Recent Advances of the Constitutive Models of Smart Materials — Hydrogels and Shape Memory Polymers

Abstract

Hydrogels and shape memory polymers (SMPs) possess excellent and interesting properties that may be harnessed for future applications. However, this is not achievable if their mechanical behaviors are not well understood. This paper aims to discuss recent advances of the constitutive models of hydrogels and SMPs, in particular the theories associated with their deformations. On the one hand, constitutive models of six main types of hydrogels are introduced, the categorization of which is defined by the type of stimulus. On the other hand, constitutive models of thermal-induced SMPs are discussed and classified into three main categories, namely, rheological models; phase transition models; and models combining viscoelasticity and phase transition, respectively. Another feature in this paper is a summary of the common hyperelastic models, which can be potentially developed into the constitutive models of hydrogels and SMPs. In addition, the main advantages and disadvantages of these constitutive modes are discussed. In order to provide a compass for researchers involved in the study of mechanics of soft materials, some research gaps and new research directions for hydrogels and SMPs constitutive modes are presented. We hope that this paper can serve as a reference for future hydrogel and SMP studies.

Theoretical and Numerical Analysis of Mechanical Behaviors of a Metamaterial-Based Shape Memory Polymer Stent

“…Thus hyperelastic constitutive models are used to charaterize their materails properties. For the SMP stent material, a series of constitutive models are developed to describe the unique thermo-mechanical behavior [41,42]. Nevertheless, most constitutive models are confined with describing large deformation of SMPs or complex expressions [43][44][45][46].…”

Study on Large Deformation Behavior of Polyacrylamide Hydrogel Using Dissipative Particle Dynamics

“…Therefore, we compare our simulation results with current constitutive theory of polymers to reveal the underlying mechanism of the large deformation behavior of PAAm hydrogel. In current constitutive theory (Huang et al, 2020), two key parts, i.e., the free energy of a single chain and the statistical sum of the free energy of all chain, are crucial to bridge the mesoscale chain conformation change to the bulk mechanical response of hydrogels. Considering the polymer chains in our DPD simulations are close to the so-call freely joint chains, the Langevin chain model is adopted to characterize the free energy of a single chain…”

Mechanical response and equilibrium swelling of thermoresponsive copolymer hydrogels

“…where the coefficients χ 0 and χ 1 evolve linearly with T or T −1 . 16,17 A constitutive framework for the analysis of solvent transport and the mechanical response of TR gels under three-dimensional deformations with finite strain grounded in Eqn (1) was developed in references; [18][19][20][21][22] see recent reviews by Liu et al 23 and Huang et al 24 A phenomenological approach to the description of equilibrium swelling of TR gels based on the Landau theory of phase transition was proposed by Drozdov. 25,26 A model for equilibrium swelling of TR gels, where the Flory expression for the specific energy of interaction between monomers and solvent molecules was replaced with more sophisticated relations based on the double lattice concept, was developed by Lee and Bae.…”