Structure and Conductivity of Semiconducting Polymer Hydrogels

Area of Science:

• Materials Science
• Polymer Chemistry
• Nanotechnology

Background:

• Poly(fluorene-alt-thiophene) (PFT) is a conjugated polyelectrolyte.
• PFT self-assembles into rod-like micelles in aqueous solutions.
• PFT forms hydrogels at modest concentrations (~10 mg/mL).

Purpose of the Study:

• To understand the structure and intermolecular interactions within PFT hydrogel networks.
• To investigate the effect of tetrahydrofuran (THF) on PFT hydrogel structure and properties.
• To explore the role of bridging polymer chains in PFT hydrogel network formation.

Main Methods:

• Cryo electron microscopy for visualizing network structure.
• Oscillatory rheology to study gel network connectivity.
• Small-angle X-ray scattering (SAXS) with Dammin bead modeling.
• Time-resolved microwave conductivity measurements.

Main Results:

• PFT hydrogels exhibit a network structure visualized by cryo-electron microscopy.
• Rheology and SAXS data support polymer chains bridging between PFT micelles.
• Tetrahydrofuran (THF) treatment initially disrupts connections but annealing strengthens the gel network.
• Small oligomers weaken the hydrogel by passivating bridging chains.
• THF annealing increases carrier mobility in dried PFT gels, indicating enhanced connectivity.

Conclusions:

• PFT hydrogels rely on bridging polymer chains for network integrity.
• THF annealing offers a method to enhance PFT hydrogel interconnectedness and conductivity.
• Understanding these interactions is key for designing advanced conjugated polyelectrolyte materials.