Friction Properties of Polymer Systems as Measured Using Micropipettes

Abstract

<p>In this work, we tested the ability of an experimental system, involving the use of micropipettes as force transducers, to measure the coefficients of friction of several systems. Using a magnetic pipette puller, the micropipettes were produced by first heating and stretching the glass. The pipettes are then manipulated into an L-shape. This geometry allows one arm to act as the normal force transducer, and the other to act as the lateral force transducer for the purposes of friction measurements. We then analyzed the variation of the friction force of 15 micrometre polystyrene beads in contact with silicon and polystyrene in a fluid environment at increasing velocities. We also measured the variation in friction coefficient of poly(dimethyl siloxane) coated polystyrene beads in contact with a silicon surface. Our results were then compared to known values where possible, and the variation of the friction coefficient with increasing velocity was fit to a known phenomenological model. From our experiments, we have shown that our experimental technique can provide reproducible friction coefficient measurements, and these coefficients vary with velocity in a known manner. These results confirm the ability of micropipettes to act as both normal and lateral force transducers in friction experiments, and that they have the potential to be used in measuring friction coefficients of more complex materials.</p>