Pore volume fraction polymer fractionation modeling

FIG U RE 4.10 Stability diagram showing the stable state of operation of the CCL as a function of the pore volume fraction of secondary pores, Xm, and jq. (Reprinted from Electmchim. Acta, 53(13), Liu, J., and Eikerling, M. Model of cathode catalyst layers for polymer electrolyte fuel cells The role of porous structure and water accumulation. 4435 1446. Copyright (2008), Elsevier. With permission.)... 

Numerous models have been proposed to interpret pore diffusion through polymer networks. The most successful and most widely used model has been that of Yasuda and coworkers [191,192], This theory has its roots in the free volume theory of Cohen and Turnbull [193] for the diffusion of hard spheres in a liquid. According to Yasuda and coworkers, the diffusion coefficient is proportional to exp(-Vj/Vf), where Vs is the characteristic volume of the solute and Vf is the free volume within the gel. Since Vf is assumed to be linearly related to the volume fraction of solvent inside the gel, the following expression is derived ... 

The model domain is a unit cell that contains a single pore, as shown schematically in Figure 2.19. The dimensionless microscopic swelling variable of the unit cell model is given by rj = Vp/vo, where Vp is the volume of the cylindrical pore and vq is the volume of the unit cell under dry conditions. The polymer volume fraction per unit cell is given by [Pg.104]

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