Polymer gels: Investigation of the swelling induced deformations with a thermodynamically consistent chemo-mechanical model

An increasing demand for adaptive structures using smart materials has emerged in the last decades. These innovative materials are able to meet the required performance of the up-to-date devices improving current systems, especially in the fields of medicine and aerospace. Among adaptive structures, polymer gels are gaining a particular interest due to their similar behavior to that of biological systems. Polymer gels are elastic materials soaked in a fluid that undergo swelling or shrinking when triggered by an external stimulus such as electric field, pH, humidity, temperature. During the swelling or shrinking of the gel, the fluid is absorbed or released, respectively, while large deformations (40-80%) occur. The main applications involving polymer gels are bioinspired microstructures, biological tissues, but also fuel cells and actuators. The effectiveness of polymer gels for adaptive structure applications critically depends on the capability of the gel to achieve both prescribed changes in shape and size within the range of requested performance. Currently, several approaches to perform the shape control of swellable materials are pursued for materials in the form of thin sheets (~10-4m). Furthermore, frequent swelling-deswelling cycles of the gel may generate critical stresses, fracture, and eventually fatigue issues. It is worth noting that fatigue is still a big challenge for polymers.