Effects of pH and Salt Concentration on Assembly and Disassembly of the PEOX-EI-50/PAA Complex Containing Hydrogen Bonding and Electrostatic Force Dual Interaction

Polymer complexes containing multiple interactions have attracted considerable interest in the development of advanced and multifunctional materials. The fundamental study on multi-interacted polymer complexes helps understand their properties and facilitates rational material design; however, it has been less systematically explored. In this work, a PEOX-EI-50/PAA complex with a dual interaction of hydrogen bonding and electrostatic force is prepared via stepwise interfacial complexation. Quartz crystal microbalance with dissipation (QCM-D) measurements indicate pH-dependent PEOX-EI-50/PAA complexation with the optimal assembly pH at 4. Isothermal titration calorimetry (ITC) results prove the coexistence of the hydrogen bond and electrostatic interaction in the PEOX-EI-50/PAA assembly at specific pH levels and reveal that the high-affinity binding site transits from hydrogen bonding to electrostatic bonding as the pH increases from 3 to 4. In addition, hydrogen bonding could alleviate the inhibition of the electrostatic interaction between complementary polymers by salt, leading to the successful assembly of PEOX-EI-50/PAA in the presence of 1 M NaCl. A pseudo-mass-loss phenomenon is observed during PEOX-EI-50/PAA complexation, which can be further amended by eliminating charge density mismatch through pH/salt concentration adjustment. PEOX-EI-50/PAA exhibits improved pH stability compared with the PEOX/PAA hydrogen-bonding system and exceptional salt stability compared with the PEI/PAA polyelectrolyte pairs, indicating the advantage of the polymer complex with dual interaction.