Emulsified systems

Since poly(vinyl acetate) is usually used in an emulsion form, the emulsion polymerisation process is commonly used. In a typical system, approximately equal quantities of vinyl acetate and water are stirred together in the presence of a suitable colloid-emulsifier system, such as poly(vinyl alcohol) and sodium lauryl sulphate, and a water-soluble initiator such as potassium persulphate. 

In the production of crude oil, the greatest part of the crude oil occurs as a water-in-oil emulsion. The composition of the continuous phase depends on the water/oil ratio, the natural emulsifier systems contained in the oil, and the origin of the emulsion. The natural emulsifiers contained in crude oils have a complex chemical structure, so that, to overcome their effect, petroleum-emulsion demulsifiers must be selectively developed. As new oil fields are developed, and as the production conditions change at older fields, there is a constant need for demulsifiers that lead to a rapid separation into water and oil, as well as minimal-residual water and salt mixtures. 

M Gallarate, ME Carlotti, M Trotta, S Bovo. On the stability of ascorbic acid in emulsified systems for topical and cosmetic use. Int J Pharm 188(2) 233 241, 1999. 

HLB value of the oil phase. Further tests can then be carried out with different chemical types of agents around this effective HLB value in order to find the optimum emulsifying system. 

The environmental compatibility of silicone softeners is generally favourable [495,496]. The discussion here concerns only the silicone component of the formulation and not the supporting emulsifying system. For the most part this is nonionic, preferably based on linear ethoxylated fatty alcohols, although alkylphenol ethoxylates are still used in some countries [496]. The salient points regarding the environmental influence of silicones can be summarised as follows ... 

Lipid systems such as oils/emulsions/microemulsions/self-emulsifying systems in capsules... 

It is worth noting that the effect of temperature on ionic and polyethoxy-lated nonionic surfactants is just opposite. As temperature increases, the nonionics become more lipophilic whereas the ionics turn more hydrophilic. By mixing the two types of surfactants in a proper proportion, these effects could cancel each other out, and the mixture is said to be insensitive to temperature. This interesting feature of ionic-nonionic surfactant mixtures may be considered as a synergy, since it could be very important in practice. Analysis of this feature is not included here, because plenty of information may be found in the literature on applications of such mixtures to equihbrated and emulsified systems [10,71-74]. 

The concept of interfacial mesophases promoting spontaneous emulsification (21.22) can be applied to the Tagat TO - Miglyol 812 system, where stable liquid crystalline dispersion phases are adequate to promote the process of self-emulsification. The stability of the resulting emulsion systems can also be accounted for by liquid crystalline interface stabilisation (23.24). Phase separation of material as observed above 55f surfactant, in conjuction with the increased viscosities of such systems, will inhibit the dynamics of the self-emulsification process and hence the quality of self-emulsified systems declines when the surfactant concentration is increased above 55. ... 

Tabushi and coworkers106 have reported that dichlorocarbene reacts very readily with alcohols to give the corresponding chlorides. Dichlorocarbene was generated by using an emulsifying system the method involves treatment of the alcohol with chloroform in the presence of an aqueous solution of sodium hydroxide and a catalytic amount of benzyltriethylammonium chloride. 

Non-aqueous HIPEs have received even less attention indeed, to date, there have been only two publications dealing with this subject, to the authors knowledge [124,125]. These describe the preparation of highly concentrated emulsions of jet engine fuel in formamide, for use as safety fuels in military applications. The emulsifier system used was a blend of two nonionics, with an optimal HLB value of 12. 

Here, the source of the energy for these interactions is supposed to come from internal molecular forces such as the free energy of mixing that occurs during the violent mass transfer. One of the main characteristics of a spontaneously emulsifying system is that there is no requirement for the application of external energy. 

Key Concepts of Interfacial Properties in Food Chemistry CASE STUDY LIPID OXIDATION OF EMULSIONS The case of lipid oxidation in an emulsified system is a perfect example to illustrate the importance of interfacial properties in food chemistry. The goal of this case study is not to completely describe the very complex mechanisms of lipid oxidation in emulsions. Indeed, many investigators over the past years have focused on this research area. Instead, the key interfacial parameters that influence lipid oxidation in emulsions are emphasized. 

To overcome the fact that a single solvent rarely completely extracts all the potentially available components from a herb, multi-solvent extracts have been developed. In this process, initial extraction of the herb using a non-polar solvent is followed by extraction using a more polar solvent. The two extracts are then concentrated to remove the solvents. Finally, they are combined using a suitable emulsifier system to hold the two incompatible components together without separating. This will render the extract water soluble (or at the least miscible) without settling-out in the final product. 

Industrial uses of aerosols include aerosol propellants, anti foam sprays, fire extinguishers and paints. Herzka Pickthal (Ref 5) describe aerosol propellants, containers, valves, filling methods, lab procedures, emulsified systems, etc Refs 1)Webster s New Collegiate Dic-... 

Kim, J. Y., and Y. S. Ku. 2000. Enhanced absorption of indomethacin after oral or rectal administration of a self-emulsifying system containing indomethacin to rfertte.J. Pharm.194 81-89. 

Lipid-based formulations offer a large variety of optional systems. They can be made as solutions, suspensions, emulsions, self-emulsifying systems and microemulsions. Moreover, it is possible to form blends that are composed of several excipients they can be pure triglyceride (TG) oils or blends of different TG, diglyceride (DG) and monoglyceride (MG). In addition, different types of surfactants (lipophilic and hydrophilic) can be added, as well as hydrophilic co-solvents. Lack of enhanced absorption when one of the above key formulations is tested does not necessarily indicate the effectiveness of alternative lipid-based formulations, and their suitability has to be examined. 

Self-Emulsifying Systems Emulsion systems have the disadvantage of being physically unstable, and over time a separation between the oil and water phases of the emulsion will occur. The use of conventional emulsions is also less attractive due to poor precision of the taken dose and the relatively large volume that has to be administered. To overcome these limitations, self-emulsifying drug delivery systems (SEDDS) have been developed. The... 

D. Q. M. Craig, El. S. R. Lievens, K. G. Pitt, and D. E. Storey, An investigation into the physico-chemical properties of self-emulsifying systems using low frequency dielectric spectroscopy, surface tension measurements and particle size analysis, Int. J. Pharmaceut. 96 147-155 (1993). 

To recapitulate, thioridazine release from microspheres was enhanced when NaOH was added to the emulsion prior to the solvent evaporation step. This was observed for both poly(DL-lactide) and poly(L-lactide) and also for two emulsifier systems, sodium oleate and polyvinyl alcohol. It should be pointed out that NaOH is added only to the aqueous phase of the emulsion. It is not incorporated into the microspheres by this process. 

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