Copper-Ion-Assisted Self-Assembly of Silicate Clays in Rod- and Disklike Morphologies

Abstract

Self-assembled rodlike (0.3-2.5 microm in diameter and 5.3-31 microm in length) and disklike microstructures (1.8-10.6 microm in width and 0.1-1.0 microm in thickness) are uniquely present in amorphous clay aggregates. Clay units were prepared by intercalation of Na(+)-montmorillonite (Na(+)-MMT) with copper ions (Cu(2+)) and poly(oxypropylene)-amine salt (POP) in simultaneous or stepwise ionic exchange reactions. Differences in process control during incorporation of Cu(2+) and hydrophobic POP greatly affected the layer structure of the clay units (d spacing of 12-53 A) and consequently their amphiphilic dispersion properties. By controlling the dispersion in water and drying at 80 degrees C, highly ordered self-assembly structures were obtained, presumably as a result of self-piling of clay units in competing vertical and horizontal directions. In general, association with Cu(2+) yielded units with a disklike microstructure, in contrast to the rod-like structure obtained for POP-intercalated clay. The self-assembled structures were characterized using X-ray diffraction, UV adsorption, thermal gravimetric analysis, zeta potential, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques. Control of the clay self-piling process provides a new synthetic route for the fabrication of bottom-up microstructures that are potentially useful for templates, sensors, and electronic devices.