Ordered structures in proton conducting membranes from supramolecular liquid crystal polymers

Area of Science:

• Polymer Science
• Materials Science
• Electrochemistry

Background:

• Poly(p-phenylene terephthalamide) (PPTA) is a high-performance polymer.
• Sulfonation enhances water solubility and ionic conductivity in polymers.
• Fuel cell membranes require efficient proton transport and stability.

Purpose of the Study:

• To synthesize and characterize highly sulfonated PPTA derivatives.
• To investigate the effect of molecular configuration on polymer properties.
• To evaluate the potential of these sulfonated PPTA films for fuel cell applications.

Main Methods:

• Preparation of three sulfonated PPTA forms: S-PPTA, S-invert-PPTA, and S2-PPTA.
• Film casting from solution for S-PPTA and S-invert-PPTA.
• Water absorption, conductivity, X-ray diffraction, and SEM analysis.

Main Results:

• S-PPTA and S-invert-PPTA films exhibit varying water absorption and conductivity, comparable to Nafion.
• Proton mobility is more restricted in these sulfonated PPTA films compared to Nafion.
• X-ray diffraction reveals distinct molecular alignments (homeotropic for S-PPTA, planar for S-invert-PPTA).
• SEM analysis shows layering consistent with polymer chain alignment.

Conclusions:

• The molecular configuration significantly impacts the properties of sulfonated PPTA films.
• The observed polymer alignment offers potential for enhancing proton transport.
• These sulfonated PPTA films are promising candidates for next-generation fuel cell membranes.