Brownian motion of freely jointed colloidal trimers.

Shape changes resulting from segmental flexibility are ubiquitous in molecular and biological systems, and are expected to affect both the diffusive motion and (biological) function of dispersed objects. The recent development of colloidal structures with freely-jointed bonds and flexible chains have now made a direct experimental investigation of diffusive shape-changing objects possible. Here, we show the effect of segmental flexibility on the simplest possible model system: a freely-jointed cluster of three spherical particles. By combining experiments and modelling, we find a 3 percent enhancement of diffusivity compared to rigid clusters. Unique to flexible assemblies, we find that in addition to the rotational diffusion time, an analogous conformational diffusion time governs the relaxation of the diffusive motion. Additionally, we find a Brownian quasi-scallop mode, where diffusive motion is coupled to Brownian shape changes. Our findings could have implications for transport properties in molecular and biological systems, such as functional site availability in lock-and-key protein interactions.