The Study On Interactions And The Second Virial Coefficients Of Microemulsions

The molar dilution enthalpies of the droplets in the microemulsions consisting of AOT, water and various oils are measured by the Isothermal Titration Microcalorimetry (ITC). According to the molar dilution enthalpies, the second Virial coefficients are determined and the interactions between the droplets are discussed. This thesis consists of two sections:(1) The titration heats from changing concentrations of water/AOT/toluene and water/AOT/cyclohexane microemulsions are determined and it is found that the dilution processes are both endothermal, which indicates that the aggregation of the droplets is driven by the enthalpy and the interaction energy between the droplets is negative (attractive energy). The square-well potential between particles is used to calculate the enthalpy contributions to the second virial coefficients. The entropy contributions to the second Virial coefficients then are obtained by using the total second virial coefficients determined by the light scattering. The corresponding enthalpy and entropy for the droplets aggregation are also obtained.(2) The titration heats for water/AOT/n-decane and water/AOT/isooctane microemulsions are determined by ITC for various molar ratios of water to AOT. It is found that the dilution enthalpies of water/AOT/n-decane change from positive to negative as the ratio increasing, which indicates that the driven force of the aggregation of the droplets changes from the enthalpy to the entropy and the interactions between droplets change form the attraction to the repulsion. We calculate the second Virial coefficients and the interaction energies through the square-well potential for the water/AOT/n-decane microemulsions with small molar ratios of water to AOT. The dilution enthalpies of water/AOT/isooctane are found to be all negative. This implies that the aggregation of the droplets is driven by the entropy, which is in agreement with the result of light scattering.