Effect of magnetic field on molecular orientation of nematic liquid crystalline polymers under simple shear flow

摘要

The effect of magnetic fields on molecular configuration of liquid crystalline polymers (LCPs) under shear flows is numerically analyzed using the Doi theory. The evolution equation for the probability density function of the liquid crystalline polymer (LCP) molecules is directly solved without any closure approximations. Two cases of the magnetic fields are considered: (1) the magnetic field parallel to the flow direction, and (2) the magnetic field parallel to the velocity gradient direction. For both cases, the magnetic fields strongly affect the transition among flow-orientation modes, such as tumbling, wagging, and aligning modes. When the magnetic field is imposed on the LCP shear flow, a new aligning flow-orientation mode emerges at low shear rate, which is macroscopically the same, but microscopically quite different from the ordinary aligning mode. For the magnetic field parallel to the flow direction, the field affects the scalar order parameter rather than the major orientation direction. On the other hand, for the magnetic field parallel to the velocity gradient direction, the effect of the field on the major orientation direction is more remarkable than the effect on the scalar order parameter. (C) 2008 The Society of Rheology.