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.