Nonaqueous emulsions

Emulsions. Aerosol emulsions (qv) may be oil in water (o/w), such as shaving creams, or water in oil (w/o), such as air fresheners and pohshes. These aerosols consist of active ingredients, an aqueous or nonaqueous vehicle, a surfactant, and a propellant, and can be emitted as a foam or as a spray. 

Solvent Gleaning. Solvent cleaning employs the natural solubilizing properties of various nonaqueous solvents or blends of solvents. Either 100% solvents or aqueous emulsions of solvents can be used. AppHcation is typically by immersion, hand appHcation, or via a vapor degreaser machine. 

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. 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

A wellbore fluid has been developed that has a nonaqueous continuous liquid phase that exhibits an electrical conductivity increased by a factor of 10 to 10 compared with conventional invert emulsion. 0.2% to 10% by volume of carbon black particles and emulsifying surfactants are used as additives. Information from electrical logging tools, including measurement while drilling and logging while drilling, can be obtained [1563]. 

A water-continuous emulsion, suitable for use as an antifoam additive, contains 85% to 98% by weight of a fluorosilicone oil and 2% to 15% by weight of an aqueous surfactant solution [1722]. The additive is suitable for use in separation of crude oil that contains associated gas. The additive may be used in both aqueous and nonaqueous systems and allows fluorosilicone oils to be used without the need for environmentally damaging chlorofluorocarbons. 

Microbes were frequently found to synthesise surface-active molecules in order to mobilise hydrophobic organic substrates. These biosurfactants, which are either excreted by the producing organisms or remain bound to their cell surfaces, are composed of a hydrophilic part making them soluble in water and a lipophilic part making them accumulate at interfaces. With respect to their physical effects, one can distinguish two types of biosurfactants firstly, molecules that drastically reduce the surface and interfacial tensions of gas-liquid, liquid-liquid and liquid-solid systems, and, secondly, compounds that stabilise emulsions of nonaqueous phase liquids in water, often also referred to as bioemulsifiers. The former molecules are typically low-molar-mass... 

Nonadsorptive retention of contaminants can also be beneficial. For example, oil droplets in the subsurface are effective in developing a reactive layer or decreasing the permeability of a sandy porous medium. Coulibaly and Borden (2004) describe laboratory and field studies where edible oils were successfully injected into the subsurface, as part of an in-situ permeable reactive barrier. The oil used in the experiment was injected in the subsurface either as a nonaqueous phase liquid (NAPL) or as an oil-in-water emulsion. The oil-in-water emulsion can be distributed through sands without excessive pressure buildup, contrary to NAPL injection, which requires introduction to the subsurface by high pressure. 

A.T. Florence, T.K. Law, and T.L. Wateley Nonaqueous Foam Structures from Osmotically Swollen W/OAV Emulsion Droplets. J. Colloid Interface Sci. 107,584 (1982). 

PAA can be prepared using bulk polymerization, aqueous polymerization, nonaqueous polymerization, inverse phase emulsion and suspension polymerization. The precise structure of the resulting PAA chain is dependent upon many factors including the polymerization process and conditions. The tacticity of... 

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). 

Dispersion polymerization differs from emulsion polymerization in that the reaction mixture, consisting of monomer, initiator, and solvent (aqueous or nonaque-ous), is usually homogeneous. As polymerization proceeds, polymer separates out and the reaction continues in a heterogeneous manner. A polymeric surfactant of the block or graft type (referred to as protective colloid ) is added to stabilize the particles once formed. 

Recently, emulsions based on oligomethylsiloxane liquids have been widely used as antifoaming agents to suppress or prevent foam in aqueous, nonaqueous and low-aqueous solutions, and as separating lubricants in pressure molds for tyre production. They are also used in foundry work to manufacture rods and in the production of elastomers and plastics. 

As presented in Fig. 10.13, the effect of Triton X-100 at 0.25 CMC was remarkable. Mass transfer coefficients were 5-fold higher than those obtained in absence of surfactant. The dispersion of nonaqueous-phase, leading to an increase in contact area, and the facilitated transport of the pollutant, probably due to reduction of surface tension or interaction of the pollutant with single surfactant molecules, may explain this increase of the mass transfer coefficients at concentrations lower than CMC [ 131 ]. On the other hand, mass transfer coefficients increased slightly when the agitation rate was increased from 200 to 250 rpm, which was coincident with the formation of the emulsion. The effect of increasing to 300 rpm had little impact on the mass transfer coefficients. The value of kt a with Triton at 300 rpm was not determined due to an inefficient separation of both phases. Finally, silicone oil of 10 and 20 cSt led to similar results, while solvent with 50 cSt always led to lower mass transfer coefficients. 

Micro emulsions can be formulated with carbon dioxide in supercritical state instead of a hydrocarbon as nonaqueous solvent. Fluorinated surfactants are commonly used to prepare such microemulsions. Water-in-carbon dioxide microemulsions can be made and the droplet size has been found to be similar to the size of the droplets of water-in-hydrocarbon micro emulsions with similar composition [21]. Such a microemulsion was used for conversion of benzyl chloride to benzyl bromide using KBr as hydrophilic nucleophile. The yield was an order of magnitude higher in the carbon dioxide microemulsion than in a conventional microemulsion at similar conditions, a fact that has been ascribed to low interfacial viscosity [22]. The big advantage with these micro emulsions is the environmental friendliness and the ease of work-up associated with carbon dioxide as solvent. 

Prior to this discovery, in 1954 Silberberg and Kuhn (62) were first to study the polymer-in-polymer emulsion containing ethylcellulose and polystyrene in a nonaqueous solvent, benzene. The mechanisms of polymer emulsification, demixing, and phase reversal were studied. Wetzel and Hocks discovery would then equate the pressure-sensitive adhesive to a polymer-polymer emulsion instead of a polymer-polymer suspension. Since the interface is liquid-liquid, the adhesion then becomes one type of R-R adhesion (35, 36). According to our previous discussion, diffusion is not operative unless both resin and rubber have an identical solubility parameter. The major interfacial interaction is physical adsorption, which, in turn, determines adhesion. Our previous work on the wettability of elastomers (37, 38) can help predict adhesion results. Detailed studies on the function of tackifiers have been made by Wetzel and Alexander (69), and by Hock (20, 21), and therefore the subject requires no further elaboration. 

Similarly In the emulsion system the potentials are grouped around the oxidation potential of Hyamlne indicating a chemical oxidation of the compounds by the electrolytlcally oxidized %amlne. However, In the micelle system the oxidations are spread over a wide range of potentials Indicating direct electrochemical oxidation of the compounds. This Is very similar to the results obtained In nonaqueous solutions, once more showing the hydrophobic nature of the electrode interface. 

In another investigation by the author [2] a selected bis-oxathiazaphosphohne derivative, (I), was prepared and used as a free radical regulator in aqueous and nonaqueous emulsion polymerizations of styrene. 

---