Emulsification temperature-controlled

In the laboratory, very reproducible W/0 emulsions of monodispersed size distributions can be prepared when all the variables for emulsification are controlled. The variables for a beneh laboratory study are emul-sifier type and concentration, energy of mixing, time of mixing, method of mixing, volume fraetions of oil and water phases, type and viseosity of oil, quality of water, and temperature. The mixtiue is blended in specific vessels, usually with rest intervals to eontrol the rigidity of the film. The conditions are reprodueed from batch to batch. In real production this is not often the case. The immiseible phases are subject to variable high shear for 2-8 min in offshore production and 40-50 min in the oil sands extraetion process. Emulsion size distributions therefore vary with different systems. 

Figure 6.17 SEM photographs and size distribution of a W/O solid lipid carrier with a mean size of 8.4zyxonetwothreexyzm for oral administration of anticancer drng irinotecan hydrochloride (CPT-11). The carrier was prepared by a temperature-controlled emulsification at 30kPa using SPG membrane with a mean pore size of 11.2zyxonetwothreexyzm, followed by cooling down and filtration of the solidified W/O/W emulsion (Shimizu et al., 2002a).

In all the experimental studies discussed below, the macroemulsion stability was characterized by the time for the resolution of one half of the emulsified disperse phase Ti/2, similar to how it had been done before by Salager et a/. All the macroemulsions contained 50 vol% of disperse phase and were prepared by handshaking in a jacketed beaker under careful temperature control. The emulsification was quite easy to perform because of the very low interfacial tensions in the system. The experimental reproducibility in r,/2 values was fairly good (within 20%) in the Winsor III experiment, provided that the temperature was controlled to within 0.01 °C. In other words, the way in which the macroemulsions were prepared... 

This observation needs to be compared to the few literature reports on the underlying factors that control the preparation of the albumin particles by the emulsification process. For example, it has been widely reported that parameters such as the variability in stirring rates and temperature had a significant influence on the size of the resulting beads and it has been concluded that the main process variables were controlled by the oil phase of the emulsion. 

The resistance to fluid flow is a measure of the physical structure of the foam. In order to control the flow through a foam, ceU size, degree of reticulation, density, and other physical factors must be controlled. The control of these physical factors, however, is achieved through the chemistry and the process by which the foam is made. The strength of the bulk polymer is measured by the tensile test described above, but it is clear that the tensile strengths of the individual bars and struts that form the boundaries of an individual cell determine, in part, the qualities of the cells that develop. A highly branched or cross-linked polymer molecule will possess certain tensile and elongation properties that define the cells. The process is also a critical part of the fluid flow formula, mostly due to kinetic factors. As discussed above, the addition of a polyol and/or water to a prepolymer initiates reactions that produce CO2 and cause a mass to polymerize. The juxtaposition of these two reactions defines the quality of the foam produced. Temperature is the primary factor that controls these reactions. Another factor is the emulsification of the prepolymer or isocyanate phase with the polyol or water. 

All hydrophilics are currently processed by the prepolymer method. The emulsification of the prepolymer and water are the primary determinants of cell size. The water also serves as a heat sink to moderate the temperature of the reaction. By adjusting the temperatures of the prepolymer and the water, one can control the kinetics described above. The mass of the water limits the destructive exotherm. 

Other emulsification protocols are based on a transient phenomenon, in which a dominant role is played by an unsteady mechanism, e.g., rrutss transfer through interface, which is not easy to ascertain or control. Often the nonequilib-riuin is driven by a continuously programmed change in a single variable such as temperature, amount or type of surfactant, watcr-to-oil ratio, etc., so that a phase behavior fionlicr is crossed and some event such as an emulsion inversion... 

Desmaison et al. conducted studies on Arabian crudes and noted the emulsion formation was correlated with two factors - photo-oxidation exposure and amount of asphaltenes (16). The photo-oxidation was found to occur on the aromatic fractions of the oil. Asphaltenes were found to become structured with time and this was associated with emulsion formation. Miyahara reported that the stability of emulsions was primarily controlled by the composition of the oil, specifically that which resided in flie hexane-insoluble fraction of the oil, but he did not define what fliis content was (17). Miyahara also reported that salt and freshwater emulsions showed relatively similar stabilities, alfliough in one case the salt-water emulsion appeared to be more stable. Payne and Phillips reviewed the subject in detail and reported on their on experiments of emulsification wifli Alaskan cmdes in fire presence and absence of ice (18). Their studies showed fliat emulsion formation could occiff in an ice field, thus indicating that fliere was sufficient energy in this environment and that the process could occur at relatively low temperatures. 

Art and magic aside, there are three principal methods of emulsion preparation which are most often employed. A fairly comprehensive coverage of those methods is presented in the work by Becher et al., cited in the Bibliography. The three methods most often employed include (1) physical emulsification by drop rupture, (2) emulsification by phase inversion, and (3) spontaneous emulsification. The latter two methods may be described as chemically based processes in that the nature of the final emulsion will be controlled primarily by the chemical makeup of the system (the chemical nature of additives, the ratios of the two phases, temperature, etc.), while in the first it will depend more on the mechanical nature of the process (e.g., amount and form of energy input.), as well as the rheological and chemical properties of the components. Other possibilities exist (see Table 11.1) however, most are of limited practical importance. 

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