Mixtures of Anionic and Cationic Surfactants at Critical Micelle Concentration

Hamdan S, Ku Bulat, K. H., Laili C.R., Faujan F.  B. H.1 and Zaizi M. D1

¹Chemical Sciences Unit, Faculty of Sciences and Professional Arts, Universiti Putra Malaysia Terengganu, UPMT 21030, Mengabang Telipot, K. Terengganu, Terengganu, (Malaysia) ²Chemistry Department, Faculty of Science and Environmental Studies, Universiti Putra Malaysia, UPM 43400 Serdang, Selangor, (Malaysia)

Two oppositely charged surfactants namely cetyltrimethylammonium bromide (CTAB) and sodium octanoate was investigated as mixtures at their critical micelle concentration, cmc. Surface tension analysis was used to determine the miscibility of the aqueous mixtures at variable mole fraction of CTAB. A decrease in the cmc value of the mixtures was observed with increasing mole fraction of CTAB. The mixed surfactants were slightly nonideal with the deviation parameter of –0.94. The mole fraction of CTAB in the aqueous mixed solution was less than the mole fraction CTAB in the mixed micelle at the cmc. This suggested that CTAB is geometrically favourable for the formation of the mixed micelle.

Mixed surfactant; critical micelle concentration; surface tension