In the master’s thesis, we investigated mixtures of two cationic surfactants from the group of decyl-, dodecyl- or tetradecyltrimethylammonium chloride. We were interested in the influence of the ration between surfactants with different tail lengths on the critical micelle concentration (cmc), the composition of the solution and micelles, and the thermodynamics of mixed micelle formation. The cmc values and degree of micelle ionization were estimated by measuring the electrical conductivity of the solutions. The values were then used to calculate the standard Gibbs free energy (free enthalpy), standard enthalpy and standard entropy of micellization, and to calculate the micelle composition. The calculated enthalpies and cmc estimations of the surfactant TTAC and the mixtures TTAC-DeTAC were then compared with calorimetric measurements. From the measurements we concluded that the cmc of the mixtures strongly depends on the ration between the two surfactants and is determined by the surfactant with the longer tail. The mixtures values of the free enthalpy of micellization are between those of the puresurfactants and increase linearly with the mole fraction of DeTAC. When comparing the calorimetry and conductivity measurements we found that both methods can be used to determine the cmc values of mixtures. The calculated enthalpies of pure surfactants are in most cases in good agreement with the measured ones, with some deviations at low temperatures. The micelle composition was calculated numerically using an equation that connects the cmc of pure surfactants and their mixtures, from the results we concluded that the micelles at cmc contain a relatively large mole fraction of the surfactant with the longer tail.
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