Influence of Particle Interactions and Effective Gravity on the Structure of Colloidal Rod Sediments

Colloidal rod sedimentation is a multifaceted phenomenon influenced by various factors, encompassing sedimentation rate, viscosity, particle size distribution, inter-particle interactions, and hydrodynamics. These elements contribute to fluctuations and instabilities during sedimentation, impacting particle packing fractions crucial for material jamming. In this study, colloidal rods were synthesized through high shear rates employing SU-8, a photoresist, resulting in aspect ratios ranging from 2 to 4 following careful cleaning and fractionation. The investigation centers on colloidal rods suspended in diverse surfactant concentrations. Notably, higher surfactant concentrations yield pronounced nematic ordering, while reduced surfactant concentrations or water lead to diminished order. We describe the conditions necessary to generate reproducible sedimentation structures, and find that the interaction between surfactants and the rods in the sediment controls the order within the sediment.