The Effect of a Background Electrolyte on the Viscosity of Aqueous Dodecyltrimethylammonium Bromide Solutions

摘要

Conductometry and viscometry have been employed to study the effect of a background electrolyte (KBr) taken in concentrations of 0.03 and 0.1 M on the critical micelle concentration of dodecyltrimethylammonium bromide (D cent DB) and the dependence of relative viscosity eta/eta(0) of D12D cent DB micellar solutions on the overall surfactant concentration. It has been found that, as a first approximation, each of these dependences may be represented as the sum of two linear portions. Concentrations c* of D12D cent DB micellar solutions, which correspond to the inflections between the two linear portions in the concentration curves of relative viscosity, have been determined. The Einstein equation eta/eta(0) = 1 + 2.5p (p is the volume fraction of the dispersed phase and 2.5 is a theoretical parameter that takes into account the spherical shape of the particles) has been transformed into a form corresponding to the concentration dependence of the relative viscosity on the overall surfactant concentration to make it applicable to the consideration of low-concentration systems, which are uncomplicated by intermicellar interaction. In particular, the applicability of the above equation for estimating micelle radii has been studied. It has been shown that the (eta/eta(0)-1) = f(c/N (01)-1) concentration dependences represented in bilogarithmic coordinates (c is the overall D12D cent DB concentration and c (01) is the critical micelle concentration) are linear in the absence of a significant intermicellar interaction and have slopes equal to unity. This fact may be considered as a criterion for the applicability of the Einstein equation to micellar solutions.