SCANNING FORCE MICROSCOPY AND POLYMERIZATION STUDIES ON CAST THIN-FILMS OF HECTORITE AND MONTMORILLONITE

Thin films of the smectite clays Na+ exchanged montmorillonite, Ca2+ e xchanged montmorillonite, Na2+ and Cu2+ exchanged hectorite, Cu2+ exch anged sintered hectorite, and Cu2+ and Na2+ exchanged hectorite expose d to benzene, aniline, and thiophene were studied using the techniques of scanning force microscopy (SFM), electron spin resonance (ESR), an d x-ray diffraction. The microstructure of the two montmorillonite cla ys was markedly different, with the Ca-montmorillonite exhibiting a st urdy, close packed array of crystallites of average dimension 0.4 mu m . The Na-montmorillonite clays consisted of smaller (0.1 mu m), more p oorly defined crystallites with an overall cauliflowerlike appearance. The pure Na-hectorite and Cu-hectorite clays exhibited large flat reg ions composed on interlocking platelets. Heat sintering as well as exp osure to benzene resulted in measurable shifts in the platelets perpen dicular to the surface for the Cu-hectorite. It is proposed that in th e sintered case these shifts are due to interlayer water loss accompan ied by Cu reactions, while in the benzene case interlayer benzene poly merization causes inhomogeneous vertical expansion of the clay. Exposu re of Cu-hectorite films to both aniline and thiophene results in larg e-scale polymerization of these monomers. The microstructure of both o f these polymers is similar to that observed in electrochemically prep ared films on Pt substrates. Na-hectorite samples did not exhibit surf ace polymerization upon thiophene, aniline, or benzene exposure. (C) 1 996 American Vacuum Society.