Surface activity and premicellar aggregation of some novel diquaternary gemini surfactants

A series of novel cationic gemini surfactants, C n H 2n+1 N + (CH 3 ) 2 CH 2 CHOHCHOHCH 2 N + (CH 3 ) 2 C n H 2n+1 ·2Br − , have been synthesized, and their surface properties were investigated in water, 0.1 N NaCl, and 0.1 N NaBr at 25°C. From surface tension‐log molar concentration plots, the pC 20 , critical micelle concentration (CMC), and γ CMC values have been determined, and the area/molecule at the aqueous solution/air interface was calculated. When the number of carbon atoms in the alkyl (hydrophobic) chains is above a certain number, which depends upon the molecular environment, the surface activity of the compounds is less than expected. This appears to be due to formation of small, soluble aggregates below the CMC. Equilibrium constants calculated for this aggregation indicate that a series of oligomers are formed.