Mechanics of active mechano-chemical responsive polymers

The need for smart materials in advanced applications, has promoted significantly the research in the field of responsive (or active) materials. They are capable of some physical response to external stimuli, such as temperature, pH, light, mechanical stress, etc. so they can adapt themselves to the surrounding environment. In the present paper, we propose a mechanical model to describe the response of polymers containing mechanically responsive molecules (mechanophores), having the ability to assume two distinct geometrically stable configurations under mechanical actions or due to a change of the environment’s pH. When linked to the polymer’s chains, under a proper mechanical stress, they switch from one state to the other, triggering a macroscopic deformation of the material. Such an internal deformation, driven by the mechanophores’ activation, can be exploited to get a desired functionality of the polymer. Our model starts from the mechanical behavior at the microscopic level, and through the mechanics of a single chain and chain statistics, it is scaled-up to the (mesoscopic) continuum level. An energy-based approach is adopted: the free energy W is obtained by adding up the contribution of the network deformation (), of the mixing term related to the solvent uptake () and of the switching of the hosted responsive molecules (). Numerical simulations demonstrate that the material response under chemical or mechanical stimuli, shows a permanent deformation due to the activation of the switchable molecules, enabling the design of smart self-adaptive polymers.