Formation of poly(methylmethacrylate) layers on the surface and intergallery regions of Cu 2+-, Fe 3+-, and VO 2+-exchanged hectorite thin films

Abstract

We have used the techniques of scanning force microscopy (SFM), electron spin resonance (ESR) spectroscopy, ATR IR spectrometry, and powder X-ray diffraction (XRD) to investigate the reaction of methylmethacrylate (MMA) on metal cation-exchanged hectorite thin films. SFM images of the topmost surface of Cu 2+-, VO 2+-, and Fe 3+-exchanged hectorite exposed to liquid MMA show that in all three cases a complete layer of the polymer, polymethylmethacrylate (PMMA), has formed. IR spectra taken on the same films support the SFM observations for the VO 2+ and Fe 3+ samples, but are not conclusive for the Cu 2+-exchanged films. The PMMA formed on the surface of these films is segregated into small grains or bundles, ranging in average size from 250 Å (Cu 2+ hectorite substrate) to several thousand ångström units (Fe 3+ hectorite substrate). XRD and ESR measurements on these thin films indicate that little intercalation of the MMA monomer into the intergallery regions of the Cu 2+-exchanged clay film occurs. This result is substantiated by SFM phase-contrast images of exposed intergallery regions in these samples. For the VO 2+- and Fe 3+-exchanged hectorite films, XRD-measured basal spacings show moderate intercalation of the organic monomer. SFM images of these intergallery regions clearly indicate the presence of interlayer polymer, in the form of quasi-two-dimensional sheets.