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Inverse gas chromatography (IGC) has been used for studying the miscibility of anhydrous cationic surfactant mixtures. Dodecyltrimethylammonium bromide (C12TAB), octadecyltrimethylammonium bromide (C18TAB) and their mixtures have been used as stationary phases. In these types of stationary phases, the working temperature was determined by Differential Scanning Calorimetric (DSC) and Inverse Gas Chromatography (IGC) techniques. Values of the interaction parameters between the cationic surfactants obtained at four different compositions of their mixtures and at five temperatures showed that the miscibility depended on the composition and suggested that the interactions became more unfavorable with the increment of C18TAB concentration in the mixtures. The results have been interpreted by comparing the structure of the anhydrous lamellar liquid crystals with that of the lamellar mesophases formed in aqueous solutions. Deviations of the systems from the parameter solubility model have been discussed in terms of the entropy contribution to the Flory-Huggins interaction parameter.12TAB), octadecyltrimethylammonium bromide (C18TAB) and their mixtures have been used as stationary phases. In these types of stationary phases, the working temperature was determined by Differential Scanning Calorimetric (DSC) and Inverse Gas Chromatography (IGC) techniques. Values of the interaction parameters between the cationic surfactants obtained at four different compositions of their mixtures and at five temperatures showed that the miscibility depended on the composition and suggested that the interactions became more unfavorable with the increment of C18TAB concentration in the mixtures. The results have been interpreted by comparing the structure of the anhydrous lamellar liquid crystals with that of the lamellar mesophases formed in aqueous solutions. Deviations of the systems from the parameter solubility model have been discussed in terms of the entropy contribution to the Flory-Huggins interaction parameter.18TAB) and their mixtures have been used as stationary phases. In these types of stationary phases, the working temperature was determined by Differential Scanning Calorimetric (DSC) and Inverse Gas Chromatography (IGC) techniques. Values of the interaction parameters between the cationic surfactants obtained at four different compositions of their mixtures and at five temperatures showed that the miscibility depended on the composition and suggested that the interactions became more unfavorable with the increment of C18TAB concentration in the mixtures. The results have been interpreted by comparing the structure of the anhydrous lamellar liquid crystals with that of the lamellar mesophases formed in aqueous solutions. Deviations of the systems from the parameter solubility model have been discussed in terms of the entropy contribution to the Flory-Huggins interaction parameter.five temperatures showed that the miscibility depended on the composition and suggested that the interactions became more unfavorable with the increment of C18TAB concentration in the mixtures. The results have been interpreted by comparing the structure of the anhydrous lamellar liquid crystals with that of the lamellar mesophases formed in aqueous solutions. Deviations of the systems from the parameter solubility model have been discussed in terms of the entropy contribution to the Flory-Huggins interaction parameter.18TAB concentration in the mixtures. The results have been interpreted by comparing the structure of the anhydrous lamellar liquid crystals with that of the lamellar mesophases formed in aqueous solutions. Deviations of the systems from the parameter solubility model have been discussed in terms of the entropy contribution to the Flory-Huggins interaction parameter.