Effect of Surface Geometric Structure on the Adhesion Force between Silica Particles

Abstract

The adhesion force between nonporous and porous silica particles was measured by AFM as a function of relative humidity. Various porous samples were prepared by hydrothermal treatments in different conditions. Geometric structure was evaluated by gas adsorption, and the mechanism of rehydroxylation that occurred in hydrothermal treatments was investigated by silanol density, IR spectra, and immersional heat. The adhesion force was measured by AFM, and the result was compared with the geometric structure and the rehydroxylation process. As a result, we proved that capillary condensation occurred in small spaces between two particles contacting each other after water filled the pores and capillary force appeared to contribute to a steep increase of adhesion force. The adhesion force under low relative pressure was attributed to hydrogen bonding force and reflected both the contact area and hydrophilicity of the surface.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Adhesion forces increased with humidity on the arrays but did not on single asperities, indicating that humidity increased the number of asperities contacted by the flat tip. Fuji et al [691] found a reduced dependence of adhesion on relative humidity for porous silica particles compared to solid ones. This was attributed to the larger roughness/pore size of the porous particles that hindered the formation of capillary bridges.…”

On the Adhesion between Fine Particles and Nanocontacts: An Atomic Force Microscope Study

“…Many experiments showed a significant dependency of the adhesion force on the relative humidity [40,52,54,56,57,183]. A continuous increase humidity was, for example, observed for the interaction of a silicon nitride tip with mica [194], between silica particles [199], a silica particle and a silicon wafer [200], or between a silicon nitride tip and molybdenum trioxide [201]. The adhesion force between particles or particle surface by using AFM colloidal probe technique depending on relative humidity [190,202,203].…”

“…Some results of our experiment showed that the magnitude of the adhesion forces changes on mica and quartz surfaces and observed that maximum of adhesion forces at relative humilities around 20% or less 45%. Results of other studies showed that meniscus force between silica particles [62,63], a silica particle and a silicon wafer [64], between a silicon nitride tip and molybdenum trioxide [65], or pharmaceutical substances [66], and between silicon wafer and silicon nitride tip was at relative humidity around 70% [67]. In other cases adhesion force-versus-humidity curves showed a maximum [42,58,68], or a step-like increase [69].…”

The Colloidal Probe Technique and its Application to Adhesion Force Measurements

“…Reducing the pressure from 760 Torr to 0.6 Torr which should reduce the adsorbed water layer from $ 2 nm to a single monolayer, diminished the adhesion force by only 10%. Fuji et al [72] studied the influence of relative humitidy and surface structure on adhesion between single silica particles in a nitrogen atmosphere. Smooth, nonporous silica particles and particles with different pore sizes were used.…”