Exfoliation probing

High-resolution TEM only probes a very small volume, which may or may not be representative of the total composite. Moreover sample preparation for TEM analysis is difficult and time-consuming. Therefore, the method is too costly for routine characterization of nanoeomposites. As a result researchers are now using melt rheology as a complementary method to analyse the dis-persion/exfoliation in polymer lay nanoeomposites. Several authors found that the shear thinning index, n, gives a semi-quantitative measure of the degree of exfoliation. 

Maupin, P.H. Gilman, J.W. Harris, R.H. Bellayer, S. Bur, A.J. Roth, S.C. Murariu, M. Morgan, A.B. Harris, J.D. Optical probes for monitoring intercalation and exfoliation in melt-processed polymer nanocomposites. Macromol. Rapid Commun. 2004, 25, 788-792. 

X-ray diffraction (XRD), is commonly used to probe the nanocomposite structure. However, XRD can only detect the periodically stacked clay layers, disordered or exfoliated layers are undetected. In general, in layered silicate-filled polymers a coexistence of exfoliated, intercalated and disordered layers is observed. 

Subambient thermal volatilization analysis can also be used to probe the effects of physical fillers in silicone materials. In 2008 Lewicki et al. [51] studied the degradation profiles and product speciation of a series of montmorillonite clay filled silicone elastomers which had been characterized using SATVA. Shown in Figure 13.17 are a series of TVA thermal degradation profiles for the non-oxidative degradation of a bimodal-condensation-cured silicone matrix, filled with 0-8 wt% of organically modified montmorillonite (0-MMT) exfoliated nanoclay platelets. 

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