Inorganics, solubility electrolytes

The chemical composition of particulate matter in the atmosphere is complex and not fully known. For many purposes, therefore, it is useful to distinguish three broad categories (1) water-soluble inorganic salts (electrolytes) (2) water-insoluble minerals of crustal origin and (3) organic... 

Since so many of the applications of monodisperse particles are in biochemical fields, it is a fortunate circumstance that most of the syntheses may be carried out with little or no surfactant or other additives. While the early work was usually carried out with conventional surfactants, today many latices with uniform particle size polymers are simply initiated with an inorganic persulfate. Buffers and some other water-soluble electrolytes may be added mainly to modify the particle size distribution. The few water-soluble components that may be present are subsequently removed by such techniques as ion exchange using a mixed bed of ion-exchange resins, centrifugation, dialysis, or water-replacement using suitable membranes or hollow fiber equipment. 

Suspension polymerization occurs in water with the liquid monomer dispersed by agitaliorL The polymer is produced as a dispersed solid phase fiom polymerization of initiator-containing, 10 to 500 pm droplets under kinetics that match those of the bulk reaction of the monomer (7). The suspension is stabilized by insoluble organic or inorganic solids, electrolytes to increase monomer-water interfacial tension, and water soluble polymers that increase aqueous viscosity. Suspension polymerization is commonly used to synthesize two polymers covered in this book, polystyrene and polyvinyl chloride. 

Because a great variety of sources contribute materials to the tropospheric aerosol, it represents a complex mixture of marry substances that additionally depends on the size of the particles. Source characteristics are preserved only in the vicinity of somces. The mixtirre may be divided into three fractiorts water-solirble inorganic salts (electrolytes), water-irrsoluble minerals, and organic compoimds, both soluble in water and insoluble. Table II shows the chemical composition of two boimdary layer aerosols that are typical of marine and of rural continental air. 

Electrolytes are used to promote the exhaustion of direct or reactive dyes on cellulosic fibres they may also be similarly used with vat or sulphur dyes in their leuco forms. In the case of anionic dyes on wool or nylon, however, their role is different as they are used to facilitate levelling rather than exhaustion. In these cases, addition of electrolyte decreases dye uptake due to the competitive absorption of inorganic anions by the fibre and a decrease in ionic attraction between dye and fibre. In most discussions of the effect of electrolyte on dye sorption, attention is given only to the ionic aspects of interaction. In most cases, this does not create a problem and so most adsorption isotherms of water-soluble dyes are interpreted on the basis of Langmuir or Donnan ionic interactions only. There are, however, some observed cases of apparently anomalous behaviour of dyes with respect to electrolytes that cannot be explained by ionic interactions alone. 

The solubility of an ionic dye in water normally increases with temperature, since the enhanced mobility favours electrostatic repulsion between ions rather than closer approach to form aggregates by means of the short-range attractive forces. Addition of a simple inorganic electrolyte, on the other hand, normally lowers the solubility limit at a given temperature. Such additions enhance the ionic character of the aqueous phase and help to stabilise the structure of dye aggregates by forming an electrical double layer within the sheath of clustered water molecules around them. 

Effects of electrolytes on the solubility of organic compounds in aqueous solutions were established empirically more than 100 years ago by Setschenow (1889). He found that the presence of dissolved inorganic salts in an aqueous solution decreases the aqueous solubility of nonpolar and weak polar organic compounds. This effect, known as the salting-out effect, is expressed by the empirical Setschenow formula... 

Curve 1 in Figure 7.14 is the type of behavior characteristic of most un-ionized organic compounds. Curve 2 is typical of inorganic electrolytes and highly hydrated organic compounds. The type of behavior indicated by curve 3 is shown by soluble amphipathic species, especially ionic ones. The break in curve 3 is typical of these compounds however, this degree of sharpness is observed only for highly purified compounds. If impurities are present, the... 

Agglomeration may be accomplished in several ways, such as by controlled adjustment of solids, by extensive shear of the emulsion, or by carefully controlled addition of electrolytes, such as water-soluble salts of inorganic acids, e.g., sodium chloride, potassium hypo-phosphite, potassium chloride, or sodium phosphate. Improved processes rely on the method of addition of the monomers in the distinct stages of polymerization (9). 

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