2.4. Water Uptake

Water uptake (WU) is commonly used to characterize ion exchange materials. It was measured for the ionomer coating of the hierarchical membranes. For the composite material WU of the ionomer needs to be distinguished from water absorption into the pores of the substrate. The objective of the characterization measurement was to identify the impact of the composition of the ionomer coating on its water uptake.

To obtain samples of the coating material free of the porous substrate the coating formulations were casted and cured on a PTFE sheet, then delaminated to obtain flakes. The samples were soaked in deionized water for 24 h to ensure full hydration. After removing the excess water using absorbent paper, the fragile samples were weighted to obtain the wet weight (W_w). Subsequently they were dried in an oven at 70 °C for at least 24 h and weighted again to obtain the dry weight (W_D). The water uptake was calculated according to Equation (1):

where W_W and W_D is the weight of wet and dry ion exchange layer.