Liquid Crystal Sulfonated Aramids as Proton Exchange Membranes for Fuel Cell Applications

Liquid Crystal Sulfonated Aramids as Proton Exchange Membranes for Fuel Cell Applications

Gao, J.

Dingemans, T.J. (promotor)
Picken, S.J. (promotor)

Aerospace Engineering

Aerospace Structures and Materials

2015-09-04

Two sulfonated aramids, poly(2,2’-disulfonylbenzidine terephthalamide) (PBDT) and poly(2,2’-disulfonylbenzidine isophthalamide) (PBDI) were synthesized with the aim to explore their unique morphology for proton exchange membrane applications. Due to the different polymer structures, PBDT forms a nematic liquid crystal, whereas PBDI is isotropic. Both polymers show excellent thermal stabilities (Td5% > 400 oC), high storage moduli (E’ = 3 – 15 GPa) and crosslinked films are flexible and easy to handle. Pulsed-field-gradient NMR diffusometry reveals that the in-plane water diffusion in the nematic PBDT membrane is as high as 3.3x10-10 m2/s, whereas the diffusion in amorphous PBDI is only 2.5x10-10 m2/s. Whereas neat and crosslinked PBDI shows isotropic diffusion, neat PBDT shows a high diffusion anisotropy (D?/D? = 3.0), which increases as a function of crosslink density (D?/D? = 4.6 at 80% crosslinking). This diffusion anisotropy is substantially higher than that typically observed for low molecular weight liquid crystals and for oriented polymeric conductors such as Nafion® (D?/D? ~ 2.0). The nematic order in the PBDT membrane also promotes directed ionic conductivity, i.e. Na+ conductivity in PBDT is 2.24 x 10-2 S/cm and 1.67 x 10-2 S/cm for PBDI, respectively. We propose that the rigid-rod PBDT chains form nano-scale hydrophilic channels, which act as pathways for transporting water molecules and ions.

liquid crystal polymers
sulfonated aramids
ionic crosslinking
ion transport
ordered structure
NMR diffusion

https://doi.org/10.4233/uuid:0d11b27b-9b6d-47a6-891c-a32408409b37

978-94-6259-824-9

Institutional Repository

doctoral thesis

(c) 2015 Gao, J.