The hierarchical bulk molecular structure of poly(acrylamide) hydrogels: beyond the fishing net

Abstract

The polymeric structure of hydrogels is commonly presented in the literature as resembling a fishing net. However, this simple view cannot fully capture all the unique properties of these materials....

Transpiration through hydrogels

“…This is based on the estimate that for many natural porous media the length scale l is related to the permeability K by l 2 ≈ 10 2 K. For example, Cubaud & Ho (2004) find l 2 = 28.43K for square channels. This estimate of permeability and corresponding pore size appears reasonable, as Gombert et al (2020) report hierarchical structures in polyacrylamide hydrogels with features up to 100 nm size.…”

“…This estimate of permeability and corresponding pore size appears reasonable, as Gombert et al. (2020) report hierarchical structures in polyacrylamide hydrogels with features up to 100 nm size.…”

“…This is of the same order of magnitude as the size of larger features of a hydrogel structure proposed by Gombert et al. (2020) (100 nm). The fit parameters correspond to a poroelastic time scale (3.18) of 4 d. Thus, with the dimensionless times predicted by the model for typical transitions (see figure 8), , the model predicts transition times between 0.08 and 0.16 d. While this is somewhat smaller that the experimentally observed transition times (0.26–1.2 d) for these datasets, the prediction is of the correct order of magnitude.…”

Charge‐Induced Structural Changes of Confined Copolymer Hydrogels for Controlled Surface Morphology, Rheological Response, Adhesion, and Friction

“…The smallest structure consists of clusters of bis‐AAm with a size smaller than 4 nm, which agglomerate into domains that can grow to hundreds of nm and micron in size with increasing bis‐acrylamide concentration and are interconnected by polymer chains. [ 18 ] At the selected crosslinker concentration here (Table 1), that previous work observed clusters 100s of nm in size based on X‐ray scattering. We emphasize that these explicit domains are not clearly observed in free‐swelling PAAm hydrogels, perhaps due to the non‐uniform and large swelling, which made imaging challenging.…”

“…Recent work by Gombert et al. [ 18 ] has revealed that the difference between the polymerization kinetics of bis‐acrylamide and acrylamide leads to a hierarchical structure in PAAm hydrogels. The smallest structure consists of clusters of bis‐AAm with a size smaller than 4 nm, which agglomerate into domains that can grow to hundreds of nm and micron in size with increasing bis‐acrylamide concentration and are interconnected by polymer chains.…”