Porod constant

Recently, a unique approach for using the correlation fiinction method has been demonstrated to extract morphological variables in crystalline polymers from time-resolved syncluotron SAXS data. The principle of the calculation is based on two alternative expressions of Porod s law using the fonu of interference fiinction [33. 36]. This approach enables a continuous estimate of the Porod constant, corrections for liquid scattering... 

The Porod constant K can be used to determine the specific surface area Shn either by applying the invariant Q or directly from the experimentally derived scattering cross-section when no micropores are present the following relations hold ... 

Here, Vo is the total volume of the sample, ps is the density of the solid phase, (f) is the porosity of the sample, Apsuo is the difference in coherent scattering length density between the solid and the pore phase, and Cn, Cx are the factors to be applied in case of neutrrMi and X-ray scattering, respectively (Table 21.2). When two Porod regimes are present [as it is the case for microporous samples (see Figure 21.15)] both can be evaluated according to (21.13 a, b). Hereby care has to be taken to correctly match the Porod constants with the respective densities of the sohd phase and the surface area that can be extracted. ... 

Porod constant from the Q part in the cross-section... 

The quantity/], arises from density fluctuations and Kp is the Porod constant Note the strong positive deviation in the Porod plot (f(q)q versus q ) illustrated as an inset to Figure 2. Positive deviations from Porod s law are caused by thermal density fluctuations [6]. A regression analysis of tiie linear part of the curve gives values of = 0.0S and = 356. A most be subtracted from the raw intensity data before both dj and the invariant are calculated. 

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