Effects of Translation-Rotation Coupling on the Displacement Probability Distribution Functions of Boomerang Colloidal Particles

摘要

Prior studies have shown that low symmetry particles such as micro-boomerangsexhibit behaviour of Brownian motion rather different from that of highsymmetry particles because convenient tracking points (TPs) are usuallyinconsistent with the center of hydrodynamic stress (CoH) where thetranslational and rotational motions are decoupled. In this paper we study theeffects of the translation-rotation coupling on the displacement probabilitydistribution functions (PDFs) of the boomerang colloid particles with symmetricarms. By tracking the motions of different points on the particle symmetryaxis, we show that as the distance between the TP and the CoH is increased, theeffects of translation-rotation coupling becomes pronounced, making theshort-time 2D PDF for fixed initial orientation to change from elliptical tocrescent shape and the angle averaged PDFs from ellipsoidal-particle-like PDFto a shape with a Gaussian top and long displacement tails. We also observedthat at long times the PDFs revert to Gaussian. This crescent shape of 2D PDFprovides a clear physical picture of the non-zero mean displacements observedin boomerangs particles.