Effect of monomers on the basal spacing of sodium montmorillonite and the structures of polymer-clay nanocomposites

The basal spacings of sodium montmorillonite (MMT) dispersed in various solvents and monomers were measured via X-ray diffraction. Some liquids with strong hydrogen-bonding groups (delta(h)) showed little suspended MMT, but liquids with moderate or poor hydrogen-bonding groups precipitated MMT completely, this indicates that delta(h) is an important factor for the dispersion state of natural MMT in a liquid. The basal spacing expansion also depends on polar components (delta(p)) and hydrogen-bonding components (delta(h)) of organic liquids. Liquids with high delta(h) values showed expansion in the order of methyl alcohol > ethyl alcohol > 2-propyl alcohol > n-hexane > toluene > benzene, and monomers with high delta(p) values exhibited expansion in the order of n-butyl acrylate > acrylonitrile > methyl methacrylate > styrene. Because dipole-dipole interactions involved both delta(h) and delta(p), liquid dipole moments were adopted to explain the expansion of MMT in polymer-MMT nanocomposites. Monomers with high dipole moments showed large basal spacings before polymerization and produced exfoliated polymer-MMT nanocomposites, whereas those with low dipole moments showed smaller basal spacings and produced intercalated polymer-MMT nanocomposites.