A Thermodynamically Consistent Electro-Chemo-Hydro-Mechanical Model for Smart Polymers

Smart polymers are stimuli-responsive materials that undergo reversible and large changes of the material properties as a consequence of small environmental variations. Their light weight, biocompatibility, adaptability, mechanical strength and environment-friendly properties make them suitable for a wide range of applications, such as actuators, sensors and energy transducers. Despite their very interesting properties, there are still many problems which need to be solved. In particular, there is a high demand by the scientific community to develop advanced theoretical models which aim at understanding the complex and unclear phenomena occurring in smart polymers. In the present thesis, an innovative multiphysics electro-chemo-hydro-mechanical (ECHM) model is formulated within the framework of continuum mechanics. The proposed model assumes the solvent-ion-polymer mixture as a continuum homogenized body and takes into account four different physical fields, namely: (i) the electrical field, (ii) the chemical field related to the ion transport, (iii) the chemical field related to the water/solvent transport, and (iv) the mechanical field within the framework of large deformations. Couplings terms are derived at the constitutive level among the involved physical fields and allow to model a key aspect of smart polymers, i.e. the capability of transducing energy from one form to another. Reduced versions of the ECHM model are used to investigate, numerically and analytically, three particular problems involving smart polymers, namely: (i) the chemical reactions occurring at the interface between the polymer membrane and the electrodes of electrochemical cells, (ii) the electro-chemo-mechanical state of a single polymeric membrane within a stack of membranes, and (iii) the swelling/shrinking process of constrained and stressed polymer gels. The performed investigation confirm that the ECHM model and its reduced versions are capable of describing the complex multiphysics behavior of smart polymers. The current ...