Dispersants in aqueous systems

Such carbonyls may be further oxidized using potassium permanganate (KMnO and perchloric acid (HCIO4) to convert all of these groups into carboxylic acids. Once functionalized in this manner, the nanotubes can be fully dispersed in aqueous systems. Kordas et al. (2006) used these derivatives to print nanotube patterns on paper or polymer surfaces to create conductive patterns for potential use in electronic circuitry. The carboxylates also may be used as conjugation sites to link other ligands or proteins to the nanotube surface using a carbodiimide reaction as previously discussed (Section 1, this chapter Chapter 2, Section 1.11 Chapter 3, Section 1). 

Colloids are thermodynamically unstable conglomerates that form heterogeneous dispersions in aqueous systems. They tend to coagulate and precipitate, which means that the materials of which they are composed may be present both in the water column and in sediments. The coagulation and precipitation stages are generally considered irreversible, but forces in the environment can redisperse the particles. 

The sulfonated lignin products function primarily as dispersants in aqueous systems and help to form stable dispersions of a number of insoluble materials. For example, lignin dispersants find use in pigments, carbon black, gypsum, ceramics, coal slurry and water treatment systems to mention some of the more prominent applications. 

In plant and animal tissues the carotenoids are usually found associated with lipid fractions in noncovalent association with membranes and lipoproteins, and they accumulate, together with chlorophylls, in the chloroplasts of green leaves (16). They also occur as very fine dispersions in aqueous systems, such as orange juice. 

The most common types of colloidal dispersions in aqueous systems are... 

HERCULES 831 defoamer readily disperses in aqueous systems and develops its foam-control action rapidly. Thus, it can be used where little agitation is available to disperse the foam killer, or where it must be added adjacent to the point of foam control. Preferably, 831 defoamer should be added as received to the foaming system. However, for ease of metering, it can be dispersed with continuous agitation in aqueous systems prior to addition. 

For sub-micron metallic powders, precoating with gelatin aids dispersion in aqueous systems. Coating of commercial powders in order to stabilize them is widely used e.g. aluminum oxide coated titanium dioxide. In such cases the interfacial properties will be those of the coating rather than those of the bulk powder. 

Modified lecithins. Lecithins may be modified chemically, e.g., hydrogenation, hydroxylation, acetylation, and by enzymatic hydrolysis, to produce products with improved heat resistance, emulsifying properties, and increased dispersibility in aqueous systems (7, 58, 59). One of the more important products is hydroxylated lecithin, which is easily and quickly dispersed in water and, in many instances, has fat-emulsifying properties superior to the natural product. Hydroxylated lecithin is approved for food applications under Title 21 of the Code of Federal Regulations 172.814 (1998) (60). 

Method of manufacture all industrial processes for preparing carotenoids are based on P-ionone. This material can be obtained by total synthesis from acetone and acetylene via dehydrolinalol. The commercially available material is usually extended on a matrix such as acacia or maltodex-trin. These extended forms of beta-carotene are dispersible in aqueous systems. Beta-carotene is also available as micronized crystals suspended in an edible oil such as peanut oil. 

The original studies of hydrogenation of phospholipids dispersed in aqueous systems were performed using Wilkinson s catalyst introduced in a solvent vector of tetrahydrofuran [1, 9, 10], It was shown that complete hydrogenation of the dispersed lipid could be achieved under relatively mild conditions of temperature, hy-... 

Hydrogenation of unsaturated phospholipids dispersed in aqueous systems using a water-soluble homogeneous catalyst was first reported in 1978 [22], The catalyst was a sulfonated derivative of Wilkinson s catalyst which did not appear to affect the structure of bilayers with respect to their permeability barrier properties [23]. The catalyst was found to hydrogenate oil-in-water emulsions and two-phase oil/water systems without the need for organic co-solvents [24]. 

Supercritical CO2 extraction has been used to extract PC from deoiled soybean lecithin selectively (Teberikler el al. 2001). The effects of temperature, pressure and amount of ethanol on PC extraction were examined and optimum conditions described to yield a high-purity product. Soybean lecithins can be chemically altered to modify their emulsifying properties and to improve their dispersibility in aqueous systems. Phospholipids may be hydrolyzed by acid base or enzyme (phospholipase A) to achieve better hydrophilic and emulsification properties. Hydroxylation of lecithin improves its oil-in-water emulsification property and water dispersibility. Acetylation (of PE) creates improved fluid, emulsification, and water dispersion (List 1989). 

Hydrogenation of unsaturated phosphohpids dispersed in aqueous systems using a water-soluble homogeneous catalyst was first reported by Madden and Quinn [1]. 

Outstanding properties very soluble in most organic solvents and is dispersible in aqueous systems ... 

Stabilized, surface-treated micronized rutile. This has very good photochemical stability and dispersability in aqueous systems good for urea and melamine moulding compounds and rigid PVC. 

Untreated micronized anatase. This has very good brightness, bluish colour tone, high tinting strength, and good dispersability in aqueous systems. 

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