The Physics of Colloidal Chains

Spherical colloidal particles have emerged as model systems for gaining insights into different phenomena in condensed matter and statistical mechanics, such as crystallization and the glass transition. Here we make “polymeric” colloidal chains by stringing colloidal beads together using an elegant method called ice templating. Colloidal polystyrene latex particles are coated with polymer (polyethylenimine) and are crosslinked using diepoxy compounds to form colloidal chains. We can vary the chain flexibility simply by varying crosslinking time. We use optical microscopy to observe the colloidal chains and obtain the spring constant between colloidal monomers and the chain bending rigidity. We investigate semi-flexible colloidal chains and show that their center of mass diffusion scales with N^-0.6, where N is the number of beads in the chain. Surface modification of the colloidal beads lends functionality to the chains. Coating the beads with catalyst allows us to achieve out-of-equilibrium active systems that show enhanced center of mass diffusion. Grafting thermoresponsive polymers to the colloidal surface allow us to create colloidal chain assemblies that are sensitive to temperature variations.