Orientation-Specific Dynamic Shape Factors for Doublets and Triplets of Spheres in the Transition Regime

ABSTRACT

The dynamic shape factor for singly charged doublets and triangular triplets of uniform spheres (polystyrene latex particles) in the Knudsen number range 0.2–1.3 has been measured using a differential mobility analyzer (DMA). The shape factor turned out to be dependent on the intensity of the electric field created in the DMA. Thus, for doublets it was found that at low field strengths the point charge on the particles causes them to be inclined 45° with respect to the electric field, whereas at higher field intensity they become parallel to the field due to induced polarization. The adjusted diameter of the sphere having the same slip-correction factor as the nonspherical particle has also been discussed. The adjusted diameter was found to be almost the same as the volume equivalent diameter in the case of 45°-oriented particles.