Investigating the behavior of temperature-responsive hydrogels by considering functionally graded properties

Abstract

Todays, hydrogels have attracted many researchers due to their unique properties in responding to exterior stimuli and swelling-induced by water absorption. According to their reversible swelling, it is important to predict their mechanical response. The functionally-graded temperature-sensitive hydrogel is one of the most applicable materials in industry. Thus, to study the mechanical behavior of these materials, an energy density function is introduced which includes network stretch energy and mixing part. Then, considering functionally-graded properties along the thickness, bending of FG temperature-sensitive hydrogels is solved analytically under plane-strain assumption. Verifying the presented analytical procedure, the results are compared with outcomes of finite-element-method. To solve diverse problems by finite-element-method, UHYPER subroutine has been written and verified in free-swelling problem. Next, the radius, radial stress and tangential stresses are studied by both methods for FG temperature-sensitive hydrogels. Finally, according to the importance of factors such as semi-angle and bending curvature in the industrial designs, these factors are investigated by changing the temperature in range of 320 to 288. Results demonstrate the capability of these material to be implemented in sensors and actuators. In addition, the continuity of stresses field is the other reason of utilizing FG hydrogels, while the multi-layer hydrogels do not have continuous stress fields.