Water Uptake by Pore Ensemble

A spatial dispersion in the distribution of wall charges is accounted for by introducing a density distribution function n ((Tq), defined as the number of pores per infinitesimal interval of gq. Knowledge of n (ao) is a prerequisite for predicting the water sorption behavior of a PEM. The following integral expressions relate n (ao) to the number of unit cells Nuc in a sample of total dry volume Vo  

Pressure equilibrium demands that the liquid pressure, established in the critical pores at jo,c is homogeneous and isotropic. Thus, the same liquid pressure applies in all pores with ao ao,c that have been already filled with water. As a result of the increase in these pores will undergo continuous swelling to attain new equilibrium 

Dry pores with different wall charge density parameters FI 

Homogeneous and isotropic liquid pressure is warranted for high connectivity of the network of water-filled pores. This requirement, which would be indicated experimentally by the absence of hysteresis effects in water absorption/desorption isotherms, is a prerequisite for the proposed mechanism of pore swelling. 

Under equilibration in a saturated vapor atmosphere, a determines the maximal values of radius, swelling parameter and liquid pressure of swollen pores. A typical set of parameters gives= 21 nm, = 105 and P —67 atm. For this case, water sorption from vapor would level off at 0.95. The leveling-off of inte- 

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