Surlyn/metal oxide nanocomposites: Formation, morphology, and interactions of inorganic and organic phases
The goal of this research was to produce Surlyn® /metal oxide composite materials, examine the morphology of the resulting inorganic phase, and the interactions between the two phases. Effects of counter-ion type and degree of neutralization on inorganic uptake were studied. The Na+ neutralized materials were found to give the highest and fastest silicate uptakes, while for the titanate materials the un-neutralized materials gave the highest uptakes. Morphology of the resulting composites was studied using TEM, tapping mode AFM, and ESEM/EDS. Counter-ion type was found to influence the size and distribution of the inorganic phase, which exists as discrete nanosized particles. TEM micrographs and tapping mode AFM phase images of the Surlyn ® /silicate composites suggest uniformly spaced non-aggregating particles. The concentration of the inorganic phase is not uniform throughout the composite. Bimodal distributions are found, with high inorganic concentrations near the surfaces of the composite films. Particle number density varies with film depth. More particles are found near the surface regions than at the core of the films. Evidence suggests that particle size distribution varies with counter-ion type. Un-neutralized materials show broader size distributions than the Zn +2 and Na+ neutralized composites. The Na+ neutralized Surlyn® /silicate composites show the smallest particle sizes and narrowest size distribution. Transmission electron micrographs of the Surlyn® /titanate composites do not show evidence of an inorganic phase. Tapping mode AFM phase images show the presence of discrete nanosized particles. ESEM/EDS experiments find large concentrations of titanium near the surface, and limited incorporation at the center of the films. EXAFS spectroscopy of Zn+2 neutralized Surlyn® /silicate composites suggests coordination of water at the edges of the ionic aggregates. Infrared spectroscopy finds new peaks due to the inorganic phase. The un-neutralized Surlyn® /silicate composite materials do not show evidence of interactions between the phases. IR spectra of the neutralized Surlyn® /silicate composites show subtle changes in the range from 1500 cm-1 to 1800 cm-1 . The Surlyn® /titanate ATR-FTIR spectroscopy experiments show changes in the carboxylate and carbonyl stretching regions, indicating a neutralization of carboxylic acid groups with titanium counter-ions.