Emulsions classical method

J.L. Salager A 3rd Type of Emulsion Inversion Attained by Overlapping the Two Classical Methods Combined Inversion. In Proceedings of the 3rd Word Congress on Emulsions l-E-180, Lyon, Erance (2001). 

A second classical method for making capsules from emulsions is to form the shell polymer in situ using interfacial polymerization (Morgan and Kwolek 1959 Wittbecker and Morgan 1959). This method is similar to the nylon rope trick often used as a demonstration, where a solution of diacid chloride in organic solvent (such as adipoyl chloride in hexanes) is layered in a beaker with a diamine aqueous phase (such as 1,6-hexadiamine in water Friedli et al. 2005). Because the two monomers meet only at the interface of the two phases, the condensation polymerization to form the polyamide occurs only at the interface. 

An assessment of emulsion stability involves the determination of the time variation of some emulsion property such as those described in the physical characteristics section above. The classical methods are well described in Ref. [9]. Some newer approaches include the use of pulsed nuclear magnetic resonance or differential scanning calorimetry [294]. 

As a classical method for observation of isotherms, the silver halide crystals in a suspension (a melted gelatin "emulsion") can be centrifuged out, leaving the clear supernatant liquid available for quantitative spectroscopic analysis. 

Most of the derivatives shown in Figure 8 are solvent extractable at low pH, and thus one of the classical methods used for antibiotic purification becomes accessible to cephalosporin C. To be commercially feasible, solvents should be selective and only slightly miscible with water. Extraction efficiency should be sufficiently high that multiple extractions are not required, and ideally should be efficient at low ratios so as to effect a concentration of the desired component. Emulsions and insoluble solids are anathema to extraction. Using these criteria, extraction of most of the cephalosporin C derivatives at low pH are far from ideal since mostly non-selective solvents (such as n-butanol and ethyl acetate) usually work best several extractions seem to be required, and derivatized cephalosporin C broth upon acidification will frequently result in emulsion formation. However, some derivatives behave better than... 

Conventional liquid-liquid extraction for the determination of lindane has been used very frequently up to the present time. However, this classical method of sample preparation has disadvantages, e.g. emulsion formation, poor phase separation, high consumption of solvent, and the labor-intensive nature of the process and its unsuitability for automation. It was important to find ways of... 

Equation (2.26) leads to a solution for from available knowledge of the rate R, the concentration of monomer in the monomer-polymer particles [M], and the number of particles, N. This method has been applied to several monomers and has been especially useful in the case of the dienes, where the classical method of photoinitiation poses difficulties. Some of these results are shown in Table 2.4 in the form of the usual kinetic parameters. The results obtained for styrene by photoinitiation techniques are included for comparison. It can be seen that the agreement is remarkably good, considering the widely different experimental methods used. Recent studies of the emulsion polymerization of butadiene have shown that the rate constant for propagation is even higher than previously estimated (see Table 2.1) (Weerts et al., 1991). 

These constitute the classic methods for preparing colloidal emulsions from two immiscible liquids of water and oil types. They require the use of equipment capable of providing the mechanical energy necessary to divide up the material, and also a properly adapted surfactant system. The role of the latter is to ... 

Classical methods of emulsion polymerisation employ an aqueous phase containing water and surfactant plus initiator to which is added the monomers to be polymerised. Commercial polymerisations utilising acrylic monomers normally use a pre-emulsion technique in which the monomer mixture has been dispersed in the water phase with a surfactant. This pre-emulsion is added continuously during the course of the reaction to the water phase contaiiting further surfactant. 

Figure 6.4 The preparation of nanostructured materials in solution evolves from (a) the classic examples of suspension, dispersion, or emulsion polymerization, to the methods that include the covalent crosslinking of select domains within supramolecular polymer assemblies (b) core crosslinking of polymer micelles (c) shell crosslinking of polymer micelles (SCKs) (d) nanocages from core-eroded SCKs (e) shaved hollow nanospheres from outer shell/core-eroded vesicles.

Not all emulsions exhibit the classical milky opaqueness with which they are usually associated. A tremendous range of appearances is possible, depending upon the droplet sizes and the difference in refractive indices between the phases. An emulsion can be transparent if either the refractive index of each phase is the same, or alternatively, if the dispersed phase is made up of droplets that are sufficiently small compared with the wavelength of the illuminating light. Thus an O/W microemulsion of even a crude oil in water may be transparent. If the droplets are of the order of 1 pm diameter a dilute O/W emulsion will take on a somewhat milky-blue cast if the droplets are very much larger then the oil phase will become quite distinguishable and apparent. Physically the nature of the simple emulsion types can be determined by methods such as [95] ... 

Direct solvent extraction before or after acid or enzymatic digestion has almost superseded die classic protein precipitation methods. Due to die more sensitive detection methods of gas chromatography and mass spectrometry, much smaller amounts of tissue can be processed. Consequently, any emulsion problems that arise are more easily resolved than in the past when several hundred grams of liver and large volumes of solvent were required. 

Effective compatibilization of binary polymer blends by addition of a copolymer should reduce the interfacial tension coefficient. Often, it also alters the molecular structure of the interface (as measured by the scattering methods). The process is similar to the emulsification in the classical emulsions. The emulsifier effect on the droplet size follows generally the same behavior as the interfacial tension. This behavior is described by the emulsification curves (evolution of the particle s size with the emulsifier content) and characterizes the additives efficiency. The shape... 

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