(256e) Colloidal Surface-Anisotropy Toolbox for Engineering Suspension Flow

Colloidal suspensions are ubiquitous in everyday life, with applications ranging from household products to construction materials. Predicting their flow properties is a challenging engineering problem due to the diverse nature of solvent-particle interactions and particle properties, such as surface roughness, size polydispersity, and deformability. Prior experiments and simulations conducted in academic settings focus on ideal (spherical and frictionless) colloids. Here, we decouple the effects of particle surface anisotropy by probing the flow behavior of dense suspensions rough poly(methacrylate) colloids. In dense suspensions, the rough colloidal particles showed restricted rotational motion due to additional frustration introduced by the surface asperities. We study the rheological behavior associated with the restricted dynamics in these dense suspensions by probing them using an array of rheological protocols: from small amplitude oscillations to high steady shears. In addition, we assembled a confocal rheometer, which for the first time allowed the 3D visualization of suspension microscopic structure in-situ, while being sheared. Our results showed that the flow properties between smooth and rough colloidal suspensions can be clearly explained through the free space available for the particles to rearrange under flow. We found that the two material properties, suspension elasticity at low shear and shear thickening rate at high shear, depend on one single parameter - the jamming distance. Jamming distance is defined by how far a given dense suspension concentration is from its maximum possible concentration. Since smooth and rough particle suspensions have roughness-dependent maximum jamming concentrations, jamming distance is a fixed parameter for a given colloidal suspension. Thus, tuning the surface roughness enabled us to design a material toolkit that maps to the respective rheological properties. This framework, based on the jamming properties of the suspension material, is fundamental in engineering elastic properties and thickening behavior in dense colloidal suspensions.