  Ring, or cyclic, polymers have unique properties compared to linear polymers,
due to their topologically closed structure that has no beginning or end.
Experimental measurements on molecular ring polymers are challenging due to
their polydispersity in molecular weight and the presence of undesired side
products such as chains. Here, we study an experimental model system for cyclic
polymers, that consists of rings of flexibly-linked micron-sized colloids with
$n$=4..8 segments. We characterize the conformations of these flexible
colloidal rings and find that they are freely-jointed up to steric
restrictions. We measure their diffusive behavior and compare it to
hydrodynamic simulations. Interestingly, flexible colloidal rings have a larger
translational and rotational diffusion coefficient compared to colloidal
chains. In contrast to chains, their internal deformation mode shows slower
fluctuations for $n\lesssim 8$ and saturates for higher values of $n$. We show
that constraints stemming from the ring structure cause this decrease in
flexibility for small $n$ and infer the expected scaling of the flexibility as
function of ring size. Our findings could have implications for the behavior of
both synthetic and biological ring polymers, as well as for the dynamic modes
of floppy colloidal materials.
