Frequency dependence of dielectric loss of w/o microemulsions and low temperature dielectric behavior

Low frequency dielectric measurements (5 Hz–100 MHz) in parallel with Differential Scanning Calorimetry were used to study the behavior of a water-in-dodecane microemulsion as a function of increasing water content, C-mass fraction, in the interval 0.024≤C≤0.4, upon decreasing temperature from 20°C down to −190°C. The presence of “free” and “interfacial” water molecules was evidenced and a differentiation obtained between w/o dispersions, depending on whether they possess a “free” water fraction. Polydispersity was demonstrated by means of dielectric loss analysis. A mechanism based on the hydration of hydrophilic groups of surface active molecules is proposed to account for the disappearance of “free” water upon ageing of samples exhibiting time dependent phenomena. The dielectric properties of the system against both frequency and temperature are discussed in terms of the calorimetric results.