Direct Detection of the Solvent Molecules between Solid Surfaces with Simultaneous Adhesion Force Measurement

Abstract

In this study, we applied the force curve mode confocal laser scanning/atomic force microscope (CLSM/AFM) to detect solvent properties in the contact area with the simultaneous force measurement. Two experimental approaches were carried out. First, we performed an adhesion force measurement between a carboxylated polystyrene microbead and the substrate surface that has the terminus group of −NH2 or −CF3 at various pH by the traditional AFM measurement. The results revealed that the hydrophobic interaction and hydrogen bonding force operates when the microbead is brought into contact with the −CF3 and −NH2 surface, respectively. Next, the solvent molecules between solid surfaces were detected with the simultaneous adhesion force measurement by the CLSM/AFM system. The results revealed that the fluorescence intensity of fluorescein was decreased only when the hydrophobic interaction worked. It was due to the removal of solvent molecules in the contact area, and the hydrophobic surfaces stabilize each other by making the contact area hydrophobic. On the other hand, when the hydrophilic interaction, such as hydrogen bonding, operates, the solvent molecules exist in the contact area.