Statistical Mechanics of Rotaxane Switches

Abstract

A solution of rotaxane switches, which can switch their length by external stimuli, is described using statistical thermodynamics. We show that this solution can exhibit different behaviors. This solution can rapidly switch between isotropic and nematic liquid crystalline phases without altering temperature and concentration. There is a minimum of 13% length extension for which transition from pure isotropic to pure nematic phase is possible in idealistic system. We provided a framework to help synthetic chemists understand the requirements of switching efficiency, length change and concentration in rotaxane chemical design to create a macroscopic liquid crystalline phase change. When external rotaxane switches are depletants in the solution, length switching of rotaxane can significantly change the range and magnitude of colloid depletion interaction. This indicates a possible application of rotaxane switch in controlling colloid stability. We also investigate liquid crystalline behavior in solution of a rotaxane switches which change length to "adapt" to surrounding environment. We find the effect of adaptive length change on liquid crystalline behaviors is most dramatic at relatively low length extension.