Emulsification-evaporation processes

In an early study by Lin et al., insulin-loaded polylactic acid (PLA) microcapsules were synthesized by an emulsification-solvent evaporation process originally reported by Beck et al. Several parameters in the synthesis process were modified with the intention of optimizing the insulin release profile. Such modifications included variations in types, concentrations, and viscosities of protective colloids used in the emulsification process. Polyvinyl alcohol (PVA), when used as the protective colloid in the fabrication process, was found to produce the PLA microparticles in reproducible quality. Further studies revealed that the concentration PVA directly affects the PLA particle size and the surface characteristics of the microcapsules. With higher concentrations of PVA, microparticles tended to be smaller and to have a smoother surface. When the release profiles of the microcapsules were stud-... 

J. Jaiswal, S. K. Gupta and J. Kreuter, (2004). Preparation of biodegradable cyclosporine nanoparticles by high-pressure emulsification-solvent evaporation process. J. Control Release, 96(1), 169-178. 

The porosity (ie, pore size and amount of pores) of microparticles is also an important characteristic to take into consideration when fabricating microparticles because it plays an essential role in controlling the release of payloads. The porosity and morphology of particles are usually determined by scanning electron microscopy (SEM). For the emulsification solvent extraction/evaporation method of fabrication, the rate of solvent extraction, which depends on the flow in the stirred vessel the droplet size the temperature and the dispersed phase hold-up in the 0/W emulsion have an effect on porosity [87]. The porosity usually increases with a decrease in solvent extraction rate. The porosity of microparticles results in initial burst release due to pore diffusion [78,88]. Mao et al. studied the influence of different W/O/W emulsification solvent extraction/evaporation process parameters on internal and external porosity of PLGA microparticles [78]. The surface morphology of the microparticles can be influenced by the type of polymer, internal aqueous phase voliune (Wi), volume of continuous phase (W2), polymer concentration, homogenization speed, and equipment used for the primary emulsion [78,79]. 

As mentioned, the most adopted bioresorbable polymers to synthesize NPs for medical and pharmaceutical applications are polyesters such as PLA, PGA, poly(lactic-co-glycolic acid) (PLG A), and PCL. However, such polymers are generally synthesized in bulk phase via ROP and obtained as solids. Therefore, for producing biodegradable polymeric NPs, physical processes are required that allow for obtaining a stable suspension starting from the dry polyesters. Several methods have been proposed to synthesize NPs by dispersing a preformed polymer, but the most widely adopted methods are emulsification-evaporation and nanoprecipitation (Fig. 12.3) [5,6]. 

FIGURE 14.6 Modification of magnetic latex particles via an emulsification and evaporation process. 

Other test media and techniques include post-emulsification penetrants, penetrants that form gels resistant to easy removal from entrapments, penetrants that concentrate dye constituents as their carrier Hquids evaporate during test processing, and penetrants that form strippable coatings in the developers. StiU other penetrant systems are formulated for use at abnormally low or high temperatures for special test appHcations. 

The primary processes determining the fate of crude oils and oil products after a spill are (1) dispersion, (2) dissolution, (3) emulsification, (4) evaporation, (5) leaching, (6) sedimentation, (7) spreading, and (8) wind. These processes are influenced by the spill characteristics, environmental conditions, and physicochemical properties of the material spilled. 

Certain oils tend to form water-in-oil emulsions (where water is incorporated into oil) or mousse as weathering occurs. This process is significant because, for example, the apparent volume of the oil may increase dramatically, and the emulsification will slow the other weathering processes, especially evaporation. Under certain conditions, these emulsions may separate and release relatively fresh oil. Most of this process occurs from about half a day to two days after the spill. 

One of the major drawbacks of liposomes is related to their preparation methods [3,4]. Liposomes for topical delivery are prepared by the same classic methods widely described in the literature for preparation of these vesicles. The majority of the liposome preparation methods are complicated multistep processes. These methods include hydration of a dry lipid film, emulsification, reverse phase evaporation, freeze thaw processes, and solvent injection. Liposome preparation is followed by homogenization and separation of unentrapped drug by centrifugation, gel filtration, or dialysis. These techniques suffer from one or more drawbacks such as the use of solvents (sometimes pharmaceutically unacceptable), an additional sizing process to control the size distribution of final products (sonication, extrusion), multiple-step entrapment procedure for preparing drug-containing liposomes, and the need for special equipment. 

The solvent diffusion/spontaneous emulsification process can create much smaller droplet sizes than the solvent evaporation method. In this case, the dispersed phase is composed of a water-immiscible solvent and a water-miscible solvent, which is emulsified into an aqueous solution. The diffusion of the water-miscible solvent causes turbulence and further breakup of the droplets in the emulsion. The removal of solvent can be conducted similarly to the solvent evaporation method. 

Scheme 6 Similar to the process in Scheme 5, where emulsification of the polymer/drug organic solution takes place forming an oil-in-water system. The alternative is the dissolution of the polymer and drag in an aqueous phase, which is added to an organic phase to form a water-in-oil emulsion. In both cases, the internal phase is then evaporated leaving the polymer-drag particles.

The processes included in weathering are evaporation, emulsification, natural dispersion, dissolution, photooxidation, sedimentation, adhesion to materials, interaction with mineral fines, biodegradation, and the formation of tar balls. These processes are listed in order of importance in terms of their effect on the percentage of total mass balance, i.e., the greatest loss from the slick in terms of percentage, and what is known about the process. 

The tendency toward Pu(IV) polymerization is of considerable practical importance in process operations involving plutonium solutions. Dilution of an acidic plutonium solution with water can result in polymerization in localized regions of low acidity, so plutonium solutions should be diluted instead vdth acid solutions. Polymerization can result from leaks of steam or water into plutonium solutions or by overheating during evaporation. Polymer formation can clog transfer lines, interfere with ion-exchange separations, cause emulsification in solvent extraction and excessive foaming in evaporation, and can result in localized accumulation of plutonium that may create a criticality hazard [CS]. 

Biogeochemical Transformation of Oil Compounds in Marine Water Various biogeochemical and physical-chemical processes act within hours of an oil spill on the sea surface to alter its composition and toxicity, most importantly evaporation, dissolution, photochemical oxidation, advection and dispersion, emulsification, and sedimentation (Figure 7). 

When crude oil or petroleum products are accidentally released to the environment, whether on water or land, they are immediately subject to a wide variety of changes in physical and chemical properties that in combination are termed weathering . The weathering processes include (1) evaporation, (2) emulsification, (3) natural dispersion, (4) dissolution, (5) microbial degradation,... 

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