Functional Molecular Granular Materials: Advances and Perspectives

Abstract

Molecular granular materials (MGMs) are constructed with sub-nanoscale molecular clusters (MCs) as the building units and they have recently been observed to possess enriched functionalities distinct from granular materials of colloid nanoparticles. Herein, the birth and recent research advances in MGMs are summarized with the topics covering the precise synthesis of MC assemblies with target topologies, the hierarchical relaxation dynamics and tuneable viscoelasticity, impact-resistant capacity, and proton conduc-[a

Photoresponsive Viscoelasticity of the Granular Materials of Azobenzene-Bearing Molecular Nanoparticles

“…The sizes of the building unit can be decreased further to even sub-nm scale and the emergent material systems demonstrate hierarchical relaxation dynamics and broadly tunable viscoelasticity that is used to be the unique properties of polymers. , The so-called molecular granular materials (MGMs) possess robust elasticity even 100 K above their apparent glass transition temperatures ( T g ) from thermal analysis, which is distinct from polymers . The engineering of topologies and/or deformability of MGM units can be used to regulate the viscoelasticity of MGMs. ,, Nevertheless, the manipulation of MGM’s viscoelasticity via external stimulus is still in blank, limiting their applications in smart materials.…”

Unique Viscoelasticity and Hierarchical Relaxation Dynamics of Molecular Granular Materials

“…Molecular clusters (MCs) are ensembles of bound atoms or molecules with sizes ranging from the subnanometer range to 10 nm. − Remarkably different from colloidal NPs, they possess atomically precise molecular structures and well-characterized surface sites. , Their surfaces can be precisely tailored with versatile functional groups to tune the interactions among MCs. Using MCs as building blocks, MC-based MGMs with enriched topologies and adjustable sizes can be feasibly synthesized. ,− The MGMs prepared thusly share the characteristics of well-defined structures and hierarchical relaxation dynamics behaviors . To date, MGMs have demonstrated broad applications for the resistance of high-speed impact, , ion conduction, − and gas separation, − which, we believe, are strongly related to their hierarchical relaxation dynamics.…”

“…16,21−23 The MGMs prepared thusly share the characteristics of well-defined structures and hierarchical relaxation dynamics behaviors. 24 To date, MGMs have demonstrated broad applications for the resistance of high-speed impact, 13,25 ion conduction, 26−29 and gas separation, 30−32 dynamics studies, broadband dielectric spectroscopy (BDS) probes the fluctuations of electronic dipoles (e.g., dipolar molecules) under an applied electric field. 33 Typical relaxation dynamics processes, including ion diffusion, polymer chain relaxation, and particle collective motion, can be precisely located over extremely broad temporal ranges (10 −6 −10 12 Hz).…”

Exploration of Molecular Nanoparticles as Soft Structural Materials and Their Structure–Property Relationship

“…30 The MNPs assembled from MC units, though possessing small sizes, demonstrate anomalous hierarchical dynamics arising from MC surface groups, MC (sub)diffusive motions, and cooperative dynamics among MC assemblies. 31,32 Nonetheless, a clear understanding of MNPs' structure−property relationships is still missing. Specifically, quantitative correlations between hierarchical dynamics and mechanical properties are urgently demanded to differentiate them from polymers and, more importantly, help to guide the material by design of MNPs for soft structure materials.…”

“…Nanoscale molecular clusters (MCs) equipped with atomically accurate architectures and quantitative surface-active sites have been well-established, and they can be further engineered into molecular nanoparticles (MNPs) with enriched topologies. − Interestingly, the star-shaped MNPs demonstrate the properties of viscoelasticity although entanglements and strong supramolecular interactions can be excluded. , Generally, viscoelasticity is expected to be the unique properties of polymeric materials because it requires hierarchical structural relaxation dynamics . The MNPs assembled from MC units, though possessing small sizes, demonstrate anomalous hierarchical dynamics arising from MC surface groups, MC (sub)­diffusive motions, and cooperative dynamics among MC assemblies. , Nonetheless, a clear understanding of MNPs’ structure–property relationships is still missing. Specifically, quantitative correlations between hierarchical dynamics and mechanical properties are urgently demanded to differentiate them from polymers and, more importantly, help to guide the material by design of MNPs for soft structure materials.…”