Ionic Assembly of Molecular Clusters toward Hierarchically Ordered Granular Materials with Tunable Viscoelasticity

Molecular granular materials (MGMs) assembled from subnanometer clusters exhibit unique viscoelasticity but are often limited by complex covalent synthesis. Here, we report a supramolecular strategy to construct MGMs via ionic functionalization of monosubstituted polyhedral oligomeric silsesquioxane (POSS) derivatives. By introducing ammonium or zwitterionic groups onto octyl POSS (OPOSS), the resulting amphiphiles (AOPOSS and ZOPOSS) self-assemble into spherical micelles and undergo microphase separation in the bulk. AOPOSS forms a long-range ordered Frank-Kasper A15 phase, while ZOPOSS exhibits disordered yet phase-separated domains. Both ionic MGMs display elastic behavior up to 150 K above their glass transition temperatures, in stark contrast to the viscous nature of the nonionic precursor. Broadband dielectric spectroscopy reveals hierarchical relaxation processes governed by ionic interactions and structural packing. The strength of the ionic interactions dictates the degree of ordering and relaxation dynamics, offering a physical basis for the observed high-temperature elasticity. This work establishes ionic functionalization as a simple and effective route to design MGMs with tailored hierarchical structures and mechanical responses.