Scanning force microscopy and polymerization studies on cast thin films of hectorite and montmorillonite

Abstract

Thin films of the smectite clays Na+ exchanged montmorillonite, Ca2+ exchanged montmorillonite, Na2+ and Cu2+ exchanged hectorite, Cu2+ exchanged sintered hectorite, and Cu2+ and Na2+ exchanged hectorite exposed to benzene, aniline, and thiophene were studied using the techniques of scanning force microscopy (SFM), electron spin resonance (ESR), and x-ray diffraction. The microstructure of the two montmorillonite clays was markedly different, with the Ca-montmorillonite exhibiting a sturdy, close packed array of crystallites of average dimension 0.4 μm. The Na-montmorillonite clays consisted of smaller (0.1 μm), more poorly defined crystallites with an overall cauliflowerlike appearance. The pure Na-hectorite and Cu-hectorite clays exhibited large flat regions composed on interlocking platelets. Heat sintering as well as exposure to benzene resulted in measurable shifts in the platelets perpendicular to the surface for the Cu-hectorite. It is proposed that in the sintered case these shifts are due to interlayer water loss accompanied by Cu reactions, while in the benzene case interlayer benzene polymerization causes inhomogeneous vertical expansion of the clay. Exposure of Cu-hectorite films to both aniline and thiophene results in large-scale polymerization of these monomers. The microstructure of both of these polymers is similar to that observed in electrochemically prepared films on Pt substrates. Na-hectorite samples did not exhibit surface polymerization upon thiophene, aniline, or benzene exposure.