Impact-shear-induced millisecond clustering during shear melting of colloidal crystals.

A uniform, dense suspension of silica particles forms a colloidal crystal, which undergoes shear-induced melting upon the application of flow. Shear melting induced by impact-shear typically initiates within milliseconds and completes within a few seconds, making the transition difficult to observe. Here, we developed a rheometric technique integrating fast time-resolved small-angle X-ray scattering (SAXS) with millisecond time resolution, which revealed the evolution of Bragg peaks characteristic of crystalline order, allowing direct observation of the melting transition. We report that anisotropic disordering induced by the impact shear indicates momentary particle clustering and is attributed to rapid interlayer sliding within the close-packed colloidal structure. These findings uncover a fast shear melting mechanism inaccessible to conventional rheological techniques and highlight the utility of the high-speed structural characterization. The developed rheometric technique, integrating fast time-resolved SAXS, brings valuable insights into shear-responsive colloidal systems and holds potential for applications in colloid-based technologies.