Phenomenological methanol sorption model for Nafion® 117

A thermodynamic model is developed to describe methanol sorption phenomena in proton exchange membranes (PEMs). The methanol sorption in the model is determined by the swelling pressure caused within the membrane as a result of stretching of the polymer chains upon methanol sorption. The stretching of the polymer chains is expressed in terms of spring constant κ. The swelling pressure exerted within the pores of the membrane is assumed to be linear in solvent uptake. Furthermore, the methanol molecules in the membrane are divided into those that are chemically, or strongly, bound to the acid sites, λiC, and others that are free to physically equilibrate between the fluid and the membrane phases, λiF. The sorption model can predict the complete isotherm due to methanol vapor sorption by the membrane.