8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Fri 911:10-14:00P4.51Piston-rotaxanes as molecular shock-absorbersEdie Sevick 1 and David Williams 21 The Australian National University, Research School of Chemistry, 0200, Canberra,Australia2 The Australian National University, Canberra, AustraliaA rotaxane is a molecule that is architecturally similar to some baby rattles: one or more ring-likemolecules threaded onto a molecular axle that is capped on both ends with stoppers to prevent therings from falling off. These materials were first synthesised only 40 years ago. One of the mostinteresting features of these rotaxanes is the ability of a ring to slide along the axle. For example,by tuning strong enthalpic interactions within the molecule, chemists can entice a ring to coverspecific portions of the axle - this can be used to shield particular chemical groups so as to impart achangeable molecular hydrophobicity or reactivity. However these rings don’t need to be enthalpicallylocalised: these rings can shuffle along the axle and their translational entropy leads to anarray of interesting soft properties. In this talk we describe soft properties of entropy-dominatedrotaxane molecules, specifically a piston-rotaxane (P-R) which behaves as a scaled-down versionof automobile shock-absorber. These include predictions of (i) the equilibrium thermo-mechanicalresponse of a single piston-rotaxane [1], and (ii) the micro-valve behaviour of a surface graftedwith these molecules [2], as well as predictions of (iii) the molecule’s non-equilibrium responsethat is comparable with single molecule force spectroscopy [3] and which characterises the shockabsorbingproperties. [1] EM Sevick & DRM Williams. “Piston-Rotaxanes as MolecularShock Absorbers. ” Langmuir 26, 5864-5868, (2010). [2] RJ Boesten, EM Sevick, & DRMWilliams. “Piston Rotaxane Mono layers: Shear Swelling and Nanovalve Behavior. ” Macromoelcules,43, 7244-7249 (2010) [3] YX Gao, DRM Williams, & EM Sevick, “Dynamics ofmolecular shock-absorbers: energy dissipation and the Fluctuation Theorem”, submitted to SoftMatter Jan 2011.51