Mechanical and Transport Properties of the Poly(ethylene oxide)−Poly(acrylic acid) Double Network Hydrogel from Molecular Dynamic Simulations

Abstract

We used atomistic molecular dynamics (MD) simulations to investigate the mechanical and transport properties of the PEO-PAA double network (DN) hydrogel with 76 wt % water content. By analyzing the pair correlation functions for polymer-water pairs and for ion-water pairs and the solvent accessible surface area, we found that the solvation of polymer and ion in the DN hydrogel is enhanced in comparison with both PEO and PAA single network (SN) hydrogels. The effective mesh size of this DN hydrogel is smaller than that of the SN hydrogels with the same water content and the same molecular weight between the cross-linking points (M c ). Applying uniaxial extensions, we obtained the stress-strain curves for the hydrogels. This shows that the DN hydrogel has a sudden increase of stress above ∼100% strain, much higher than the sum of the stresses of the two SN hydrogels at the same strain. This arises because PEO has a smaller M c value than PAA, so that the PEO in the DN reaches fully stretched out at 100% strain that corresponds to 260% strain in the PEO SN (beyond this point, the bond stretching and the angle bending increase dramatically). We also calculated the diffusion coefficients of solutes such as D-glucose and ascorbic acid in the hydrogels, where we find that the diffusion coefficients of those solutes in the DN hydrogel are 60% of that in the PEO SN and 40% of that in the PAA SN due to its smaller effective mesh size.

Hydrogels for Soft Machines

“…Molecular dynamics simulations have been carried out for these PEO-PAA gels, and show that the elastic modulus rises suddenly at strains of about 100%, where the first network becomes fully stretched. [69] This combination of high stress with a large strain to break increases the fracture toughness.…”

A molecular dynamics investigation of the deformation mechanism and shape memory effect of epoxy shape memory polymers

“…MD simulations can also consider the vibrational modes of individual atoms and calculate many fundamental atomic interactions at the individual chain level, which cannot be obtained by other numerical simulation methods, such as the finite element method. For example, Jang et al [29] used MD simulations to investigate the mechanical and transport properties of a poly(ethylene oxide)-poly(acrylic acid) double network hydrogel with 76 wt% water content. Li et al [30] extensively characterized the thermomechanical response of a thermoset polymer composed of epoxy EPON862 and curing agent Diethyltoluenediamine (DET-DA) using MD simulations.…”

Novel Micro/nanostructures from a Double Network Gel

“…Gong et al studied the mechanism to account for the toughness of the DN gel through experiments and theories. [10][11][12][13] But the mechanism is not clearly understood until now because it is difficult to study the microstructure of DN gels. To address this problem, here we develop a new method to study the microstructure of DN gels easily.…”