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In this paper, we conduct a computational analysis of the effects of initial fixed charge density on the responsive performance of pH-sensitive hydrogels to environmental change in solution pH. The analysis is based on a chemo-electro-mechanical formulation previously termed the multi-effect-coupling pH-stimulus (MECpH) model. In this work, we improve the MECpH model by incorporating the finite deformation formulation into the mechanical equilibrium equation. The present model consisting of coupled nonlinear partial differential equations is solved via a meshless numerical technique called the Hermite-cloud method with the modified Newton iteration methodology. After validation of the MECpH model by comparing the computational results with experimental data available in the literature, several computational case studies are carried out for analysis of the effects of initial fixed charge density on the distributive variations of the diffusive ion concentrations and electric potential and on the deformation of the pH-stimulus-responsive hydrogels, when they are immersed in different buffered solutions.

Abstract:The study of crystal structures in shape memory alloys is of fundamental importance for understanding the shape memory effect. In order to investigate the mechanism of how Cu content affects martensite crystal structures of TiNiCu alloys, the present research examines the atomic displacement of Ti50Ni50−xCux (x = 0, 5, 12.5, 15, 18.75, 20, 25) shape memory alloys using density functional theory (DFT). By the introduction of Cu atoms into TiNi martensite crystal to replace Ni, the displacements of Ti and Ni/Cu atoms along the x-axis are obvious, but they are minimal along the y-and z-axes. It is found that along the x-axis, the two Ti atoms in the unit cell move in opposite directions, and the same occurred with the two Ni/Cu atoms. With increasing Cu content, the distance between the two Ni/Cu atoms increases while the Ti atoms draw closer along the x-axis, leading to a rotation of the (100) plane, which is responsible for the decrease in the monoclinic angle. It is also found that the displacements of both Ti atoms and Ni/Cu atoms along the x-axis are progressive, which results in a gradual change of monoclinic angle and a transition to B19 martensite crystal structure.

Modeling is conducted in this paper for analysis of the influence of Young’s modulus on the response of soft active hydrogels to environmental solution pH changes. A chemo–electro–mechanical formulation termed the multi-effect-coupling pH-stimulus (MECpH) model, which was developed previously according to linear elastic theory for small deformation description, is improved in this paper through incorporation of the finite deformation formulation into the mechanical equilibrium equation. The model is expressed by coupled nonlinear partial differential equations and solved via the meshless Hermite-cloud method with the modified Newton iteration technique. The improved MECpH model is examined by comparison between the computational and published experimental results. Numerical studies are then done on the influence of Young’s modulus on the distributive variations of the diffusive ion concentrations and electric potential, and on the deformation variations of the pH-stimulus-responsive hydrogels within different buffered solutions.