A combination of TSM and AFM for investigating an interfacial interaction of particles with surfaces

Interactions of microparticles and nanoparticles with various surfaces under different ambient conditions are of great importance to many applications such as micro-electrical-mechanical systems (MEMS), biomedical and chemical engineering, and have attracted broad interests in the last decade. However, there are only limited numbers of techniques currently available for interfacial particle analysis. In this paper, we propose to use a piezoelectric quartz sensor in a thickness shear mode (TSM) to characterize the interfacial interaction of a single microparticle with a surface. A theoretical model was developed based on the analysis of the various interaction forces, including Van der Waals (VDW) force, capillary force and electrostatic force, etc. The dependence of the particle-surface interaction forces on the particle size was demonstrated. Experimental results from a 5MHz TSM sensor have shown an average frequency shift of 0.5 Hz for a 40 mum stainless steel sphere, which indicated that a coupling strength between a sphere and a surface is about 1.3times10⁴ N/m. An atomic force microscope (AFM) was used to provide a complementary tool to help study the interfacial interactions. Adhesion forces between particles and surfaces were measured and favorably compared with the simulation results. It is shown that a TSM sensor is capable of real-time analyzing an interaction of a single microparticle with a surface and an AFM is helpful to identify the effect of each individual interaction force. A combined TSM-AFM technique may create a novel measurement platform for characterization of nanoparticles and their interactions with surfaces