Journal of Surface Science and Technology

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Adsorption of Ionic Surfactants at the Alumina/Water Interface


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1 Department of Food Technology and Biochemical Engineering, Jadavpur University, Calcutta-700 032, India
     

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Adsorption of cationic and anionic surfactants from aqueous solutions on alumina particles has been studied. The alumina used was characterised by measuring isoelectric pH and the specific surface area. Adsorption experiments of cationic surfactants have been done on negatively charged alumina and of anionic surfactant on positively charged alumina. Adsorption is found to depend on the chain length of the surfactants. DTAB was found to be adsorbed perpendicularly while CTAB was almost flat at the interface. MTAB showed intermediate orientation. It was also observed that the saturation adsorption of surfactants occured at concentrations (csc) often not identical with cmc, but in most cases csc was less than cmc. SDS showed interfacial coagulation behaviour both at 30°C and 50°C. Increase of ionic strength decreases the amount of adsorption, Interchain cohesion within adsorbed monolayer was weak for CTAB adsorption, but was rather strong in case of MTAB and DTAB. As a result of this, some of the isotherms of MTAB DTAB showed steps. The results have been analysed according to thermodynamic principles.
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  • Adsorption of Ionic Surfactants at the Alumina/Water Interface

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Authors

L. Ghosh
Department of Food Technology and Biochemical Engineering, Jadavpur University, Calcutta-700 032, India
K. P. Das
Department of Food Technology and Biochemical Engineering, Jadavpur University, Calcutta-700 032, India
D. K. Chattoraj
Department of Food Technology and Biochemical Engineering, Jadavpur University, Calcutta-700 032, India

Abstract


Adsorption of cationic and anionic surfactants from aqueous solutions on alumina particles has been studied. The alumina used was characterised by measuring isoelectric pH and the specific surface area. Adsorption experiments of cationic surfactants have been done on negatively charged alumina and of anionic surfactant on positively charged alumina. Adsorption is found to depend on the chain length of the surfactants. DTAB was found to be adsorbed perpendicularly while CTAB was almost flat at the interface. MTAB showed intermediate orientation. It was also observed that the saturation adsorption of surfactants occured at concentrations (csc) often not identical with cmc, but in most cases csc was less than cmc. SDS showed interfacial coagulation behaviour both at 30°C and 50°C. Increase of ionic strength decreases the amount of adsorption, Interchain cohesion within adsorbed monolayer was weak for CTAB adsorption, but was rather strong in case of MTAB and DTAB. As a result of this, some of the isotherms of MTAB DTAB showed steps. The results have been analysed according to thermodynamic principles.