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 (δh) showed little suspended MMT, but liquids with moderate or poor hydrogen-bonding groups precipitated MMT completely, this indicates that δh is an important factor for the dispersion state of natural MMT in a liquid. The basal spacing expansion also depends on polar components (δp) and hydrogen-bonding components (δh) of organic liquids. Liquids with high δh values showed expansion in the order of methyl alcohol > ethyl alcohol > 2-propyl alcohol > n-hexane > toluene > benzene, and monomers with high δp values exhibited expansion in the order of n-butyl acrylate > acrylonitrile > methyl methacrylate > styrene. Because dipole−dipole interactions involved both δh and δp, 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.