Exfoliation adsorption process

Epoxy-clay nanocomposites were studied extensively, but only ordered exfoliated nanocomposites were reported with in situ polymerization. Two recent works showed that disordered and highly exfoliated epoxy-clay nanocomposites can be prepared using an exfoliation-adsorption process." In this method the organo-modified clay is first dispersed in a solvent. It is well known that due to the weak forces that stack the layers together, layered silicates can easily be swelled and eventually delaminated in an adequate solvent. The polymer then adsorbs onto the delaminated sheets, and when the solvent is evaporated, a highly disordered structure is obtained before starting the standard in situ polymerization. 

FIGURE 9.6 XRD pattern of a clay-epoxy system (epoxy/DM-clay) before and after curing prepared by the exfoliation-adsorption process, and for comparison, bis(2-hydrox-yethyl)methyl tallow alkylammonium-modified MMT (Epoxy/clay-30B). (From Ref. 43, copyright 2004, American Chemical Society, with permission.)... 

Epoxy-clay nanocomposites are prepared by in situ polymerization with organo-modified clays. In this technique, the prepolymer intercalates between the layered crystals during swelling, a process in which heat, stirring, and/or sonication is applied to favor prepolymer diffusion into the clay gallery. Then polymerization can be initiated between the intercalated sheets either by heat, radiation, or a suitable initiator. A variant of in situ polymerization is the exfoliation-adsorption technique, in which the organo-modified clay is first dispersed in a solvent before starting the standard in situ polymerization. 

The four main strategic processes for preparing polymer/layered silicate nanocomposites are exfoliation-adsorption, in situ intercalative polymerization, melt intercalation and template synthesis. ... 

A systematic study of krypton adsorption on exfoliated graphite was subsequently undertaken by Thorny and co-workers (Thorny and Duval, 1969 Thorny et al., 1972). Their stepwise isotherm, determined at 77.3 K, is shown in Figure 4.1. The layer-by-layer nature of the physisorption process is clearly evident - at least up to four molecular layers. This isotherm shape is remarkably similar to that of the krypton isotherm on graphitized carbon black reported by Amberg et al., (1955). 

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