Swelling of Tendomer Gels

Abstract

We propose a new type of polymer gels made of tendomers as elastic elements. Tendomers are a pair of rotaxanes with a specific nonlinear response and an almost step-like softening transition by increasing their extension. We consider the swelling equilibrium of tendomer gels in good solvents based on a Flory–Huggins type of approach. Using the exact solution for the single tendomer force–extension relation, we calculate the swelling equilibrium of the gels numerically. For the limiting cases of the linear and nonlinear elastic regimes of the tendomer strands, we derive analytic solutions for the equilibrium degree of swelling as a function of the system parameters. We show that the resulting tendomer networks can swell much more than conventional gels and that the preparation conditions can be tuned such that the gels swell predominantly in a linear or a nonlinear response regime. Tendomer gels are also a prototype of a super-soft and practically entanglement-free gel since at preparation state, the tendomers consist mainly of long elastically inactive tails that act as a reservoir of chain segments upon swelling or deformation. This results in a c*-like state at swelling equilibrium for appropriate preparation and swelling conditions. Besides swelling in a good solvent, we also consider the swelling equilibrium of charged tendomer gels. Specific preparation conditions are taken into account in terms of a prestrain coefficient of the network. Monte-Carlo simulations and numerical calculations are performed to test the theoretical predictions. Finally, we discuss a possible route for the synthesis of tendomer gels.