A novel colloid probe preparation method based on chemical etching technique

Several fundamental problems in hydrophobic force measurements using atomic force microscope (AFM) are dis-cussed in this paper. A novel method for colloid probe preparation based on chemical etching technology is proposed, which is specially fit for the unique demands of hydrophobic force measurements by AFM. The features of three different approaches for determining spring constants of rectangular cantilevers, including geometric dimension, Cleveland and Sader methods are com-pared. The influences of the sizes of the colloids on the measurements of the hydrophobic force curves are investigated. Our experimental results showed that by selecting colloid probe with proper spring constant and tip size, the hydrophobic force and the complete hydrophobic interaction force curve can be measured by using AFM.

Interfacial forces between silica surfaces measured by atomic force microscopy

Colloidal particle stability and some other interfacial phenomena are governed by interfacial force interactions. The two well known forces are van der Waals force and electrostatic force, as documented by the classical Derjaguin, Landau, Verwey, and Overbeek （DLVO） theory. Moreover, advances in modern instrumentation and colloid science suggested that some short-ranged forces or structure forces are important for relevant colloidal systems. The interfacial and/or molecular forces can be measured as a resultant force as function of separation distance by atomic force microscopy （AFM） colloid probe. This article presents a discussion on AFM colloid probe measurement of silica particle and silica wafer surfaces in solutions with some technical notifications in measurement and data convolution mechanisms. The measured forces are then analyzed and discussed based on the ＇constant charge＇ and ＇constant potential＇ models of DLVO theory. The difference between the prediction of DLVO theory and the measured results indicates that there is a strong short-range structure force between the two hydrophilic surfaces, even at extremely low ionic concentration, such as Milli-Q water purity solution.

Effect of surface roughness on sliding friction of micron-sized glass beads

In order to understand the contact phenomena of micron‐sized particles,which have a tremendous impact on a variety of applications in industry and technology,direct access to the loads as well as the displacements accompanying such contacts are mandatory.Typical particle ensembles show a size variation ranging from the nanometer to the tenths of micron scale.Especially the contact behavior of particles featuring radii of several up to several tenths of microns is scarcely studied as these particles are typically too large for atomic force microscopy(AFM)based approaches and too small for conventional macroscopic testing setups.In this work a nanoindenter based approach is introduced to gain insight into the contact mechanics of micron‐sized glass beads sliding on rough silicon surfaces at various constant low normal loads.The results are analyzed by a simple modified Coulomb friction law,as well as Hertz,JKR,and DMT contact theory.