Directed self-assembly of suspensions by large amplitude oscillatory shear flow.

Prior work has demonstrated that colloidal suspensions can be ordered with large amplitude oscillatory shear (LAOS), showing that the final type and degree of ordering depends on the frequency and amplitude of the applied oscillation. Here, we present LAOS results for the kinetics of ordering for colloidal particles (d=1 μm) at [lowercase_phi_synonym]=0.54 from a shear disordered state over a range of frequencies and shear amplitudes. A custom rheolight scattering (rheo-LS) device is used to quantify the type and degree of crystalline order observed either as a six spot Bragg pattern or a three streak twinning pattern. The dynamic shear stress and the alignment factor derived from the rheo-LS show the same time-dependent behavior indicative of a primary relaxation that is exponential in time. The rate of ordering to the r-hcp state is found to scale with the amplitude of oscillation and inversely with the frequency over strains from 100% to 300% and frequencies from 0.5 to 5 Hz. These results show that the rate of LAOS ordering does not simply reflect the rate of deformation, but rather a more complex mechanism pointing toward competition between shear ordering and shear-induced defect generation. [ABSTRACT FROM AUTHOR]