The conductivity (κ) and Kraft temperature (K T ) measurements were carried out for the binary combinations of dimeric cationic gemini, di(dodecyldimethylammonium bromide) (12-2-12), with alkyl phosphonium and ammonium bromide surfactants to evaluate the mixed micelle formation influenced by head group (i.e. dimeric and monomeric) and hydrophobic tail modifications (i.e. C 1 2 -C 1 6 ). Both studies demonstrated that the dimeric bulky head group of 12-2-12 induced significant steric hindrances in the mixed micelle combinations with phosphonium surfactants as the length of latter's hydrophobic tail exceeds that of 12-2-12. This effect was relatively less prominent with ammonium head group surfactants and almost vanished when instead of 12-2-12, DTAB was taken in combination with phosphonium surfactants.