Finite element modeling and design of pH/temperature sensitive hydrogel based biphasic twisting actuators

In this article, a pH/temperature sensitive hydrogel based biphasic twisting actuator is presented and studied in various environmental conditions. The actuator consists of a neutral incompressible elastomeric phase attached to pH/temperature sensitive hydrogel phase which twists, when subjected to pH/temperature variation. The deformation of the actuator depends on the cross-section of the actuator as well as geometrical and environmental parameters. To have a guideline for the design of the biphasic twisting actuator, a finite element model of the mentioned structure is developed. A thermodynamic based constitutive model is used to describe the behavior of the hydrogel. The finite element method is used to resolve the homogeneous and inhomogeneous swelling of the pH/temperature responsive hydrogel to check the validity of the method. Finally, how various parameters affect the torsional behavior of the actuator is discussed in detail. According to the results, to get the maximum twisting angle it is recommended to use the actuator with the square cross-section. Also, the twisting angle can even increase more by decreasing the hydrogel size as well as increasing the length of the actuator.