ABSTRACT
To optimize handling of fine powders or cleaning of surfaces in industrial applications an understanding of the interaction forces between single particles and between particles and different substrate materials is fundamental. A classical method for measuring the adhesion of small particles to surfaces is the centrifuge technique [ 1-7], where the centrifugal force required to detach a particle from a surface is determined. Usually the detachment force for many particles is recorded in a single experiment, yielding statistics on the distribution of adhesion forces, e.g., for irregularly shaped particles. With the invention of the atomic force microscope (AFM) in 1986 [8] and the introduction of the so-called "colloid probe" technique [9, I 0] (Fig. I), a direct measurement of interaction between single
We have built an apparatus (see Fig. 2) that is based on the principle ofthe AFM but has been optimized for the measurement of inter-particle forces [11]. Therefore, we call it Particle Interaction Apparatus (PIA). The main design differences between PIA and most commercial AFMs are:
The piezotranslators have a relatively large maximum extension of 12 J.!ffi and are equipped with capacitive sensors to allow for closed loop operation. This avoids creep and drift problems by the piezotranslators. The detector is not a split photodiode but a position sensitive device (PSD) with an active area of 20x20 mrn. This results in a larger dynamic range of the detector. The mechanical design leaves ample room for sample access and gives the option for a side view of the interacting particles with a video microscope. The system is controlled by self-written software that can readily be adapted to specific experimental needs (e.g., non-linear movement of the piezotranslators ).
