Dispersing powders surfactants

Structural formers (oxides, carbides, nitrides, salts of organic acids, fine-dispersed powders, surfactants) exert an effect on the permolecular structure formation and assist in yielding materials with a given microstructure. A number of powder Cl can be related to active structuring agents. In particular, impregnation of small amounts of fine-dispersed Cl (NDA, G-2, 5-PhTet) in the polymer film materials improves their strength and barrier properties (see Sect. 2.3). 

Just because a surfactant adsorbs on the surface of a ceramic powder does not mean that it will stabilize the dispersion. The adsorbed surfactant will certainly help prevent the reagglomeration of the ceramic powder, like any adsorbed species, but the colloid stability of the ceramic powder-surfactant dispersion must be considered separately. Colloid stability is the subject of Chapter 10 of this book. 

In practice, the development of an optimum preparation route for a coating dispersion, for example, consisting of oxide powder, surfactant, dispersant and... 

The adsorption from solutions on finely dispersed powders and porous adsorbents is used for the removal of dissolved toxic components, as well as for concentrating and entrapping valuable substances from dilute solutions. In agreement with the polarity equalization rule, surface active substances dissolved in aqueous medium can be removed by adsorption on non-polar adsorbents (such as activated carbon), or on adsorbents that are capable of chemisorbing the surfactant polar heads. In order to increase the effectiveness... 

Belgacem, M.N. Gandini, A. Inverse Gas Chromatography as a Tool to Characterize Dispersive and Acid-Base Properties of the Surface of Fibers and Powders— Surfactant Science Series—VoL 80 Pefferkom, E., Ed. Marcel Dekker, Inc. New York, 1999,41-124. 

Surfactant. A surface active agent a chemical which reduces the surface tension of a liquid, and so improves the wetting of a surface. They are useful in dispersing powders, when surfactants adsorbed on particle surfaces produce repulsive forces between the particles when the adsorbed layers overlap (steric hindrance.)... 

The adsorption at the S/L interface between finely dispersed powders and aqueous solutions is measured by the same principle as described earlier, that is, by a decrease in the concentration c in solution, which can be most simply measured by the increase in the surface tension at the air-liquid interface. However, this method lacks accuracy, once the surfactant concentration exceeds the critical micellization concentration. For more accurate determination of surfactant concentrations, spectroscopic or chromatographic-mass spectrometric methods can be used. A review of the methods used to determine the concentration of different surfactants can be found in [5]. 

Aqueous Dispersions. The dispersion is made by the polymerization process used to produce fine powders of different average particle sizes (58). The most common dispersion has an average particle size of about 0.2 p.m, probably the optimum particle size for most appHcations. The raw dispersion is stabilized with a nonionic or anionic surfactant and concentrated to 60—65 wt % soHds by electrodecantation, evaporation, or thermal concentration (59). The concentrated dispersion can be modified further with chemical additives. The fabrication characteristics of these dispersions depend on polymerization conditions and additives. 

All lnaphthalenesulfonic Acids. The aLkyLnaphthalenesulfonic acids can be made by sulfonation of aLkyLnaphthalenes, eg, with sulfuric acid at 160°C, or by alkylation of naphthalenesulfonic acids with alcohols or olefins. These products, as the acids or their sodium salts, are commercially important as textile auxiUaries, surfactants (qv), wetting agents, dispersants (qv), and emulsifying aids, eg, for dyes (qv), wettable powder pesticides, tars, clays (qv), and hydrotropes. 

The cost/performance factor of individual surfactants will always be considered in determining which surfactants are blended in a mixed active formulation. However, with the recent advent of compact powders and concentrated liquids, other factors, such as processing, density, powder flowability, water content, stabilization of additives, dispersibility in nonaqueous solvents, dispersion of builders, and liquid crystalline phase behavior, have become important in determining the selection of individual surfactants. 

Ether carboxylates are used not only in powdered detergents but in liquid laundry detergents for their hard water stability, lime soap dispersibility, and electrolyte stability they improve the suspension stability and rheology of the electrolyte builder [130,131]. Formulations based particularly on lauryl ether carboxylate + 4.5 EO combined with fatty acid salt and other anionic surfactants are described [132], sometimes in combination with quaternary compounds as softeners [133,163]. Ether carboxylates show improved cleaning properties as suds-controlling agents in formulations with ethoxylated alkylphenol or fatty alcohol, alkyl phosphate esters or alkoxylate phosphate esters, and water-soluble builders [134]. 

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 %. 

Finely divided solid particles that are wetted to some degree by both oil and water can also act as emulsifying agents. This results from the fact that they can form a particulate film around dispersed droplets, preventing coalescence. Powders that are wetted preferentially by water form O/W emulsions, whereas those more easily wetted by oil form W/O emulsions. The compounds most frequently used in pharmacy are colloidal clays, such as bentonite (aluminum silicate) and veegum (magnesium aluminum silicate). These compounds tend to be adsorbed at the interface and also increase the viscosity of the aqueous phase. They are frequently used in conjunction with a surfactant for external purposes, such as lotions or creams. 

A surfactant is a surface-active agent that is used to disperse a water-insoluble drug as a colloidal dispersion. Surfactants are used for wetting and to prevent crystal growth in a suspension. Surfactants are used quite extensively in parenteral suspensions for wetting powders and to provide acceptable syringability. They are also used in emulsions and for solubilizing steroids and fat-soluble vitamins. 

This method was first reported by Vanderhoff [82] for the preparation of artificial latexes. The polymer and drug are dissolved or dispersed in a volatile water-immiscible organic solvent, such as dichloromethane, chloroform, or ethyl acetate. This is emulsified in an aqueous continuous phase containing a surfactant, such as poly(vinylalcohol), to form nanodroplets. The organic solvent diffuses out of the nanodroplets into the aqueous phase and evaporates at the air/water interface, as illustrated in Figure 6. The solvent is removed under reduced pressure. The nanodroplets solidify and can be separated, washed, and dried to form a free-flowing powder. 

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