Novel ionic liquid-type Gemini surfactants: Synthesis, surface property and antimicrobial activity

Novel quaternary ammonium Gemini surfactants, which turned out to be ionic liquids due to the intermolecular hydrogen bonding formed from hydroxyl groups in the spacers, were synthesized and characterized by IR, 1H NMR, 13C NMR and mass spectra. The surface properties of the Gemini surfactants were investigated by means of surface tension measurements. Surface tension parameters including surface excess concentration, Гcmc, surface area demand per molecule, Acmc, efficiency in surface tension reduction, pC20, the effectiveness of surface tension reduction, γcmc, critical micelle concentration, CMC, and standard free energy of micellization, Δ G a d s 0 and Δ G m i c 0 were obtained. The results indicated that compared with those of their corresponding conventional single-chain surfactant counterparts, these novel Gemini surfactants exhibited lower CMC values and greater efficiency in lowering the surface tension of water. The foamability and foam stability of these Gemini surfactants decreased with the increase in the length of the spacer chain. Gemini surfactants with alkyl chains of moderate length (C12 or C14) showed the best foamability and the highest foam stability. Some of the Gemini surfactants exhibited antimicrobial activity against Gram-negative bacteria Escherichia coli.