PHYSICO-CHEMICAL AND TRANSPORT PROPERTIES OF DODECANE-IN-WATER EMULSIONS STABILIZED WITH IONIC AND NONIONIC SURFACTANTS

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Abstract
Physico-chemical and transport properties of dodecane-in-water emulsions have been studied with respect to the type and the concentration of the emulsifier. Emulsions properties are related to the particle size which depends greatly on the technique of emulsification and the surfactant concentration. As surfactant concentration increases and particle size decreases, viscosity of the emulsions increases, more rapidly with the nonionic surfactant than with the ionic ones. In the ionic emulsions, the dependence of the conductivity upon the volume fraction ϕ of the disperse phase follows the equations of Maxwell or Bruggeman in which is included a term Kd representing the conductivity of the disperse phase. On the contrary, in the nonionic ones, the conductivity is lowered to a larger extent than predictable from the same equations with Kd = 0. Relative viscosities and conductivities both follow an equation of the form Ke = ( 1 - ϕ)m and nr = ( 1 - ϕ) Polarographic diffusion coefficients of T+ ions in nonionic emulsions fit to the relation D = DO ( 1 - ϕ )n where the exponent n has the same value as that derived for viscosity except in the most viscous emulsion where n lies between viscosity and conductivity exponents. When an hydrophobic solute (ferrocene) is contained in the disperse phase, the oxidation current at a rotating disk electrode depends on the surfactant, the surfactant concentration and the particle size owing to the technique used to prepare the emulsion.

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