Nanoscale Hierarchical Structures Formed by Sequence-Defined Polycations and Homopolyanions for High Salt-Tolerance Adhesives

The bridges formed by polycationic chains in the nanoslits can induce attraction interactions, but this bridge adhesion is markedly weak and quickly diminishing when exposed to high salinity conditions. In this work, we propose an ingenious method to enhance the adhesive strength in systems with high salt concentrations by introducing short homopolyanion (HPA) chains into the sequence-defined polycation (SDPC) solutions. The effects of SDPC/HPA chain lengths, monomer sequence distributions, monomer concentrations, and surface charge density were systematically investigated by using polymer density functional theory and molecular dynamics simulation. The results show that the origin of the strong adhesion is the spontaneous formation of polyelectrolyte multilayers (PEMs) induced by HPAs. It is fascinating to observe that these strong adhesive interactions induced by PEMs exhibit high salt tolerance; i.e., the peel force (which can be used to denote the adhesion performance) does not decline even at high salt concentrations. In addition, the increase in the chain length of SDPC is beneficial to the formation of PEMs, resulting in a stronger peel force. Moreover, among the alternating [A], tapered [T], and reversely tapered [R] SDPCs, the systems with [T]-sequence PC/HPA exhibit optimal adhesive performance due to their favorable conditions for the formation of PEMs, characterized by the weakest decentralization effect of electrostatic attraction.