Modeling of electric‐stimulus‐responsive hydrogels immersed in different bathing solutions

Abstract

By reformulation of the fixed charge density and consideration of finite deformation, a previous model simulating the pH-sensitive hydrogels is refined in this paper for extension to simulating the electric-sensitive hydrogels, which is termed the refined multi-effect-coupling electric-stimulus (rMECe) model. The rMECe model is based on the assumptions: (a) the hydrogel is isotropic and macroscopically homogeneous, (b) all the three phases are incompressible, including the polymeric solid matrix, interstitial water and mobile ions, (c) the effect of electro-osmosis is neglected, (d) bath solution is ideal so that the variation of the activity coefficients with ionic strength can be negligible, i.e., its effect on the concentration profiles is negligible, (e) the smart hydrogel is immersed in an unstirred solution in vibration-free experimental device; the bulk flow of fluid or hydrodynamic velocity can thus be eliminated and subsequently the convective flux is neglected, and (f) the pore of the present hydrogel is narrow enough so that the diffusion dominates the transmission of flux. The model consists of nonlinear coupled partial differential governing equations with the coupling effects of chemo-electro-mechanical multi-energy domains and the fixed charge density with the effect of externally applied electric-field. By comparing the simulating results with experimental data extracted from literature, a very good agreement is achieved and thus this validates the computing accuracy and stability of model. The present rMECe model shows the capability of efficiently predicting the ionic transport and the performance of the hydrogels when they are immersed in a bath solution subject to externally applied electric voltage. The model is used for quantitative analysis of the electric-sensitive hydrogels and for discussion of the influences of several physical parameters on the response of the hydrogels, including the externally applied electric voltage, the initially fixed charge density, and the ionic strength and valence of surrounding solution.

Multiphysics modeling of responsive characteristics of ionic-strength-sensitive hydrogel

“…In other words, as a measure of the ionic concentrations in the solution, the ionic strength is formulated as I ¼ 0:5 In order to further understand the characteristics of the smart hydrogel responsive to the ionic strength in the bathing solution, numerous studies were carried out experimentally, for synthesis of ionic-strength-sensitive hydrogels for wide range of applications (2008; Liu et al 2007;Markland et al 1999;Zhao and Moore 2001), and investigation of the swelling behavior of hydrogels responding to the stimulus of ionic strength (Caykara and Dogmus 2005;Hooper et al 1990). However, few efforts were made on theoretical modeling of ionic-strengthsensitive hydrogel, although there are a large number of published studies on the theory development and simulation of the characteristics of different polyelectrolyte hydrogels (Barrat and Joanny 1996;De and Aluru 2004;De et al 2002;Edgecombe and Linse 2008;Frusawa and Hayakawa 1998;Luo et al 2008;Mann et al 2006;Sommer et al 1994;Vilgis et al 2000;Wallmersperger et al 2001;Yan and De Pablo 2003). Probably, Flory may be the first who introduced the contribution of ionic concentration of the surrounding solution into the swelling of hydrogel (Flory 1953;Flory and Rehner 1943a, b).…”

2D simulation of the deformation of pH-sensitive hydrogel by novel strong-form meshless random differential quadrature method

“…They also conducted the 1D transient analysis of hydrogels subjected to external electric field. Luo et al [24][25][26] studied the responsive behaviour of 1D hydrogel due to the effect of external electric stimulus, solution ionic strength and pH. They also developed the PNP and mechanical equilibrium equations in Lagrangian coordinates, and compared the results with the same set of equations in Eulerian coordinates.…”

Effects of Silica Content on the Properties of Poly(N-isopropylacrylamide) / Silica Nanocomposite Hydrogels

“…Due to its particular feedback system [1], that hydrogel can show significant changes in shapes and volumes as a response to variation of external stimuli such as temperature [2], pH [3] and electric field [4], hydrogels have gained its popular application in numerous fields such as biomaterials [5] and sensing applications [6]. Poly(N-isopropylacrylamide)( PNIPA) is a representative thermosensitive polymer with a lower critical solution temperature(LCST) around 34 o C [7], a specific temperature at which the polymer shows phase separation.…”