Abstract:
Interaction between particles and different surfaces under ambient condition is studied using AFM-based force spectroscopy. This work focuses on the adhesion mechanism and factors affecting particle-surface adhesion. The particles of interest consist of magnesium silicate (talcum powder) and zinc oxide (ZnO) particles, which have very attractive properties and are widely used in several applications. The adhesion force measurements were first carried out using silicon/silicon coated with DLC probes pressed on talc particles modified with hydrochloric acid or different organosilanes. These modifications change hydrophobicity and hydrophilicity of the particles. The results show that the adhesion forces are distributed in a bimodal fashion. It is postulated that they originate from two types of surface of talc particles, i.e., face surface (hydrophobic character) and edge surface (hydrophilic character). The adsorption and adhesion strength are in the following trend: hydrophilic-hydrophilic > hydrophilic-hydrophobic > hydrophobic-hydrophobic. Similar bimodal distribution was also observed for ZnO particles, of which could be distinguished by controlling the shape of particles. The polar surface is obtained from the top and bottom of micron-sized ZnO powder while the nonpolar surface is obtained from the side plane of ZnO nanorods. Moreover, interaction with AFM probes that were chemically modified with different terminal functional groups was also investigated, in order to describe relationship between the adhesion interactions and adsorption mechanism. The results show the same trend as in talc particles, i.e., polar-polar interaction is stronger than polar-nonpolar interaction, and the weakest adhesion was observed from nonpolar-nonpolar interaction. However, electronic distribution and the atomic arrangement on the surface also affect the adhesion. In general, this work demonstrates that the intermolecular forces are important for the particles-surface interactions, especially van der Waals forces and hydrophobic effect.
