Effect of Long‐Chain Length on the Surface Activities of Zwitterionic Imidazolium‐Based Surfactants: 1‐Carboxymethyl‐3‐alkylimidazolium Inner Salts

Zwitterionic imidazolium‐based surfactants, namely 1‐carboxymethyl‐3‐alkyl imidazolium inner salts (C n imCM, n = 10, 12, and 14), were synthesized. Their molecule structures were characterized by means of electrospray ionization mass spectrometry (ESI–MS), 1 H nuclear magnetic resonance ( 1 H NMR) and elemental analysis. Compared to the structurally related N ‐alkylbetaines (C n H 2 n +1 N + (CH 3 ) 2 CH 2 COO − ), the CMCs of C n imCM are smaller than those of N ‐alkylbetaines. The effect of the long‐chain length on the typical physicochemical properties of C n imCM was studied. It is found that the lengthening of the long‐chain enhances the surface activity of C n imCM. The tendency for C n imCM surfactants is similar to the case of the structurally related traditional zwitterionic N ‐alkylbetaines.