Mechanics of Chemo-Mechanical Stimuli Responsive Soft Polymers

Responsive materials, often obtained by designing the molecular structure of polymers or gels, are able to respond with detectable physical changes to external stimuli of various nature, ranging from chemical (such as pH), temperature, light radiation, magnetic field, mechanical stress, etc. In this paper we propose a micromechanical model, rooted in the statistical approach to the network conformation of polymeric materials, to predict the mechanical response of polymers with embedded responsive molecules. The model makes use of the so-called chains distribution function, aimed at providing the current state of the network’s chains. A univocal relation between the distribution function and the mechanical state of the material is established, so the knowledge of the evolution of such a function with the applied deformation or other external stimuli allows to get the macroscopic response of the material. Finally, the case of responsive molecules inserted into the network as crosslinkers is considered. The responsiveness of the molecules is assumed to depend either on the mechanical and/or chemical stimuli coming from the external environment. The cases involving molecules sensible to chemical stimuli, always imply the presence of a solvent carrying the triggering chemical agent, and thus require to consider the swelling phenomenon induced by the fluid absorbed by the polymer network. The theoretical framework of the micromechanical model is illustrated and some examples are finally presented and discussed.