Ion exchange equilibrium in polyelectrolyte solutions through the CHCl3/water interface

A model to determine ion exchange constants, K,,, in polyelectrolytes throu gh interfaces is proposed. The model is tested through the chloroform/water interface using the bromide salts of n-alkylpyridinium polyelectrolytes (n =6, 8, 10) in the organic phase and the sodium salts of benzene sulfonate, 4-methylbenzene sulfonate and 4-ethylbenzene sulfonate in the aqueous phase . The results show good agreement with the initial linearity predicted by t he model, but a limit of saturation is reached as the bromide anions are ex changed by the amphipathic counterions of increasing size. The ion exchange constants increase with the size of the sulfonate counterions and with the length of the polyelectrolyte side chain. Benzene sulfonate and bromide io ns show similar affinity for the polyelectrolyte, as inferred from the valu es of K-ex exchange constants. The results are in good agreement with the r eported K-ex values in a micellar system with a trimethyl ammonium polar he ad when compared with extrapolated K-ex for the same type of ion exchange. (C) 2001 Academic Press.