Structure and Dynamics of the Exfoliation of Layered Nanosilicates in 'Liquid Rubber'
Final Report Abstract
In this project, investigations of organically modified clays hydroxyl- or carboxyl-end terminated low molecular weight polybutadiene composites have been tested regarding their gelation properties and mechanism. Organo-laponite was observed not to form a gel at all, independent on the applied polybutadiene matrix and its chain-ends. Therefore, organically modified montmorillonite was used for further studies. In order to test the house-of-cards structure theory, edge-modified organo-clays were produced. However, the results of these experiments were indifferent. Nevertheless, when changing the number of ‘sticky’ hydroxyl- or carboxyl-groups at the polybutadiene chain, it was found, that even one single group per chain is enough to let the organo-montmorillonite exfoliate at 80°C. Finding gelation for these single modified chains, disproves that the gelation is caused by bridging the clay sheets with sticky telechelic polybutadiene chains. Furthermore, comparing several commercial organo-montmorillonites showed only differences by the type of surfactant, but not the mining location of the clay. Therefore, catalytic reactions by possibly included metals like iron can be excluded. Heating these composites of ‘sticky’ polybutadiene and organo-montmorillonite up to 80 °C (at the temperature where the maximal gelling rate is reached), a subsequent disappearing of the tactoids within the tactoid aggregates is monitored, that is followed by an exfoliation process of the individual tactoids which are associated with the former aggregate grains. Nevertheless, during this process gelation occurs and still needs to be characterized by methods focusing on dimensions below microscopic scale.
