Abstract
Shear-induced particle order in concentrated colloidal dispersions is well-known and has been studied a great deal. Although applications of this phenomenon do rely on the post-shear particle order, there has been little understanding about the post-shear structures. Here, aiming at better post-shear order, namely higher crystallinity, we study the effects of experimental conditions, i.e., particle concentration, viscosity and pH of the suspensions of styrene-butadiene copolymer latex on the post-shear structures. Viscosity was varied by the addition of polyethyleneglycol and pH was varied by the addition of either HCl or NaOH aqueous solution. Reflection measurement was employed to evaluate the structures and carried out in-situ in a rotational rheometer with transparent cone-and-plate type shear-cell under shear flow and in post-shear. The structures were quantified by wavelength and intensity of the reflection peak normalized by initial spectrum before shear flow. We found that the crystallinity that had vanished after turning off the shear flow resurged spontaneously to yield structures with much higher crystallinity in appropriate conditions. It was revealed that the resurgence of the crystalliniy was promoted both by higher particle concentration and more basic condition (greater inter-particle repulsion), which agrees with previous studies on 2D colloidal crystals in terms of providing higher crystallinity.
