Standard porosimetry

The experimental basis of sorption studies includes structural data (SANS, SAXS, USAXS), isopiestic vapor sorption isotherms,i and capillary isotherms, measured by the method of standard porosimetry. i 2-i44 Thermodynamic models for water uptake by vapor-equilibrated PEMs have been suggested by various groupThe models account for interfacial energies, elastic energies, and entropic contributions. They usually treat rate constants of interfacial water exchange and of bulk transport of water by diffusion and hydraulic permeation as empirical functions of temperature. 

To begin, it is essential to rationalize the equilibration of water within the membrane at AP = 0, APs = 0, j = 0, and = 0. The suggested scenario of membrane swelling is based on the interplay of capillary forces and polymer elasticity. In order to justify a scenario based on capillary condensation, isopiestic vapor sorption isotherms for Nafioni in Figure 6.9(a) are compared with data on pore size distributions in Figure 6.9(b) obtained by standard porosimetry.i In Figure 6.9(a), a simple fit function. 

The method of standard porosimetry (MSP)41-43 was one of the first approaches used to obtain air-water capillary pressure curves for GDMs.16 In this test, a GDM sample is initially saturated with water and contacted with a water-saturated porous disc, which is a standard with known Pc(Sw) behavior. The capillary pressure of the sample-standard system is varied by allowing the liquid to evaporate from the standard and sample while in contact. If the two media can be assumed to be in capillary equilibrium, their capillary pressures are equal. Saturation is determined by measuring the weights of the sample and standard periodically. The capillary pressure of the system is found by reference to the known capillary pressure curve of the standard. This method is limited to scanning... 

A close set of equations was formulated in Ref. 16, related to the capillary pressure isotherms determined by the method of standard porosimetry [60], In the latter procedure, the equilibrium amount of the wetting liquid is measured in the porous sample under study. Simultaneously, the amount of the wetting liquid is measured in the standard specimen with a genuine porous structure, in which the capillary equilibrium is established. The standards are kept in thermodynamic equilibrium with the sample. The comparison of the amount of wetting liquid in the membrane with the pore-radius distribution in the standards, enables one to record (with a minimum of theoretical assumptions), the volume-size and surface-size distribution curves, specific pore-space surface area, and absorption isotherm in the membrane of interest, for various wetting liquids. 

Y. M. Volfkovich, N. A. Dreiman, O. N. Belyaeva, and I. A. Blinov, Standard-Porosimetry Study of Perfluorinated Cation-Exchange Membranes, Soviet Electrochemistry, 24, 324 (1988). 

Volfkovich YM, Bagotzky VS. The method of standard porosimetry 1. Principles and possibilities. J Power Sources 1994 48 327-38. 

Another method that should be shortly mentioned here is the standard porosimetry developed by Volfkovich. Based on a well-characterized reference material the pore size distribution of a sample can be determined by making use of a capillary equilibrium between the sample and the reference. This variant of porosimetry is very sensitive and, like capillary flow, a non-destructive method. 

The experimental basis of sorption studies includes isopiestic vapor sorption isotherms (Morris and Sun, 1993 Pushpaet al., 1988 Rivin et al., 2001 Zawodzinski et al., 1993c) and capillary isotherms, measured by standard porosimetry (Divisek et al., 1998 Vol fkovich and Bagotsky, 1994 Vol fkovich et al., 1980). A number of thermodynamic models of water uptake by vapor-equilibrated PEMs have been... 

---