Kinetics of Swelling of Cylindrical Temperature-Responsive Hydrogel: A Semi-Analytical Study

Abstract

Cylindrical hydrogels have a wide variety of applications, especially in microfluidics as micro-valves, micro-mixers, and micro-lenses. Main advantages of them can be mentioned as their simple geometry and autonomous functionality due to their responses to the environmental stimuli. In current research, kinetics of swelling, shrinking and force generation of cylindrical temperature-responsive hydrogels have been investigated analytically. According to this, models of fluid permeation and large deformation of the hydrogels were considered and an analytical solution was performed. In order to study the behavior of the cylindrical hydrogels, the temperature is changed between higher and lower of the phase transition temperatures, and kinetics of the swelling and shrinking of the hydrogel have been studied and the distribution of stresses, stretches, water concentration and chemical potential are presented throughout the process. In addition, to investigate the behavior of the actuators, the cylindrical hydrogel is placed inside a hollow permeable pillar and the pressure of the hydrogel which puts on the pillar is studied. Ultimately, a comprehensive study on the effects of different parameters, namely, amount of temperature change, cross-link density and geometry, is conducted and the results are presented, which can be utilized in the design procedures of such actuators.