Adsorption and Sorption Experiments

Nitrogen adsorption is often a very powerful characterization for the pore structure of particles and membranes. However, dne to the distribution of ultra-micropoies with narrow pore size distribution, sorption at -196°C becomes unpractical because of extremely slow adsorption rate [13]. The adsorption of supercritical gases seems to be more appropriate to characterize the CMSM pore stractures for the following reasons. (1) Snpercritical adsorption in micropotes is faster than sub-critical adsorption. (2) Snpercritical adsorption takes place mostly in micropores while sub-critical adsorption may occm even on the outer surface of the membrane. 

A CMSM (referred to as KP800) was prepared by Nguyen et al. via the controlled pyrolysis of Kapton PI film nnder vacuum. The highest pyrolysis temperature was 800°C. The membrane showed reasonable sieving effect for gas molecules with different kinetic diameters. 

Adsorption desorption isotherms of nitrogen at three temperatures are shown in Fig. 6.21. There is no hysteresis, indicating no capillary condensation due to the absence of mesopores, since the temperature is above supercritical temperature. Data were analyzed by the model proposed by Nguyen and Do [14]. The fitted results are presented in Fig. 6.22a-c, in which pressure is given in normal and logarithmic scale. A narrow pore size distribution is shown in Fig. 6.22c. The majorily of the 

14 HRTEM images (scale bar represents 12 nm)ofSNPCM-ll showing (a) a typical amorphous region, and (b) a nanostructured region with EDX analysis (insert). (From [10]) 

Another example of using the adsorption of supercritical fluid for the characterization of CMSM is the work done by Katsaros et al. [15]. It was attempted to 

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