Effect of salts on the conductance of polylectrolyte solutions

Abstract

Electrical conductance of aliphatic x , y -ionenes as well as some acidic polyelectrolytes such as poly(styrene sulfonic acid) (PSS) and poly(acrylic acid) (PAA) in solution was measured with special attention to the effect of salt added. The conductance measurements exhibited a marked departure from the additivity in the presence of salt, contrary to the case of counterion activity. Namely, the conductance of the ionene solution was always lower than the sum of those of salt-free ionene solution and corresponding salt solution. The relative departure was almost unchanged when the polyion concentration was lowered to 5×10 −5 N l −1 , suggesting that this phenomenon is interpreted as an intramolecular process. The deviation was less pronounced in case of ionene-fluoride, a hydrophilic counterion, as well as other polyelectrolytes tested such as potassium salts of PSS and PAA. The deviation reduced by changing degree of neutralization by addition of OH − , which is understood as partial replacement of the counterion by OH − . These results are discussed in terms of chain flexibility as well as counterion specificity.