsions is also important. The latter will be discussed in Section 2.3.3. It becomes important for lower boiling feedstocks such as gasoline, which offers the most toxic solvent environment for the biodesulfurization catalyst. The effect of solvents on biocatalysts has been investigated in very few reports. A study by the Monot group reported effect of two solvents on several Rhodococcus strains [254], The strains contacted with the solvents and their desulfurization activity, growth, and... 

Liquid formulations account for about 30% of products in the UK market and, because they are easy to swallow, are favoured for paediatric and geriatric use. An aqueous solution is the simplest formulation to produce, but more complex suspensions or emulsion systems will be required if the drug is poorly soluble. Liquid formulations can be administered by all routes and are probably the most versatile systems. Liquids are, however, bulky, difficult to transport and container breakage can result in catastrophic loss. 

General model for physical transport of solute disregarding any chemical reaction effects. The model accounted for the continuous phase resistance and the interfacial resistance and permeation through a composite emulsion globule. It also quantified the loss in extraction efficiencies by leakage due to membrane breakage. 

Model accounted for external phase mass transfer resistance, the interfacial reaction resistance, diffusion within the emulsion globule as well as leakage of the internal phase due to membrane breakage. 

The disadvantages of sweUing are dilution of the separated product in the internal phase, an increase in membrane mpture/breakage, and an increase in agitation power required to disperse the emulsion [121]. 

Different methods [120] such as volume variation, internal phase droplet size variation, viscosity variation, density variation, tracer method, Karl-Fischer method, and electrical conductivity have been employed in the measurement of emulsion swelling. The data obtained tends to be as varied as the methods used [120]. One major drawback is that none of the above methods is capable of determining both emulsion swelling and membrane breakage in the same experiment. Further, osmotic swelling cannot be differentiated from entrainment swelling. 

Emulsions are characterized in terms of dispersed / continuous phase, phase volume ratio, droplet size distribution, viscosity, and stability. The dispersed phase is present in the form of microscopic droplets which are surrounded by the continuous phase both water-in-oil (w/o) and oil-inwater (o/w) emulsions can be formed. The typical size range for dispersed droplets which are classified as emulsions is from 0.25 to 25 p (6). Particles larger than 25 p indicate incomplete emulsification and/or impending breakage of the emulsion. Phase volume ratio is the volume fraction of the emulsion occupied by the internal (dispersed) phase, expressed as a percent or decimal number. Emulsion viscosity is determined by the viscosity of the continuous phase (solvent and surfactants), the phase volume ratio, and the particle size (6). Stroeve and Varanasi (7) have shown that emulsion viscosity is a critical factor in LM stability. Stability of... 

However, the PEO chain can become dehydrated at high temperatures (due to breakage of hydrogen bonds), which reduces the effective steric stabihsation. Thus, emulsion polymerisation should be carried out at temperatures well below the theta (0)-temperature of PEO. 

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