Acid-base behavior 586 INDEX

Another interesting use of empirical AN and DN indexes obtained by the method of refs.30,35 is exemplified in Table 3. This reports the temperature dependence of acid/base interactions in two commodity polymers, PVC and PC. The relevant AN and DN parameters for these polymers were evaluated by IGC at temperatures ranging from 30 - 130 C. As expected, at room temperature PVC again classifies as acid, and the relative acidity of the polymer surface increases steadily from 30 to about 70 C. Above 80 -90 C, however, the trend is reversed and acid/base interaction forces diminish. PC behaves as an amphoteric solid, its AN and DN finite and roughly equal at room temperatures. Above about 60 C however, the relative behavior of the polymer is that of a Lewis base. The results may be rationalized as follows ... 

Treatment of buffer efficiency in general is not limited to examination of various monoprotic and polyprotic acids, but rather to the behavior of mixtures of acids. Further, from plots of buffer index vs. pH, it is easy to see that strong acids and bases are reasonable buffers for the extreme (low and high) Ph ranges. This leads to the definition of a buffer as a solution that has neutralization capacity, rather the more limited but commonly used definition as a mixture of a weak acid and its conjugate base (See Figure 8.5). 

Studies have demonstrated that the chemical composition of calculi can be partially determined by CT in vitro, but this differentiation is more complicated and less reliable in vivo (Hillmand et al. 1984 Mostafavi et al. 1998 Nakada et al. 2000 Alkadhi et al. 2007). Using DECT, the chemical characterization of stones is possible based on their characteristic DE index. DE postprocessing software algorithms assume a mixture of water, calcium, and uric acid for every voxel and color codes voxels that show a DE behavior similar to calcium in blue and one that is similar to uric acid in red (Fig. 36.4). Voxels that show a hnear density behavior at... 

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