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F Puisieux

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Dielectric constants of solid-liquid and liquid-liquid systems as a function of composition.

The dielectric constant of a solid substance in the dissolved state may be found by using a solvent with a dielectric constant that remains invariable when the solid substance is dissolved. The slope values obtained from dielectric constant versus concentration plots of the solid substance in two solvents with different dielectric constants are extrapolated or interpolated. The dielectric constant of a solid substance in the dissolved state also can be found directly from the dielectric constants of solutions of the solid in one solvent at two concentrations. The dielectric constants are converted to polarizations, and the two values allow calculations of the polarizations of the solvent and solute separately. From the polarization of the solute, one can calculate its dielectric constant (in dissolved state). Such a procedure is correct only if the dielectric constant is concentration independent.

Chemistry, Pharmaceutical

Emulsion stabilization by non-ionic surfactants: the relevance of surfactant cloud point.

The effect of various additives, electrolytes and non-electrolytes, on the cloud point of non-ionic surfactants has been studied. Additives which salt-out the polyoxyethylene chains of the surfactants cause decreased stability of oil-in-water emulsions by decreasing the true hydrophile-lipophile balance (HLB) of the surfactant; additives such as sodium iodide and propanol salt-in the non-ionic surfactants and result in an increase in the effective or true HLB of the system. The latter additives do not increase the hydration of the polyoxyethylene chains but their effect must be on the structure of water so that the heat of hydration of the chains is altered. Experiments with free films of the aqueous surfactant (Brij 96) show that thinning rates are markedly affected by the additives, but there is little effect on the equilibrium thickness of the films (ca 11 nm). Nonetheless the thickness at the transition from thick film to equilibrium black film decreases with increasing cloud point of the solution indicating increased stability. The importance of structure formation in the liquid film separating the emulsion globules was demonstrated.

Chemical Phenomena

[Tablets. XII].

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Pressure