Hematite nanoparticle monolayers on mica: Characterization by colloid deposition

Abstract

Colloid particle deposition (also referred to as colloid enhancement, CE) was applied to characterize hematite nanoparticle monolayers on mica. The average size of hematite particles (determined by AFM and dynamic light scattering) was 22nm. The monolayers were produced under diffusion-controlled transport from suspensions of various bulk concentration at pH 3.5, I=10−2M, where the particles exhibited a positive zeta potential of 39mV. The monolayer coverage, quantitatively determined by AFM and SEM, was regulated within broad limits by adjusting the deposition time. The electrokinetic properties of hematite monolayers produced in this way were studied using the streaming potential method. The dependencies of the monolayer zeta potential on the coverage, pH and ionic strength were determined. Hematite monolayers were used as heterogeneous substrates for colloid particle deposition studies involving negatively charged polystyrene latex particles (800nm in diameter). An anomalous deposition of latex particles on substrates exhibiting a mean negative zeta potential was observed for higher ionic strength. These deviations from the classical DLVO theory were quantitatively interpreted in terms of the heterogeneous nanoparticle coverage distribution governed by fluctuation theory. However, for low ionic strength of 10−4M latex particle deposition proceeded in accordance with the DLVO theory. These data obtained for hematite can be used as useful reference states for analyzing particle or bacteria adhesion to heterogeneous surfaces covered by macromolecules and proteins.