Hydrophilic particulate solids

Aid in the uniform dispersion of additives. Make powdered solids (e.g. particulate fillers with high energy and hydrophilic surface) more compatible with polymers by coating their surfaces with an adsorbed layer of surfactant in the form of a dispersant. Surface coating reduces the surface energy of fillers, reduces polymer/filler interaction and assists dispersion. Filler coatings increase compound cost. Fatty acids, metal soaps, waxes and fatty alcohols are used as dispersants commonly in concentrations from 2 to 5 wt %. 

Nature of the soil Oily soil or particulate soil, hydrophobic or hydrophilic, liquid or solid... 

Anionic and nonionic surfactants can reduce the work required to remove solid particles. This is because these surfactants adsorb to hair or hydrophobic soils with their hydrophobic tails in contact with the hydrophobic surfaces and their hydrophilic heads oriented toward the bulk solution. This has the effect of reducing ypw and ypw and, thus, Wa. Even more importandy, anionic surfactants remove particulates as a result of the increase of negative potentials on soil and hair upon anionic adsorption to these surfaces. This increases mutual repulsion between particulate and fiber, thus facilitating soil removal. 

The basic interfacial process in flotation is selective hydrophobization (or lepophiliza-tion) and hydrophilization of particulate matter. The role of the solution chemistry is very important in flotation as it is determined by the dissolution behavior of mineral particles in the aqueous solution (pulp) and subsequent dissociation, hydrolysis and precipitation of the soluble species the dissolution, association, dispersion and emulsion behavior of various flotation reagents in the pulp and interactions among reagents with both soluble and surface species of minerals. The efficiency of flotation and separation of mineral particles and consumption of reagents are thus controlled by the solution chemistry of the pulp. As other processes such as oil displacement are also governed by such interactions and in turn by the wettability of the solid surface, the study of solution chemistry of surfactant/mineral/additive systems become very important for the development of many technologies. 

This alteration in the hydrophobic characteristics of a known polar substance such as Cortisol is also extended to other molecules. It was observed that a polysaccharide powder saturated with a lipid shows a linear displacement of the lipid by the addition of water since the polysaccharide has a higher water affinity than it has lipid affinity. However, if a hyper-molar urea solution is used to displace the lipid, a distinct change in the hydrophilic/lipophobic characteristics of the polysaccharide takes place. Figure 19.2 shows the linear displacement of lipid from a saturated polysaccharide particle by water. Displacement continues up to 90% whereas in the case of 9.5 molar urea solution displacement of lipid ceases at approximately 45%. This displacement curve for urea solution is quoted here in millilitres of water corrected for the volume occupied by urea. It can, therefore, be seen that the effect of urea on the polysaccharide particle is virtually to form an ambiphilic particle from a solid particulate material. 

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