Coupled thermo-mechanical swelling of a thermo-responsive hydrogel hollow cylinder under extension-torsion: Analytical Solution and FEM

Abstract

In this article, the mechanical swelling behavior of poly-(N-isopropylacrylamide) hydrogel is scrutinized considering a hollow circular cylinder subjected to temperature variation-extension-torsion. Accordingly, an analytical solution is presented to consider the general combined loading on temperature-sensitive hydrogel cylinder for two approaches, considering same temperature for whole structure and solving heat equation to compute internal temperature of structure. Additionally, to evaluate the proposed solution, finite element analysis has been conducted for same problem which revealed excellent conformity for various case studies. Therefore, a user-material subroutine, UHYPER, is implemented to be employed in finite element analysis in order to define swelling of PNIPAM hydrogels. This subroutine was validated using free swelling and constraint swelling with previous and their analytical solutions. Regarding the complexity of material and loading namely, nonlinear finite behavior of hydrogel as well as combined cooling-extension-torsional loading, various factors, cross-linked density, axial stretch, torsional twist and temperature variation, were investigated to clarify the swelling behavior of hydrogel. Solving heat equation, in the second approach, enables us to apply various thermal conditions on this structure, while in previous studies, the temperature of whole structure is considered to vary simultaneously with the same function. This approach can help researchers to examine diverse thermo-mechanicals problem for temperature-sensitive hydrogels.

Swelling Modelling and Kinetics Investigation of Polymer Hydrogel Composed of Chitosan-g-(AA-AM)

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Programmable self-folding of trilayer and bilayer-hinge structures by time-dependent swelling of tough hydrogels

“…Hydrogels are three-dimensional polymeric networks that can absorb and expel a huge amount of solvent under external stimuli (Niroumandi et al, 2021a; Shojaeifard and Baghani, 2020) which in turn causes the hydrogel to swell or shrink. Due to the swelling and de-swelling of hydrogels, these materials undergo considerable volume change under a change in external stimuli, including temperature, pH, light intensity, ion concentration, electric and magnetic fields (Kasinathan and Srinivasan, 2018; Shojaeifard and Baghani, 2019; Shojaeifard et al, 2019a, 2019b, 2021). Although conventional hydrogels have various merits to be utilized in diverse applications (Bin et al, 2021; Guenther et al, 2009; Niroumandi et al, 2021b, 2022), the composition of inhomogeneous networks and low polymer content make the hydrogels mechanically weak.…”

Transient swelling of cylindrical hydrogels under coupled extension-torsion: Analytical and 3D FEM solutions

“…Employing a UHYPER subroutine, developed in the finite element method (FEM) framework, they showed that their proposed solution has an excellent agreement with FEM results. In another work, Shojaeifard et al (2021) proposed a coupled solution for the same problem, while the temperature distribution was solved simultaneously. Again, their solution was only acceptable for the equilibrium behavior of the hydrogel.…”