Directed Self Assembly (DSA) methods are used to assemble particle suspensions into useful structures and devices using particles ranging in size from nanoparticles to non-Brownian particles. In this work, oscillatory shear fields are being explored as methods for DSA. The focus of the work is developing a basic understanding of how these methods can be harnessed to generate three-dimensional ordered structures. Potential applications of these highly ordered structures are for photonic devices or for materials with consistent mechanical properties dictated by repeating structure. DSA methods create highly ordered three-dimensional structures under predictable experimental conditions.

Prior work has demonstrated that colloidal dispersions can be ordered by oscillatory shear fields within specific amplitudes and frequencies. However, creating ordered structures with non-Brownian particles in the ~10-100 ìm range is challenging. This work shows that Large Amplitude Oscillatory Shear (LAOS) imparts particle mobility through shear-induced diffusion that can direct ordering. This is demonstrated on monodisperse particle suspensions between 1 and 65 microns. This study explores the degree of order by varying particle loading and other rheometric parameters such as shear amplitude and frequency. A custom built Rheo-SALS device is used to monitor the degree of order (through light scattering) and rheokinetics of the ordering process. The Rheo-SALS device allows for direct observations of the disordered particle state into the ordered regions of a six spot Bragg pattern. The order parameter is determined from the light scattering results and compared with the degree of order monitored via the kinetic data. Further, use of epoxy and polymer glass forming matrices enables direct examination of the ordered structure through scanning electron microscopy. The degree of ordering compares well with colloidal particles of much smaller sizes. LAOS ordering is reproducible and is potentially scalable for industrial manufacturing.