Mixed micelles in the presence of macrocyclic additives: A host-guest conductometric study

The conductances of sodium dodecylsulphate (SDS) + sodium decylsulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) + tetradecyltrimethylammonium bromide (TTAB) over the entire mole fraction range of SDS (alpha(SDS)) or DeTAB (alpha(DeTAB)) were measured in water, 18-crown-6 ether + water (CR + W) and beta-cyclodextrin + water (CYC + W) mixtures at fixed 4 mM and 8 mM of CR or CYC in their respective binary mixtures at 30 degrees C. The conductivity plots for SDS + SDeS mixtures show a single break whereas two breaks are observed at most of the alpha(DeTAB) for DeTAB + TTAB mixtures. From the break in the conductivity data, the mixed critical micellar concentration (cmc) and degree of counter-ion association (chi) were computed. The first break corresponds to the classical cmc of TTAB is termed as the first cmc (C-1) and the second break which is observed at concentrations about 4 times the first one, corresponding to the classical cmc of DeTAB and is considered to be the second cmc (C-2). The non-ideality in SDS + SDeS mixtures has been evaluated by using the regular solution theory and it has been observed that the mixture is close to ideal in the absence and presence of additives. The variation in C-1, C-2 and chi(1), chi(2) for DeTAB + TTAB has been discussed in terms of the mixed micelle formation which are predominantly rich in the TTAB and DeTAB monomers respectively.