The binding characteristics of conventional and α,ω-type ionic surfactant mixtures to polyion

The binding isotherms of decyltrimethylammonium bromide (DeTAB) to poly(potassium vinyl sulfate) were determined potentiometrically in mixed solutions with N,N,N,N',N',N'-hexamethyl-1,20-icosanediammonium dibromide (ETMAB) and 1,1'-1,20-icosanediylbispyridinium dibromide (EPB). In both systems, an addition of the alpha,omega-type surfactant causes a remarkable decrease in the slope of the binding isotherm of DeTA(+). In addition, the binding isotherm tended to shift regularly to a low concentration range with increasing concentration of the alpha,omega-type surfactant. A regular solution treatment of the mixed clusters on the polyion chain suggests that substantially all of the added alpha,omega-type ions bind to the polyion under our experimental conditions. The observed binding isotherms can well be reproduced with interchange energies of -0.6 kT for DeTA(+)-ETMA(2+) and -1.6 kT for DeTA(+)-EP2+ pairs in the mixed clusters, respectively.