Polyelectrolyte Complexation When Considering the Counterion-Mediated Hydrogen Bonding

In this work, we have investigated a pH-modulated complexation between two oppositely charged strong polyelectrolytes to demonstrate the effect of counterion-mediated hydrogen bonding (CMHB) on polyelectrolyte complexation. We have found that such a pH-modulated complexation cannot be understood without considering the CMHB. Thermodynamically, the effect of CMHB on the polyelectrolyte complexation is manifested by the alteration of both enthalpic and entropic contributions to the free energy change. The pH-dependent intrinsic ion-pairing and complex coacervation processes of the polyelectrolyte complexation can be understood when considering the CMHB. Our study demonstrates that both the extent of polyelectrolyte complex formation in bulk solutions and the formation of polyelectrolyte multilayers on surfaces are controlled by the pH-dependent intrinsic ion-pairing process. Furthermore, on the basis of the pH-dependent intrinsic ion pairing, the properties of the multilayers can be tuned by pH. This work provides a new strategy to control the polyelectrolyte complexation with counterions and will inspire new ideas for building advanced polyelectrolyte materials.