Multiple relaxation modes in associative polymer networks with varying connectivity

Area of Science:

• Polymer Science
• Soft Matter Physics
• Materials Science

Background:

• Network connectivity critically influences the mechanical properties and dynamics of polymer networks.
• Transient polymer networks, formed by reversible cross-links, exhibit unique viscoelastic behaviors.
• Understanding the relationship between connectivity and dynamics is crucial for designing advanced materials.

Purpose of the Study:

• To investigate the impact of systematically reduced network connectivity on the local dynamics of transient polymer networks.
• To characterize the relaxation dynamics and mechanical properties of these networks as a function of cross-link density.
• To elucidate the microscopic mechanisms governing relaxation in weakly interconnected polymer systems.

Main Methods:

• Preparation of transient polymer networks using hydrophobically modified polyethylene glycol chains.
• Systematic reduction of network connectivity by incorporating monofunctionalized chains.
• Characterization of network properties using bulk rheology and dynamic light scattering (DLS).

Main Results:

• Reduced network connectivity significantly decreases elasticity and shortens relaxation times.
• DLS reveals three distinct relaxation modes: a fast cage diffusion, a connectivity-dependent viscoelastic mode, and slow cluster diffusion.
• The intermediate viscoelastic mode, attributed to local connectivity fluctuations, showed surprising independence from the scattering vector (q).

Conclusions:

• Network connectivity is a key determinant of mechanical properties and relaxation dynamics in transient polymer networks.
• Microscopic dynamics, including cage diffusion, local connectivity fluctuations, and cluster diffusion, contribute to the overall viscoelastic response.
• These findings provide fundamental insights into the behavior of weakly interconnected soft materials.