TOPOLOGICAL AND THERMAL-PROPERTIES OF SURFACTANT-MODIFIED CLINOPTILOLITE STUDIED BY TAPPING-MODE(TM) ATOMIC-FORCE MICROSCOPY AND HIGH-RESOLUTION THERMOGRAVIMETRIC ANALYSIS

Unmodified and surfactant-modified clinoptilolite-rich tuff (referred to here as ''clinoptilolite'') and muscovite mica were examined with t apping-mode atomic force microscopy (TMAFM) and high-resolution thermo gravimetric analysis (HR-TGA) in order to elucidate patterns of hexade cyltrimethylammonium bromide (HDTMA) sorption on the treated surface a nd to understand the mechanisms of this sorption. TMAFM images were ob tained to a scale of 50 nm by 50 nm. The images of unmodified clinopti lolite showed a framework pattern on the ac plane, comparable to previ ously reported images. Images of modified clinoptilolite at 12.5% and 25% of external cation exchange capacity (ECEC) coverage by HDTMA show ed evidence of the HDTMA molecules arranged as elongated, topographica lly raised features on the ne plane. At 50% HDTMA coverage, the images contained what appeared to be agglomerations of surfactant tail group s. The z-direction thickness of the raised features on the 12.5% cover age sample corresponded to the thickness of the carbon chain of the su rfactant tail-group (0.4 nm), whereas the z-thickness on the 25% cover age sample was between 0.4 and 0.8 nm, indicating crossing of doubling of tail groups. Repulsive forces between the modified clinoptilolite and the silicon TMAFM probe increased with increasing HDTMA coverage. HR-TGA showed a 100 degrees C increase in HDTMA pyrolysis temperatures at coverages of less than 50%, probably due to an increased stabiliza tion of the HDTMA due to direct tail interactions with the clinoptilol ite surface at lower coverages versus smaller stabilization due to sur factant tail-tail interactions at higher coverages. Our results indica te that buildup of HDTMA admicelles or some form of a bilayer begins b efore full monolayer coverage is complete.