Expansion characteristics of organoclay as a precursor to nanocomposites

Smectite that has reacted for 48 h with hexadecyltrimethylammonium (HDTMA) cations equivalent to 1.0 and 2.5 times the cation exchange capacity (CEC) converts to HDTMA-smectite. The microstructure of this organoclay is observed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). When the Na cations in the interlayer of clay are exchanged with HDTMA ions, the change in internal external surface configuration is augmented by the intercalation of organic cations. The HRTEM image of the HDTMA-treated smectite (1.0 CEC) reveals stacks of slightly curved layers with an average basal spacing of 20–24 Å. In such organoclay, the repetitive multilayer structure is well preserved, but as the loading amounts of HDTMA increase to 2.5 CEC, a peculiar expansion is observed in some silicate layers. The HDTMA-exchanged smectite shows not only morphological features such as the irregular, wavy surface with curled edges, but also structural features such as large d-spacings (>40 Å) and lattice distortion. Such morphological characteristics seem to be related to the intercalation amounts of HDTMA cations into the interlayer of smectite. A close examination of almost any layer reveals a continuously variable spacing, and this seems to be due to a different interlayer charge. Some exfoliated layers or edges may be locally developed on the low charge interlayer regions by the sufficient adsorption of organic surfactants beyond the CEC due to the tendency of alkyl chain interaction.