Multiple emulsions viscosity

Most emulsions, unless very dilute, display hoth plastic and pseudoplastic flow behaviour rather than simple Newtonian flow. The flow properties of fluid emulsions should have little influence on their biological behaviour, although the rheological characteristics of semisolid emulsions may affect their performance. The pourability, spreadability and syringeability of an emulsion will, however, be directly determined by its rheological properties. The high viscosity of w/o emulsions leads to problems with intramuscular administration of injectable formulations. Conversion to a multiple emulsion (w/o/w), in which the external oil phase is replaced by an aqueous phase, leads to a dramatic decrease in viscosity and consequent improved ease of injection. 

The chapter has dealt with the stability and stabilisation of colloidal systems and covered topics such as their formation and aggregation. If the particle size of a colloidal particle determines its properties (such as viscosity or fate in the body), then maintenance of that particle size throughout the lifetime of the product is important. The emphasis in the section on stability is understandable. Various forms of emulsions, microemulsions and multiple emulsions have also been discussed, while other chapters deal with other important colloidal systems, such as protein and polymer micro- and nanospheres and phospholipid and surfactant vesicles. 

Norpar 13 were found to be too unstable for practical use. However, multiple emulsions of liquid paraffin (222 cP) prepared by Panchal et al (25) were less stable than those prepared with kerosene (viscosity 15 cPj, stability being measured by loss of internal aqueous phase. 

Flocculation of the multiple emulsion drops that would be accompanied by an increase in the viscosity of the system. 

It should be noted that type A multiple emulsions are not encountered much in practice, while type C is difficult to prepare as a large number of small water internal droplets (which are produced in the primary emulsification process) results in a large increase in viscosity. Thus, the most common multiple emulsions used in practice are those represented by type B. 

Another important use of the PHS-PEO-PHS block copolymer is the formation of a viscoelastic film around water droplets [11, 12] this results from the dense packing of the molecule at the W/O interface, which leads to an appreciable interfacial viscosity. The viscoelastic film prevents transport of water from the internal water droplets in the multiple emulsion drop to the external aqueous medium, and this ensures the long-term physical stability of the multiple emulsion when using polymeric surfactants. The viscoelastic film can also reduce the transport of any a.i. in the internal water droplets to the external phase. This is desirable in many cases when protection of the ingredient in the internal aqueous droplets is required and release is provided on application of the multiple emulsion. 

The structure of adsorption layers is of great importance during preparation of food foams and emulsions. These problems have been studied in [144] for protein adsorption at the liquid/gas interfaces and in [145] for liquid/liquid interfaces. Due attention is also paid to the interaction of typical emulsifiers and proteins during preparation of food emulsions [146 - 147]. Addition of an oil-soluble emulsifier to proteins during preparation of w/o emulsions [146] increased the emulsification rate, but at high concentrations decreased it due to the increase in oil viscosity. In this case, the emulsifier displaced (3-casein from the surface easier than P-lactoglobulin. However, there was no complete displacement into the aqueous phase since multiple emulsions were formed, as mentioned above [142 -143]. Hence, the ehoice of the surfactant/protein ratio is important. 

Figure 2 indicates the different types of emulsions. Simple emulsions are labeled as oil-in-water (0/W) when they exhibit oil drops dispersed in an aqueous phase, or water-in-oil (W/O) if the opposite occurs, while multiple or double emulsions are symbolized either by W,/0/Wi or Oi/W/O . Wi (respectively 0 ) and W2 (respectively O2) indicate the most internal phase and the most external one. Note that phases with subscript I and 2 may be identical or different. If they are not the same a likely difference in chemical potential may drive a mass transfer process, a phenomenon that is advantageously harnessed for controlled-release applications. Bieniulsions are emulsions containing two different internal phase droplets, either of the same nature (but different size) or of different nature (whatever the size). The first kind of biemulsion is used to control some property, as, for example, emulsion viscosity, whereas the second may be used to produce controlled chemical reaction or mass transfer between the two internal phases. 

Ketamine leaves the blood very rapidly to be distributed into the tissues. The recommended dosage of intravenous Ketamine is 2.5—20 mg/kg. The objective of the study was to test the concept that a multiple emulsion could be formulated which has high porosity and lower viscosity at 37°C consistent with its intended use for sustained drug release and to prolong the half-life of the anesthesia. The results showed that 8.2% of the Ketamine was released (100 mg/ml in the inner phase) after 10 min, 67.0% at 30 min, and 95.5% at 60 min from the Ketamine/OAV multiple emulsion in a well-controlled manner (Figs. 23 and 24). 

Stroeve and Varanasi (103) examined also the break up of the multiple-emulsion globules in a simple shear flow and concluded from the critical Weber number [(we), j.] (Figs. 35 and 36) that the multiple emulsion exhibits behavior that is similar to that of simple emulsions. From Fig. 35 one can see at least qualitatively, from the evolution of as a function ofp (the viscosity ratio between the... 

Figure 35 The critical Weber number for simple and multiple emulsions disruption as a function of the viscosity ratio dispersed to continuous phase. (From Ref 103.)...

Multiple emulsions, or subinclusions, were observed in many of the PS/P(MMA-S) specimens for example, they are clearly visible in Figures 6, 8, 9, 10, 16, 17, and 30, and a spectacular example is illustrated in Figure 39. This phenomenon can be understood in terms of the PS/P(MMA-S) phase diagram and the viscosity of the polymerizing system, and we conclude our report with this discussion. 

Paheme emulsion model failed to describe the dynamic modulus of the PP/EPDM blends after radiation, because the viscosity ratio increased significantly and the rubber phase changed from deformed droplets to hard domains after radiation (Cao et al. 2007). Intercoimections among inclusions of the dispersed phase (Shi et al. 2006) and the existence of multiple emulsion (emulsion-in-emulsion) structure exhibiting different relaxation domains in compatibilized systems are other factors contributing to the failure of Palieme s model (Friedrich and Antonov 2007 Pal 2007). 

G. T. Vladisavljevic, M. Shimizu, T. Nakashima, Production of multiple emulsions for drug delivery systems by repeated SPG membrane homogenization Influence of mean pore size, interfacial tension and continuous phase viscosity, J. Membr. Sci. 2006, 284, 373. 

Whether or not an emulsion is stabilized by solids will determine the nature of the demulsifier that will be most effective. In addition, the presence of multiple emulsions (water-in-oil-in-water-in-oU, etc.) is often symptomatic of demulsifier overtreatment. Figure 5 shows an oUfield emulsion formed when a free water knockout vessel was contaminated with viscosity reducers from an earlier well fracture. Similar multiple emulsions can result from overtreatment of the produced fluid by demulsifiers in the process. 

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