Dispersions emulsions

The successful employment of any insecticide depends on its proper formulation into a preparation that can be appHed for insect control with safety to the apphcator, animals, and plants. Insecticides are commonly formulated as dusts, water dispersions, emulsions, and solutions. The preparation and use of such formulations involves accessory agents such as dust carriers, solvents, emulsifiers, wetting and dispersing agents, stickers, and deodorants or masking agents (1). 

Acryhc and methacryhc nonaqueous dispersions (NADs) are primarily utilized by the coatings industry to avoid certain difficulties associated with aqueous dispersion (emulsion) polymers. Water as a suspension medium has numerous practical advantages, but also some inherent difficulties a high heat of evaporation, a low boiling point, and an evaporation rate that depends on the prevailing humidity. Nonaqueous dispersions alleviate these problems, but introduce others such as flammabihty, increased cost, odor, and toxicity. 

J. Bibette, 1991, (Depletion interactions and fractionated crystallization for poly-disperse emulsion purification), J. Colloid Interface Sci. 147, 474. 

Forster, Th., von Rybinski, W. and Wadle, A. (1995) Influence of microemulsion phases on the preparation of fine-disperse emulsions. Advances in Colloid and Interface Science, 58, 119-149. 

FIG. 14. Transmission electron micrograph of Voltaren Emulgel the interface hetween the continuous hydrogel and the dispersed emulsion droplets consists of multiple bilayers of hydrated surfactant molecules, bar 500 nm. From Miiller-Goymann, C., and Schutze, W., Mehrschichtige Phasengrenzen in Emulsionen, Dtsch. Apoth. Ztg., 130 561-562 (1990). 

Although S-sensitization decreases low intensity reciprocity failure it usually does not eliminate it. In our experiments with monodisperse fine-grain silver bromide emulsion, vacuum outgassing of the S-sensitized emulsion eliminated the LIRF, just as it did for the unsensitized emulsion. Moreover, the sensitivities of the two emulsions under vacuum were nearly the same. Whatever may be the role of S-sensitization in this emulsion, it became inconsequential for exposures made under vacuum. However, the degree of increase in sensitivity caused by S-sensitization of the fine grain emulsions for exposures in air is much smaller than can be achieved with coarse-grain poly-disperse emulsions. 

The sizes of the droplets in the initial emulsion significantly affect the size and properties of the microspheres (Table 6)36). As the mixing rate used to produce the emulsions is increased, the average size of the droplets decreases whereas the microsphere size increases. Very dispersed emulsions seem to be more likely to coalesce, thus yielding larger droplets and hence larger microspheres after the heat treatment. This method can produce spherical unicellular particles with diameters of200-400 pm, densities of 260-700 kg/m3, and space factors of up to 59% 35 36). 

The starting mass is a smelt, solution, dispersion, emulsion or sol. 

In this review we summarize and discuss the amphiphilic properties of polyoxyethylene (PEO) macromonomers and PEO graft copolymer molecules, the aggregation of amphiphilic PEO macromonomers into micelles, the effect of organized aggregation of macromonomers on the polymerization process, and the kinetics of radical polymerization and copolymerization of PEO macromonomer in disperse (dispersion, emulsion, miniemulsion, microemulsion, etc.) systems [1-5]. 

The radical polymerization in disperse systems may be divided into several types according to the nature of continuous phase and the polymerization loci the dispersion, emulsion, miniemulsion, microemulsion, suspension, etc. 

MicroLuidization is a process involving a high-pressure Luids processor that delivers unique product capabilities, including particle size reduction to nanosized particles for dispersions, emulsions, and liposomes. MicroLuidizer processors overcome limitations of conventional processing technologies... 

Most types of polymerizations can be performed in liquid and supercritical C02. The two major types of polymerizations, chain-growth and step-growth, have been demonstrated in C02. Reviews in the literature (Canelas and DeSimone, 1997b Kendall et al., 1999) have described numerous polymerizations in C02, many of which will not be discussed in this chapter. Since only amorphous or low-melting fluoropolymers and silicones show appreciable solubility at relatively mild temperatures and pressures (T< 100 °C, P<400 bar), only these two classes of polymers can be synthesized by a homogeneous polymerization in C02. All other types of polymers, including semicrystalline fluoropolymers and lipophilic or hydrophilic polymers, must be made by heterogeneous methods, such as precipitation, dispersion, emulsion, and suspension, since the polymers are insoluble in C02 (when T< 100 °C and P<400 bar). Some semicrystalline fluoropolymers and hydrocarbon polymers can be dissolved at more extreme temperatures and pressures and are discussed in Chapter 7 of this book. 

Different architectures, such as block copolymers, crosslinked microparticles, hyperbranched polymers and dendrimers, have emerged (Fig. 7.11). Crosslinked microparticles ( microgels ) can be described as polymer particles with sizes in the submicrometer range and with particular characteristics, such as permanent shape, surface area, and solubility. The use of dispersion/emulsion aqueous or nonaqueous copolymerizations of formulations containing adequate concentrations of multifunctional monomers is the most practical and controllable way of manufacturing micro-gel-based systems (Funke et al., 1998). The sizes of CMP prepared in this way vary between 50 and 300 nm. Functional groups are either distributed in the whole CMP or are grafted onto the surface (core-shell, CS particles). 

Because of its heterophase nature, emulsion polymerization is generally more complicated than simple solution polymerization in which monomers and polymers are soluble in a suitably chosen solvent. In emulsion polymerization the different relative solubilities of monomers in water and in the polymer particles lead to different reaction locales and to different particle structures. Another complicating factor is the need to achieve and maintain colloidal stability throughout the polymerization and subsequent handling of the dispersions. Emulsion polymers can properly be called products by process since the process details exert such a powerful effect on the properties of the particles and resultant films. Consequently, an emulsion polymer is far more than a product defined by a simple polymer composition. 

This book provides an introduction to the colloid and interface science of three of the most common types of colloidal dispersion emulsions, foams, and suspensions. The initial emphasis covers basic concepts important to the understanding of most kinds of colloidal dispersions, not just emulsions, foams, and suspensions, and is aimed at providing the necessary framework for understanding the applications. The treatment is integrated for each major physical property class the principles of colloid and interface science common to each dispersion type are presented first, followed as needed by separate treatments of features unique to emulsions, foams, or suspensions. The second half of the book provides examples of the applications of colloid science, again in the context of emulsions, foams, and suspensions, and includes attention to practical processes and problems in various industrial settings. 

Water-dispersing emulsion with active contents of 5-50% with varying lonogenicity. 

Colloid Mill Colloid mills are rotor-stator systems that can be used to reduce the particle size distribution of both liquid dispersions (emulsions) and solid dispersions (suspensions). The emulsion or suspension is pumped through a narrow gap that is formed by the rotating inner cone and the stationary outer cone. The width of the annulus can be adjusted by changing the relative position of the two cones. The principal size reduction in colloid mills is due to the high shear forces that are caused by the velocity difference between the rotor and the stator surfaces. To increase wall friction and reduce slip, surfaces are usually not smooth but are roughened or toothed, which, in turn, changes the flow conditions from laminar to turbulent, thereby increasing the shear forces in the annulus. 

Kremsec VJ. Modehng of dispersed-emulsion separation systems. Sep Purif Methods 1981 10 117-157. 

Kremsec VJ and Slattery JC. Analysis of batch, dispersed-emulsion, separation systems. AIChE J 1982 28 492-500. 

A dispersed emulsion droplet (electrostatically stabilized) can be thought of as a charged center with a pliable cover of compensating charge due to orientation of the water molecules (or counterions) around the droplet. When exposed to an electric field, the droplet will move according to the surface charge. 

Classical theories of emulsion stability focus on the manner in which the adsorbed emulsifier film influences the processes of flocculation and coalescence by modifying the forces between dispersed emulsion droplets. They do not consider the possibility of Ostwald ripening or creaming nor the influence that the emulsifier may have on continuous phase rheology. As two droplets approach one another, they experience strong van der Waals forces of attraction, which tend to pull them even closer together. The adsorbed emulsifier stabilizes the system by the introduction of additional repulsive forces (e.g., electrostatic or steric) that counteract the attractive van der Waals forces and prevent the close approach of droplets. Electrostatic effects are particularly important with ionic emulsifiers whereas steric effects dominate with non-ionic polymers and surfactants, and in w/o emulsions. The applications of colloid theory to emulsions stabilized by ionic and non-ionic surfactants have been reviewed as have more general aspects of the polymeric stabilization of dispersions. ... 

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