2.6.4. Water Uptake and Swelling Ratio

Water uptake is important for the ion exchange membrane because it provides hydrophilicity of the membrane. Transportation of ions takes place mostly through the bound water inside the membrane by a hopping mechanism.

Water uptake was mainly calculated by the following equation

where Wet_w is the weight of the wet membrane and Dry_w is the weight of the dry membrane.

Hydration number was also calculated by using following equation, where λ is the number of water molecules attached per functional group attached to the polymer backbone, WU is the water uptake, and IEC is the ion exchange capacity (meq. g⁻¹).

Moreover, the swelling ratio was calculated from Equation (4):

where L_s is the length of the wet sample and L_d is the length of the dry sample, respectively.