Physical networks from entropy-driven non-covalent interactions

Abstract

Physical networks typically employ enthalpy-dominated crosslinking interactions that become more dynamic at elevated temperatures, leading to network softening. Moreover, standard mathematical frameworks such as time-temperature superposition assume network softening and faster dynamics at elevated temperatures. Yet, deriving a mathematical framework connecting the crosslinking thermodynamics to the temperature-dependent viscoelasticity of physical networks suggests the possibility for entropy-driven crosslinking interactions to provide alternative temperature dependencies. This framework illustrates that temperature negligibly affects crosslink density in reported systems, but drastically influences crosslink dynamics. While the dissociation rate of enthalpy-driven crosslinks is accelerated at elevated temperatures, the dissociation rate of entropy-driven crosslinks is negligibly affected or even slowed under these conditions. Here we report an entropy-driven physical network based on polymer-nanoparticle interactions that exhibits mechanical properties that are invariant with temperature. These studies provide a foundation for designing and characterizing entropy-driven physical crosslinking motifs and demonstrate how these physical networks access thermal properties that are not observed in current physical networks.

Skin-like mechanoresponsive self-healing ionic elastomer from supramolecular zwitterionic network

“…Conclusively, the increasing temperature would lead to the enhancement of ionic complexation and weakening of H-bonding, resulting in the more pronounced deprotonation degree of PAA and thus improved proton conductivity. From the energetical view, the PAA dimeric H-bonding could be enthalpy-driven with temperature-induced weakening effect, while the enhanced betaine ionic complexation at elevated temperatures implies an uncommon entropy-driven physical crosslinking interaction, which may be caused by the desolvation events that give rise to large increases in translational entropy of solvent molecules 43 .…”

Complementary Dynamic Chemistries for Multifunctional Polymeric Materials

“…DM containing DNC interactions generally have fast and rapid reversibility under ambient conditions. [ 18,22–24 ] Polymers containing DCBs give relatively slower or even no exchange at ambient temperature, but they are stable and can be activated to exchange under external stimuli. [ 10–13,25–27 ] The major limitation of the materials that have one species of dynamic bonds is their susceptibility toward creep and deformation over time under load or loss of dynamic response without external stimulus.…”

Nanostructured and Advanced Designs from Biomass and Mineral Residues: Multifunctional Biopolymer Hydrogels and Hybrid Films Reinforced with Exfoliated Mica Nanosheets

“…It has been reported that nanoparticles can be used as physical cross-linkers for the formation of hydrogels based on polysaccharides, such as cellulose. 54,55 This cross-linking is mediated via polymer− particle interactions, ionic bonds, and hydrogen bonds. Here, the negatively charged mica nanosheets can be linked with cationic chitin via electrostatic interactions.…”