Rheology of Self-Assembling Colloidal Chains

We probe the rheology of self-assembling chains of ``pacman'' particles using a Zimm viscometer, a modified Couette apparatus. Pacman particles are microscopic spherical particles specially designed to have a spherical indentation on their surface. In the presence of a depletant, overlap between the indentation and another particle's surface maximizes the excluded volume between the two interacting particles, resulting in a selective attraction between them. Careful tuning of the interaction strength in a suspension of particles induces the formation of long chains. Shearing this material can twist, stretch, and break the chains, causing the material to exhibit unique rheological properties.