Viscoelasticity and Sol-Gel Transition via Multiscale Self-Assembled Nanostructures in Short-Side-Chain PFSA...

Area of Science:

• Materials Science
• Polymer Chemistry
• Electrochemistry

Background:

• High-temperature proton exchange membranes (PEMs) are crucial for fuel cell technology.
• The properties of PEMs are dictated by the polymer's structure in dispersion during fabrication.
• Short-side-chain perfluorosulfonic acid (SSC-PFSA) is a key material for advanced PEMs.

Purpose of the Study:

• To investigate the concentration-dependent viscoelasticity and microstructure of SSC-PFSA dispersions.
• To elucidate the multiscale self-assembly mechanism leading to gelation and membrane formation.
• To establish fundamental connections between polymer morphology and the physical properties of SSC-PFSA electrolyte membranes.

Main Methods:

• Rheological analysis to study viscoelastic properties.
• Cryo-transmission electron microscopy (Cryo-TEM) for microstructural visualization.
• Small-angle X-ray scattering (SAXS) for structural characterization across multiple length scales.

Main Results:

• SSC-PFSA forms rod-like primary aggregates with a scaling exponent deviating from theoretical predictions.
• Primary aggregates assemble into secondary aggregates, leading to deviations in viscosity-concentration relationships.
• Further concentration increases result in secondary aggregate percolation and gelation, forming a network structure.

Conclusions:

• A novel multiscale self-assembly mechanism governs the gelation of SSC-PFSA dispersions.
• This mechanism explains the evolution of nonequilibrium morphology from dilute solutions to gel networks.
• Understanding this process is vital for optimizing the physical properties of SSC-PFSA electrolyte membranes for high-temperature applications.