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

Area of Science:

• Materials Science
• Polymer Chemistry
• Supramolecular Chemistry

Background:

• Molecular granular materials (MGMs) offer unique viscoelastic properties but are challenging to synthesize covalently.
• Polyhedral oligomeric silsesquioxanes (POSS) are versatile building blocks for advanced materials.

Purpose of the Study:

• To develop a supramolecular strategy for constructing MGMs using ionic functionalization of POSS derivatives.
• To investigate the structure-property relationships of ionic MGMs and their mechanical responses.

Main Methods:

• Ionic functionalization of octyl POSS (OPOSS) with ammonium (AOPOSS) or zwitterionic (ZOPOSS) groups.
• Characterization of self-assembly, phase behavior, and viscoelastic properties using techniques like broadband dielectric spectroscopy.

Main Results:

• Amphiphilic POSS derivatives (AOPOSS and ZOPOSS) self-assemble into ordered (A15 phase) or disordered microphase-separated structures.
• Ionic MGMs exhibit significant elastic behavior up to 150 K above their glass transition temperatures.
• Hierarchical relaxation processes are governed by ionic interactions and structural packing, influencing mechanical response.

Conclusions:

• Ionic functionalization provides a facile route to design MGMs with tunable hierarchical structures and enhanced high-temperature elasticity.
• The strength of ionic interactions is a key factor in controlling ordering and dynamics in these materials.
• This approach offers a new paradigm for developing advanced functional materials.