Surface Forces between Nanomagnetite and Silica in Aqueous Ca2+ Solutions Studied with AFM Colloidal Probe Method

Abstract

Dispersion and aggregation of nanomagnetite (Fe3O4) and silica (SiO2) particles are of high importance in various applications, such as biomedicine, nanoelectronics, drug delivery, flotation, and pelletization of iron ore. In directly probing nanomagnetite–silica interaction, atomic force microscopy (AFM) using the colloidal probe technique has proven to be a suitable tool. In this work, the interaction between nanomagnetite and silica particles was measured with AFM in aqueous Ca2+ solution at different pH levels. This study showed that the qualitative changes of the interaction forces with pH and Ca2+ concentrations were consistent with the results from zeta-potential measurements. The repulsion between nanomagnetite and silica was observed at alkaline pH and 1 mM Ca2+ concentration, but no repulsive forces were observed at 3 mM Ca2+ concentration. The interaction forces on approach were due to van der Waals and electrical double-layer forces. The good fitting of experimental data to the DLVO model and simulations supported this conclusion. However, contributions from non-DLVO forces should also be considered. It was shown that an increase of Ca2+ concentration from 1 to 3.3 mM led to a less pronounced decrease of adhesion force with increasing pH. A comparison of measured and calculated adhesion forces with a few contact mechanics models demonstrated an important impact of nanomagnetite layer nanoroughness.

Enhancing Water Resistance in Cationic Cellulose Nanofibril Adhesive with Natural Rubber Latex

“…The approach and retraction curves for the uncoated tip demonstrated a clear repulsion, starting at an interaction distance of about 105 nm, and no adhesion peak occurred during tip release. This repulsive behavior, already observed in similar systems, − can be expected due to the double-layer repulsion between negatively charged groups on both SiO 2 and mica surfaces . On the other hand, after coating the SiO 2 probe with CCNFs, no repulsive force was detected in the approach path.…”

Toward an Improved Method for Determining the Hamaker Constant of Solid Materials Using Atomic Force Microscopy. II. Dynamic Analysis and Preliminary Validation

“…Hence, the proposed method is applicable only for the estimation of Hamaker constants in similar dry environments. Yet, there are several systems of interest in which vdW interactions occur across an intervening liquid medium and for which accurate knowledge of these corresponding Hamaker constants is important (e.g., aggregation of colloidal particles in aqueous dispersions − ). The extension of our method to such systems would be worthwhile where the cantilever tip moving toward the substrate would now also experience hydrodynamic forces from the intervening medium.…”

Charge-Regulated Interactions: The Case of a Nanoparticle and a Sphere of Arbitrary Dielectric Constants

“…In this context, we consider here the problem of the electrostatic interaction of a sphere and a charged particle in an aqueous electrolyte. Technologically, the study of microspheres interacting with nanoparticles has been used to understand stabilization of binary colloids , and the related intersphere/-particle interactions , and sphere–particle interactions, for high energy density storage in electronic devices, and for drug delivery design. , For example, this system serves as a model for a silica microsphere interacting with viruses, − as well as to understand the forces between atomic probe microscopy sensors and charged nanoobjects − (Figure ).…”