Viscosity and the phenomenon of percolation in microemulsions

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Abstract
The viscosity of water/AOT/oil microemulsions (undecane, isooctane, cyclohexane) has been studied as a function of the molar ratio n=[water]/[AOT] and the volume fraction φ (water + AOT) at T=25 °C. [Here AOT is an abbreviation for sodium bis(2-ethylhexyl)sulfosuccinate.] At constant φ and variable n, the presence of a maximum viscosity can be observed. The results are discussed in connection with a percolation model and a very good qualitative agreement is obtained. The results are compatible with those obtained previously on the conductivity and complex permittivity of these microemulsions. The results show the importance of the idea of ‘‘percolation threshold lines.’’ Emphasis is placed on the importance of interactions and on the necessity of following an experimental procedure involving constant interaction (for either ternary or quaternary systems).