Adsorption, NMR, and thermally stimulated depolarization current methods for comparative analysis of heterogeneous...

Structural characterization of different silicas (ordered mesoporous silicas MCM-41, MCM-48, and SBA-15, amorphous silica gels Si-40, Si-60, and Si-100, and initial and wetted-dried fumed silica A-300) and bio-objects (fibrinogen solution, yeast cells, wheat seeds, and bone tissues) has been done using two versions of cryoporometry based on integral Gibbs-Thomson (IGT) equation for freezing point depression of pore liquids measured by 1H NMR spectroscopy (180-200 < T < 273 K) and thermally stimulated depolarization current (TSDC) method (90 < T < 273 K). The IGT equation was solved using a self-consisting regularization procedure including the maximum entropy principle applied to the distribution function of pore size (PSD). Comparison of the PSDs calculated by using the cryoporometry and nitrogen adsorption methods for the mentioned silicas demonstrates that IGT equation provides satisfactory fit which is better than that obtained with nonintegral Gibbs-Thomson (GT) equation (based on the GT equation) proposed by Aksnes and Kimtys. The NMR- and TSDC-cryoporometry methods applied to probe biosystems give clear pictures of changes in the structural characteristics caused, e.g., by hydration and swelling of wheat seeds and yeast cells, coagulation and interaction of fibrinogen with solid nanoparticles in the aqueous media, and human bone tissue disease.