Telechelic Polymer Hydrogels: Relation between the Microscopic Dynamics and Macroscopic Viscoelastic Response.

Area of Science:

• Polymer Science
• Materials Science
• Soft Matter Physics

Background:

• Telechelic polymers, featuring hydrophilic chains with hydrophobic end-groups, self-assemble into hydrogels through interconnected micelles.
• Understanding the relationship between microscopic dynamics and macroscopic rheological properties is crucial for designing advanced materials.

Purpose of the Study:

• To quantitatively correlate the chain exchange kinetics of telechelic polymer hydrogels with their rheological properties.
• To elucidate the role of molecular dynamics in determining hydrogel connectivity and mechanical response.

Main Methods:

• Utilized time-resolved small-angle neutron scattering (TR-SANS) to measure chain exchange kinetics.
• Employed linear oscillatory shear measurements to assess the mechanical response (rheology).
• Integrated TR-SANS and rheological data to establish quantitative relationships.

Main Results:

• A direct correlation was found between the characteristic relaxation time from rheology and TR-SANS at intermediate concentrations.
• Activation energy (Ea) for debridging was concentration-independent and consistent between TR-SANS and rheology.
• A discrete change in activation energy was observed at the melting point, indicating the influence of fusion enthalpy.

Conclusions:

• Hydrogel mechanical properties and connectivity are governed by molecular exchange processes.
• At low concentrations, faster relaxation in rheology compared to TR-SANS is attributed to entropic forces from bridging chain deformation.