Multicomponent Diffusion of Distearyldimethylammonium Polyelectrolyte Solutions in the Presence of Salt: Coupled Transport of Sodium Chloride

Abstract

A sensitive conductance method has been used to determine binary and ternary diffusion coefficients of distearyldimethylammonium chloride, bromide, and hydroxide (DSDMACl, DSDMABr, and DSDMAOH) in aqueous solutions in the absence and presence of salt. Experiments were conducted above and below the critical micelle concentration (CMC) at 25 °C, and the concentration of salt, when present, was 0.015 M NaX (X = Cl, OH, Br). The experiments reveal that diffusion of DSDMA chloride, bromide, and especially hydroxide induces concurrent flow of NaCl, NaBr, and NaOH, respectively. Also, diffusion of DSDMAX in the presence of NaCl drives countertransport of DSDMACl or DSDMAOH. At pH 7.5 and an ionic strength of 0.015 M, each mole of diffusing DSDMACl (Nagg = 72, α = 0.15) cotransports 9.0 mol of NaCl. However, coupled flow of NaCl decreases as the solution pH approaches 5.2 and is almost zero at pH 4.5. The corresponding value for diffusing DSDMAOH at pH 7.5 is about 120 mol of NaCl. At pH 6.5 only 10 mol of NaCl a...