Micellar and antimicrobial activities of ionic surfactants in aqueous solutions of synthesized tetraalkylammonium based ionic liquids

A series of quaternary ammonium based ionic liquids (ILs) containing tetraalkylammonium cation has been synthesized and characterised by NMR as well as FT-IR analysis. Then their effect on aggregation behaviour of an anionic surfactant, Sodium dodecylsulphate (SDS) and a cationic surfactant, Dodecyltrimethylammonium bromide (DTAB) has been investigated using conductometric, fluorescence (emission spectra) and UV-vis (absorption spectra) techniques. To gain better insight into colloidal behaviour of surfactant in ILs, the critical micelle concentration (CMC) of surfactant has been calculated in the absence and presence of IL. The addition of IL has a depressing effect on CMC values of studied surfactants in aqueous medium. Also the observed variation in CMC values has been discussed in terms of structural modulation in surfactant-water complex caused by these additives. Furthermore, the thermodynamic parameters of micelle formation viz. change in standard free energy (Delta G(m)(0)), change in standard enthalpy (Delta H-m(0)) and change in standard entropy have been investigated from the dependence of CMC on temperature using charged pseudo-phase model of micellization. All the calculated parameters have been used to elucidate the electrostatic and hydrophobic contributions of IL for the building up of the micellar aggregates of the surfactant. The effect of these ILs on the antibacterial activity of surfactants has also been tested by measuring zone of inhibition and minimum inhibitory concentration (MIC) for DTAB and SDS in the presence of ILs against gram positive and gram negative bacterial species.