Polysiloxane Supramolecular Elastomers via Programmable Ionic-Hydrogen-Bonded Aggregates

Abstract

While nanoscale aggregates as dynamic crosslinks enhance supramolecular elastomers, systematically elucidating how aggregate parameters are regulated and dictate mechanical responses remains challenging. Here, we fabricate polysiloxane-based supramolecular elastomers with varied aggregate structural parameters by leveraging the thermodynamic incompatibility between strongly associative ion pairs and the weakly polar siloxane backbone, driving spontaneous microphase separation. Three primary design parameters influence aggregate structure and dictate mechanical behavior and failure mechanisms: interaction strength, spacer length, and preparation methods (direct, stepwise, and simultaneous crosslinking). SAXS, TEM, and AFM reveal clear differences in aggregate structures, a trend consistent with rheological and relaxation behavior. Interaction strength drives phase separation, governing aggregate formation and stability. Spacer length governs interaggregate distance (d) and chain mobility, balancing modulus, energy dissipation, and creep recovery. Preparation methods dictate the spatial distribution of aggregates. Compared with the direct (AU) and simultaneous (AX) crosslinked networks, the stepwise crosslinked network (AUU) promotes a transition from discrete, island-like aggregates to locally interconnected, percolating aggregate networks, which fundamentally alters the stress-transfer mechanism and leads to a distinct trade-off: enhanced static load-bearing capacity and dynamic adaptability at the cost of increased notch sensitivity. This work establishes systematic correlations between tunable aggregate parameters (d, size, and connectivity) and the dynamic/static properties, providing guidelines for the design of supramolecular elastomers.