Piston-rotaxane as a molecular shock absorber

Rotaxanes are molecules architecturally similar to some baby rattles: one or more ring-like molecules threaded onto a molecular axle which is capped on both ends with large stoppers to prevent the rings from sliding off. These molecules were first synthesized over 40 years ago and their structural motif has been recognized in some proteins. The rings of these rotaxanes can be exploited to impart novel thermo-mechanical properties to these molecules. We couple an external piston to one of the rings of a rotaxane molecule, Fig A, and exploit the gas-like entropy of the other rings to determine the piston's elastic response. We refer to this molecular design, where the piston can compress the axle-bound rings, as a piston-rotaxane. In 2010, we introduced rotaxanes as entropy-dominated molecules, resulting in (i) predictions of  equilibrium properties  from exact partition functions, (ii) predictions of  micro-valve response of piston-rotaxane brushes that line interior of conduits, and (iii) determined optimal molecular design parameters based upon non-equilibrium dynamics. (With  Y.X. Gao, D.R.M. Williams (RSPE), R.J. Boesten (RSPE)].


  • E.M. Sevick and D.R.M. Williams, “Piston-Rotaxanes as Molecular Shock Absorbers”,  Langmuir, 26, 5864-5868 (2010).
  • R. Boesten, E.M. Sevick, D.R.M. Williams, “Piston-rotaxane monolayers: shear swelling and nanovalve behaviour”, Macromolecules 43, 7244-7249 (2010).
  • E.M. Sevick, "Compression-Induced Phase Transitions in Water-Soluble Polymer Brushes:  The n-Cluster Model", Macromolecules 31, 3361-3367, 1998
  • E.M. Sevick and D.R.M. Williams, "Polymer brushes as Pressure-Sensitive Automated Microvalves", Macromolecules 27, 5285-5290, 1994.