Kayaking and wagging of liquid crystals under shear: Comparing director and mesogen motionsY.-G. Tao0, W. K. den Otter1 and W. J. Briels1
1 Computational Biophysics, Faculty of Science and Technology, University of Twente P.O. Box 217, 7500 AE Enschede, The Netherlands, EU
received 27 March 2009; accepted in final form 26 May 2009; published June 2009
published online 23 June 2009
Rod-like colloids in dense solutions perform collective orientational motions under shear flow. The periodic tumbling motions of the director, i.e. the average orientation of the rods, are commonly characterized as kayaking, wagging and flow-aligning, in order of increasing shear rate. Our event-driven Brownian dynamics simulations of rigid spherocylinders reproduce these three distinct director motions, but also clearly show, for the first time, that the individual mesogens are kayaking at all shear rates. The synchrony of the mesogens's motions gradually decreases with increasing shear rate, which at a critical shear rate causes a transition of the apparent collective motion from kayaking to wagging. The rods's persistent kayaking also explains the continuity of the tumbling period at this transition and the smooth change from wagging to flow-aligning observed at higher shear rates.
61.30.Cz - Molecular and microscopic models and theories of liquid crystal structure.
82.20.Wt - Computational modeling; simulation.
83.10.Mj - Molecular dynamics, Brownian dynamics.
© EPLA 2009