Evidence of a two-step process and pathway dependency in the thermodynamics of poly(diallyldimethylammonium chloride)/poly(sodium acrylate) complexation

摘要

Recent studies have pointed the importance of polyelectrolyte assembly in theelaboration of innovative nanomaterials. Beyond their structures, manyimportant questions on the thermodynamics of association remain to be answered.Here, we investigate the complexation between poly(diallyldimethylammoniumchloride) (PDADMAC) and poly(sodium acrylate) (PANa) chains using a combinationof three techniques: isothermal titration calorimetry (ITC), static and dynamiclight scattering and electrophoresis. Upon addition of PDADMAC to PANa orvice-versa, the results obtained by the different techniques agree well witheach other, and reveal a two-step process. The primary process is the formationof highly charged polyelectrolyte complexes of sizes 100 nm. The secondaryprocess is the transition towards a coacervate phase made of rich and poorpolymer droplets. The binding isotherms measured are accounted for using aphenomenological model that provides the thermodynamic parameters for eachreaction. Small positive enthalpies and large positive entropies consistentwith a counterion release scenario are found throughout this study. Beyond,this work stresses the importance of the underestimated formulation pathway ormixing order in polyelectrolyte complexation.