Extreme mechanics of colloidal polymers under compression: Buckling, creep, and break-up

Self-assembling patchy colloidal particles form a promising platform to create designer soft materials. To dress such systems with mechanical functionality, one can take inspiration from biological structures such as the cell's cytoskeleton, which consists of semiflexible filaments, whose mechanical behavior give the cell its unique mechanical properties. Here we present mechanical experiments on analogs of biological fibers, semiflexible "colloidal polymers"made from bonded patchy colloidal particles. We use optical tweezers to probe their extreme mechanics under increasingly high compressions and we reveal a rich nonlinear mechanical response involving buckling, viscoelastic creep, and ultimately break-up. We characterize and model this response using elastic and viscoelastic models involving Euler buckling and stress relaxation. This allows us to identify the critical Euler buckling force, and relate the critical bending at break-up to the finite patch size of the colloids. These results demonstrate the crucial role of the patch-patch interactions in the mechanics of self-assembled colloidal materials, and they provide mechanical relationships that are essential to design functional colloidal architectures inspired by nature.