Kinetics of polyelectrolyte complexation studied by the conductance stopped-flow technique. The systems polyacrylate–polybrene and poly(ethylene sulphonate)–polyethylenimine

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Abstract
Polyelectrolyte complexation between weakly acidic (or basis) macroions and strongly basic (or acidic) ones, i.e. sodium polyacrylate (NaPAA)+ polybrene(PB) and polyethylenimine (PEI)+ sodium poly(ethylene sulphonate)(NaPES), has been analysed. The equilibrium association constants (K1) of PAA–+ PB+ and PEIH++ PES– and those (K2) of PAA + PB+ and PEI + PES– are estimated from pH measurements. K1(105–107 dm3 mol–1) increases with degree of neutralization (α) of weak macroions and also with decreasing polymer concentration. K2 is insensitive to α and to the concentration. Two relaxation times (τ1 and τ2) are obtained in the traces of the relaxations of the polyelectrolyte complexations from conductance stopped-flow measurements and are assigned to a fast association process in complexation and a slow reorientation of the complex formed, respectively. The association (kf) and dissociation (kb) rates are between 1 × 106 and 1.3 × 107 dm3 mol–1 s–1 and between 0.1 and 10 s–1. kf first increases with α but then decreases at large α, whereas kf is either insensitive or decreases with α. Both the enthalpy and entropy of activation of the complexation increase drastically with increasing α, which suggests significant hydration of the macroions and the importance of the dehydration of water molecules in the course of complexation.