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