Experimental study of migration of shape-specific particles and its applications in fluidic self -assembly

Fluidic self assembly (FSA) is a promising new method for manufacturing microscopic assemblies, which offers impressive advantages over traditional “top-down” fabrication methods. It works automatically by transporting large numbers of micro devices using hydrodynamic steering. The interaction of the fluid flow, the shape of the part, and the orientation and the shape of the binding sites all contribute to the final yield of the assembly process. Therefore, investigating the role of fluid forces during assembly is essential for optimizing of the FSA process. In this thesis, a novel photolithography-based direct particle fabrication technique is presented that can be used to fabricate polymeric micro particles of varied and complex shapes with high throughput. This technique offers fine control over particle size and shape. These shape-specific particles can be used to model the micro devices used in FSA process. To study the orientation and translation of such particles sliding on the substrate in a flow field can be very useful to improve the efficiency of the assembly process. Previous analytical and experimental works on single particle motions in viscous fluid are reviewed. Although there are no directly comparable analytical results, analytical trends and dependences on parameters in simplified system can shed some light on FSA performance. In particular, elliptical particles in simple shear flow show a potential of aligning particles by hydrodynamic forces. A flow system is set up and experiments are carried out using particles of assorted shapes. Experimental results show the tendency of those particles to align to preferred orientations in the flow chamber by hydrodynamic forces. A micro imaging system is used to image the position and orientation of the particles. The preferred orientation of particles with different shapes was measured using algebraic moment theory. Rectangular particles were assembled onto a substrate with complementary recesses of varying angles relative to the flow direction. It is observed that a simple change in the orientation of the recesses can drastically change the final assembly yield from more than 90% to less than 50%