Effect of Surface Alignment on Connectivity in Phosphonium-Containing Diblock Copolymer Anion Exchange Membranes

The performance of ion exchange membranes in fuel cells is critically linked to its ion-conducting morphology. In this report, we analyzed the connectivity of anion exchange membranes (AEMs) by electrostatic force microscopy (EFM). As a tapping-mode AFM based technique, EFM probes height, phase, and electrostatic force gradient imagines through two-pass interleave scans, which reveals the direct relationship between membrane surface morphology and connectivity of the ionic domain. The AEMs are diblock copolymers of a polyisoprene (PIp) block and a polystyrenic block containing phosphonium ion (P(R3P+)MS). Different alignments of cylinders were observed in bulk, and on surface for AEMs with different ion exchange capacity (IEC) and preparation methods. The impacts of the cylinder alignment on the connectivity of the ionic domain were then investigated by EFM. For AEM 13 with parallel aligned cylinders on the surface, many disconnected regions were observed throughout the membrane. In contrast, the perpendi...