Systems with significant mutual solubility

When the solubility of B in the solid A is negligible, this equation reduces to  

Equations (5.6) and (5.13) clarify the relation between solubility and wetting. For a given solid metal A, at fixed temperature, a comparatively high value of results from a low value of X, which in turn leads to a low value of tSl (equation (5.13)). This relation between wettability and solubility in metallic systems, through their dependence upon the same energy parameter (i.e., X), was identified long ago by Wassink (1967). 

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At the same time, significant changes in the state of a system can result from fairly moderate deviations in T, for example, the changes in the mutual solubility of both the disperse phase and the dispersion medium components, leading to a radical decrease in a. Typical examples include studies on systems approaching the critical point, (and yet still below the TJ, such as those carried out with binary mixtures of paraffins with moderately polar organic substances, such as oxyquinoline [26,67,68], In these works, the formation of direct, inverse, and bicontinuous microemulsions had been described and analyzed in comparison with the independently determined values of a down to 10" -10" mN/m,... 

As stated previously, the nature of the oil phase and its specific interactions with the surfactant can significantly affect the emulsion characteristics of the system. The polarity of the oil phase (e.g., fatty esters vs. hydrocarbon oils) will determine the proper surfactant solubility requirements and HLB for the primary emulsion, the mutual solubility of the various components, and the transport of materials from the internal to the external phases. The choice of the optimum HLB for the secondary emulsifier can be strongly affected by the concentration of the primary emulsifier employed. For a single-component secondary emulsifier in a Wj/OAVa multiple emulsion, the HLB required to provide maximum multiple emulsion stability is found to increase as the concentration of primary emulsifier in the system... 

The relatively large monomer droplets (generally 2-5ym in diameter) have too small a surface area to capture radicals from the aqueous phase and therefore serve as reservoirs for the diffusion of monomer through the aqueous phase to the pol3onerizing oligomeric radicals, micelles, or polymer particles. Despite the unfavorable statistical probabilities, however, some monomer droplets capture radicals and polymerize to form microscopic or near-microscopic particles (14), and some of these particles which are entirely separate from the main particle size distribution are formed in most batch polymerizations. Polymerization in monomer droplets becomes much more significant when the size of the emulsion droplets is decreased. The use of ionic emulsifier-fatty alcohol mixtures (13) and, later, ionic emulsifier-alkane mixtures (15), allows the preparation of 0.1-0.2ym size styrene monomer droplets, which compete favorably with initiation in micelles and in the aqueous phase as the mechanism of particle nucleation. The mechanism of formation of these "mini-emulsions" has been attributed to the very low solubility of the fatty alcohols and alkanes in water (16) or to the formation of crystalline complexes between the ionic emulsifiers and fatty alcohols (17) the two mechanisms are not mutually exclusive. Thus this mechanism pertains only to special systems. 

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