Effect of scission on alignment of nonionic surfactant micelles under shear flow.

We investigate the alignment of wormlike micelles under shear flow with dissipative particle dynamics simulations of nonionic surfactant solutions. To reveal the effect of micellar scission on alignment, we evaluate the shear-rate dependence of the mean orientation angle and the average lifetime of micelles for fixed aggregation numbers. Our numerical results demonstrate the presence of two distinct shear-rate regimes of micellar alignment. In the low shear-rate regime, where flow-induced scission does not occur, wormlike micelles align more in the flow direction with the shear rate. In contrast, flow-induced scission suppresses micellar alignment in the high shear-rate regime. In addition, comparing the alignment of wormlike micelles with that of polymers without scission, we find that the mean orientation angle of wormlike micelles is larger than that of polymers when flow-induced scission occurs. This comparison confirms that flow-induced scission yields the unique behavior of micellar alignment. Furthermore, we demonstrate that flow-induced scission suppresses micellar alignment for fixed aggregation numbers by reducing the effective longest relaxation time of micelles.