Dependency of the mobility of carboxymethylated cellulosic polyions on the nature of their counterions

Abstract

In this paper, we propose a new approach in order to interpret the dependency of the conductibility of carboxymethylated cellulosic polyelectrolytes XCMC1, XCMC2, XCMC3 in water at 25 °C, with their alkali counterions (X ≡ Li+, Na+ and K+) or ammonium counterions (X ≡ Et4N+ and Bu4N+).The 750 ring-blocks of each CMCi chain are randomly substituted by CH2COO groups, of electric charge (eαX), where αX is the degree of dissociation of the counterions X. It is found that for a given CX ≤ 7 10−3 mol·l−1, the experimental equivalent conductivity λP,X of the polyion CMCi decreases as follows: λP, K+ > λP, Na+ ≥ λP,Li+ > λP,Et4N+ > λP,Bu4N+. This behavior cannot be explained either by a specific ionic condensation, or in terms of hydrodynamic friction or ionic friction undergone by the polyion, or in terms of change of configuration of the polyions (ellipsoidal configuration). However, calculations taking into account the dielectric friction effect according to our new general formula, recently published, giving the dielectric friction coefficient, βPdf, for pearl-necklace-like polyelectrolyte chains, allowed to obtain good convergence between experimental and theoretical results. This new approach improves the interpretations given by Manning and Vink in terms of electrophoretic effect only.