And dispersal in water

Hoyt and Sepaniak have used capillary zone electrophoresis to determine procaine in pharmaceuticals as a cation of benzylpenicillin [148]. A benzylpenicillin potassium tablet (250 mg) was treated with 20 mL of a 0.2% phenol solution (the internal standard), and dispersed in water. The solution was diluted to 500 mL, and samples were introduced into the fused silica capillary tube (70 cm x 50 gm) by siphoning. With 10 mM Na2HP04-6mM Na2B407 buffer as the mobile phase, the samples were subjected to electrophoresis at 30 kV (25 to 30 pA), and the emerging analytes detected at 228 nm within 10 minutes. 

In the detergency process, fatty materials (i.e. dirt, often from human skin) are removed from surfaces, such as cloth fibres, and dispersed in water. It is the surfactants in a detergent which produce this effect. Adsorption of the surfactant both on the fibre (or surface) and on the grease itself increases the contact angle of the latter as illustrated in Figure 4.7. The grease or oil droplet is then easily detached by mechanical action and the surfactant adsorbed around the surface of the droplet stabilises it in solution. 

As another example, small microcapsules of ibuprofen were film coated with cellulose acetate phthalate and dispersed in water before administration [54], Plasma levels were as expected and did not differ from those of a conventional enteric-coated tablet. 

A water-dispersible granule formulation contains typically a toxicant (50%-95%, w/w), dispersant, binder, and diluent. This formulation, also known as dry flowable, is intended for application after disintegration and dispersion in water by conventional spraying equipment. WGs are easier to use than WPs, because they have low-dust properties (due to larger particles) and exhibit good flowability. 

After the homogenization process, a 2ml of TEOS (99.9%, Aldrich Chemical Co., USA) was added and mixed into the catalyst-included mixed solvents. As reaction time goes on after ftie TEOS addition, the hydrolysis and condensation reactions initiated, so that the transparent solution became white and white. The reaction rate highly depended on the reaction conditions such as the volume ratio of H2O to EtOH and the addition amount of NH3. The synftiesis temperature and time were room temperature and 4hrs, respectively. After the synthesis reaction had proceeded for 4 hours, the synthesized silica gel was washed with water three times by repeated centrifuging and dispersion in water, and then dried at 110°C for 72hrs. All the chemicals used in the present study were used without any furthermore purification. 

Though fats are insoluble in water, they can be broken down into minute droplets and dispersed in water. This is called emulsification. 

Takei and Shimizu evaporated gold on one side of temporarily immobilized latex spheres (Figure 34). Immersion of the spheres in a thiol solution results in the formation of a monolayer, and subsequent removal of the spheres from the substrate and dispersion in water gives particles as small as 100 nm in diameter functionalized from one side only. Such colloid suspensions might find a range of interesting applications501. 

The impossibility of diluting PMDI with water was solved by the introduction of emulsified PMDI, often called EMDI, which allows an even distribution of the adhesive during the gluing process. EMDI is a product of the reaction of PMDI with polyglycols. EMDI is manufactured under high pressure and dispersed in water. 

Figure 10. Titania nanoparticles modified with various catechol ligands as stabilizers in the dry state (a) and dispersed in water (b) and tetrahydrofuran (c). Reproduced with alterations from Ref. [78] copyright 2004 American Chemical Society.

Lefebure, S., Dubois, E., Cabuil, V, Neveu, S., Massart, R. Monodisperse magnetic nanoparticles preparation and dispersion in water and oils. J. Mater. Res. 13, 2975-2981 (1998)... 

Monoglycerides are completely soluble in fats and oils and dispersible in water under certain conditions. Distilled monoglycerides form mesomorphic phases in water depending on temperature, concentration, fatty acid chain length and degree of unsaturation. 

Bleached sulfite softwood cellulose pulp shear refining, cryocrushing and dispersion in water by a disintegrator Refining to increase the accessibility of the cell 5-30 nm in diameter... 

Polyurethane emulsions and dispersions in water may also be made by incorporating polar or hydrophilic groups as described in Chapter 9. They are fully reacted, containing urethane and urea groups, are of high molecular weight, and may contain cosolvent. The chemistry of these is complex and beyond the scope of this book. They are used for the same applications as the solution polymers, and as primers for a range of plastic surfaces. 

Hybrid (or composite) latexes (169) are essentially a combination of the artificial latex and emulsion polymerisation methods (68, 167). A water-insoluble species (such as polymer) may be dissolved in monomer and dispersed in water in the same marmer as the artificial latexes. However, rather than removing the monomeric solvent, it is polymerised in the droplets by the addition of initiator. The monomer-swollen polymer particles capture radicals and polymerise to form a polymeric blend or structured domains. In this maimer, polystyrene particles with styrene-butadiene mbber (SBR) inclusions have been prepared for impact modification applications. 

Micro-encapsulation involves stabilizing an emulsion by forming strong films around each droplet. This can be done with a combination of colloidal silica and gelatin as described by Brockett (685). Further study of the interaction of colloidal silica with cationic polymers or with cationic surfactants in oil or polymer emulsions and dispersions in water appears worthwhile, particularly from the standpoint of highly stabilized interfaces. 

Powders of CAR and KGM were mixed in various ratios and dispersed in water. 

Inverse emulsion polymerization is a term used for water in oil (monomer) dispersion polymerization as opposed to conventional emulsion polymerization where the monomer and polymer are largely insoluble and dispersed in water. The advantage is that high molecular weight polymers and copolymers of water-soluble monomers may be prepared without the attendant viscosity build mentioned earlier. The process chemistry is well established as indicated in the patent literature (230-233) but not widely used and likely to be less so as solvents are removed from processing. Spray drying is often used for polymer isolation (234). 

Water-reducible polyunsaturated acid substituted aqueous polyurethane dispersions are also being used (40). They can be made by reacting a diisocyanate with a polyol, monoglyceride of a drying oil, and dimethylolpropionic acid. The carboxylic acid groups are neutralized with a tertiary amine and dispersed in water. If aliphatic isocyanates are used, good color retention can be obtained. They are much more resistant to hydrolysis than conventional alkyd resins. Films also have excellent abrasion resistance. Cost can be reduced by blending in 10-20% of acrylic latex. 

Dispersions can also be made by solvent-free processes. For example, isophorone diisocyanate, polycaprolactone diol, polytetrahydrofiirandiol, and dimethylolpropionic acid are reacted with an NCO OH ratio of 1.6 1 to make an isocyanate-terminated prepolymer. The prepolymer is neutralized with triethy-lamine and dispersed in water. The prepolymer is then chain extended by reacting with hydrazine hydrate. 

In emulsion polymerization, the polymerization process (typically radical initiated) takes place in micellar reactors composed of monomer droplets stabilized by surfactant molecules and dispersed in water (Figure 9.1). A colloidally stable polymer dispersion or latex is formed in this reaction by a complex mechanism consisting of three distinct intervals termed Smith-Ewert intervals [ 3-5]. On addition of a dispersed phase soluble monomer to the surfactant/solvent system, the system contains monomer-swollen small surfactant micelles ( 10 nm in diameter) and large emulsion droplets of monomer. On the subsequent addition of a continuous phase soluble initiator, free radical spedes form which diffuse into the micelles. The monomer quickly polymerizes in the micelle and, as diffusion of monomer from the emulsion droplet to the micelle is rapid on the timescale of polymerization, the micelles contain both monomer and polymer. As the concentration of free monomer reduces to zero, the polymerization of the remaining monomer in the latex particles takes place, ending the reaction. Monodispersity is retained throughout the reaction to the final product as all polymerization takes place within the surfactant micelles [6, 7j. 

S Lefebure, E Dubois, V Cabuil, S Neveu, R Massart. Monodisperse magnetic nanoparticles Preparation and dispersion in water and oils. J Mater Res 1998 13 2975. 

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