Small angle scattering zeolites

Further characterization of the mechanical properties and structures of such zeolite-reinforced PDMS elastomers by Wen and Mark [139] also utilized small-angle neutron scattering (SANS) [141, 143, 214—220] and transmission electron microscopy (TEM). The neutron-scattering profiles of the pure and zeolite-filled PDMS networks were identical, which indicated negligible penetration of the polymer into the zeolite pores. The TEM pictures showed that the zeolite with the larger pore size had a somewhat smaller particle size, and this is probably the origin of its superior reinforcing properties [62, 139]. 

In the past 10 years, many characterization techniques have been used in the in situ study of the formation mechanism of zeolite from clear solution. For example, Honssian et al. studied the TPA-silicalite-1 system by using the small-angle X-ray scattering technique [34] Carlsson et al. performed a modeling study on the crystallization of silicalite-I from a liquid-phase system [35] Smaihi and colleagues applied in situ 27A1-,... 

L.E. Iton, F. Trouw, T.O. Brun, J.E. Epperson, J.W. White, and S J. Henderson, Small-Angle Neutron-Scattering Studies of the Template-Mediated Crystallization of ZSM-5-Type Zeolite. Langmuir, 1992, 8. 1045-1048. 

Small-angle neutron scattering profiles for the PDMS elastomers filled with the two types of zeolite were nearly the same, which argues against chain interpenetration in the large-pore zeolite and not in the small-pore one. Since, statistically, penetration by loops would be much more likely than by ends, it may be necessary to have zeolite pore diameters more than twice the diameter of the potentially-penetrating chain. 

The active surface of a zeolite is internal and intrinsic to the crystal structure. Diffraction techniques can therefore yield direct data on those structural features that control catalytic or sorptive performance. However, zeolite characteristics hamper the effective application of diffraction methods. Zeolite constituents have, generally, low atomic numbers and the normalized scattering power of a zeolite unit cell is relatively small. Zeolites have open firework structures supporting accessible void volumes which can be as much as 50% of the total crystal volume [1-3]. The void spaces are either empty (and hence contributing no scattered intensity to the measured diffraction pattern) or filled with species that are have positional or dynamic disorder and hence contribute to the diffraction peaks almost exclusively at low scattering angles. 

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