Dynamics of a colloid-in-tube host-guest system.

Originated from supramolecular chemistry, the host-guest concept is generalized and appreciated across the fields of enzyme catalysis, biological channel conduction, and carbon nanotube transport, to name a few. Despite the extensive study of host-guest thermodynamics, it is still a fundamental challenge to directly measure its dynamics in real-space and real-time. Herein we approach such dynamics by direct imaging and tracking in a colloid-in-tube system, where self-assembled tubes are the hosts and sphere particles are the guests. The key difference from a previously reported static 1D confinement is that the present tubes are thermally actuated and capable of translations and rotations. It is the host tube thermal motions that impose a number of anomalies to guest particle dynamics including broadened distribution perpendicular to the tube, enhanced diffusion parallel to the tube phenomenologically resembling the rapid flow in ion channels or carbon nanotubes, and induced long-range particle-particle attraction analogous to capillary condensation. This work in the colloidal system is of wide implications for host-guest systems that are naturally embedded in thermal fluctuations such as transmembrane ion channels and carbon nanotube arrays in a soft matrix.