our research team has synthesized silylated MMT from MMT. XRD graphs show the diffraction angle decreases from 6.5 degree (for MMT) to 2 degree due to increase in gallery space. But when polymer (PVA )grafted to Silylated MMT and prepared PVA-silylated MMT nanoCOMPOSITE (1%), 2teta angle was moved to 4 degree. why interlayer space has decreased?
The d-spacing of the clay depends on the amount of the surfactant and its orientation in the silicate gallaries. If you used excess amount of surfactant, the widely opened d-spacing can be reduced upon polymer intercalation by polymer molecules pushing out the surfactant while polymer chains takes pancake-like shape confined by the silicate walls. In this case, the d-spacing reduction can be observed. For more details, see the following papers.
1. "A Differential Scanning Calorimetry Study of the Assembly of Hexadecylamine Molecules in the Nanoscale Confined Space of Silicate Galleries," Y.Q. Li and H. Ishida, Polym. Mat. Sci. Eng., ACS, 85, 562 (2001), and Chem. Mat., 14, 1398 (2002).
2. “Concentration Dependent Conformation of Alkyl Tail in the Nanoconfined Space:: Hexadecylamine in the Silicate Galleries,” Y.Q. Li and H. Ishida, Langmuir,19, 2479-2484 (2003).
3. “Solution Intercalation of Polystyrene and the Comparison with Poly(ethyl methacrylate),” Y.Q. Li and H. Ishida, Polymer, 44, 6571 (2003).
4. “A Study of Morphology and Intercalation Kinetics of Polystyrene-Organoclay Nanocomposites,” Y.Q. Li and H. Ishida, Macromolecules,38, 6513 (2005)
Silylation of MMT may happen more on clay layer edges instead of intragallery. More clay hydroxyl groups on edges than intragallery. (i)When PVA is grafted to edges of clay layers, intercalation by PVA molecules becomes less chances. (ii)During grafting unreacted surfactants might come out of intragallery.
These two reasons might be behind.
The low two-theta indicates very high interlayer spacing in the MMT composite. PVA may be acting as a plasticizer and soften the structure and thus inducing more dense packing.
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