Unveiling the Architectural Impact on the Salt-Tunable Adhesion Performance and Toughness of Polyzwitterions

Developing tough adhesives with superior strength and ductility is challenging yet highly sought-after. In this work, we address a strategic approach to achieving diverse toughness and performance by meticulously harnessing weak electrostatic interactions. Two polyzwitterions (PZIs), derived from sulfobetaine methacrylate (SBMA), of different topologies: bottlebrush (BB-PSBMA) and linear (L-PSBMA), were designed. BB-PSBMA was synthesized using a rational "grafting-from" strategy, while L-PSBMA was prepared via atom transfer radical polymerization. Despite their architectural disparities, both PZIs demonstrated a comparable substantial lap-shear adhesion strength of ∼0.4 MPa. Intriguingly, the introduction of NaCl during adhesive preparation revealed contrasting adhesion behaviors. BB-PSBMA transitioned from a strong-brittle to strong-ductile adhesive upon the addition of 70 mM NaCl, evidenced by a 77.4% increase in the work of debonding, i.e., toughness. Further increases in NaCl concentration continued to impart the ductile properties to BB-PSBMA. Conversely, L-PSBMA adhesive predominantly transformed from strong-brittle to ductile regardless of the salt content. We propose a synergistic mechanism involving viscosity-governed optimal adhesion-cohesion balance and mechanical energy dissipation through sacrificial electrostatic association to elucidate the strong and ductile nature of the BB-PSBMA adhesive at 70 mM NaCl. Our findings emphasize the significance of precise control over architecture and salt concentration is necessary in constructing adhesives with enhanced toughness and performance.