title: Solvent and solute ingress into hydrogels resolved by a combination of imaging techniques.
abstract: Using simultaneous neutron, fluorescence, and optical brightfield transmission imaging, the diffusion of solvent, fluorescent dyes, and macromolecules into a crosslinked polyacrylamide hydrogel was investigated. This novel combination of different imaging techniques enables us to distinguish the movements of the solvent and fluorescent molecules. Additionally, the swelling or deswelling of the hydrogels can be monitored. From the sequence of images, dye and solvent concentrations were extracted spatially and temporally resolved. Diffusion equations and different boundary conditions, represented by different models, were used to quantitatively analyze the temporal evolution of these concentration profiles and to determine the diffusion coefficients of solvent and solutes. Solute size and network properties were varied and their effect was investigated. Increasing the crosslinking ratio or partially drying the hydrogel was found to hinder solute diffusion due to the reduced pore size. By contrast, solvent diffusion seemed to be slightly faster if the hydrogel was only partially swollen and hence solvent uptake enhanced.
authors.affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, 40225 Düsseldorf, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Wagner
authors.affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, 40225 Düsseldorf, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Burbach
authors.affiliation: Neutron Imaging and Activation Group, Paul Scherrer Institute, 5232 Villigen, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Grünzweig
authors.affiliation: Neutron Imaging and Activation Group, Paul Scherrer Institute, 5232 Villigen, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Hartmann
authors.affiliation: Neutron Imaging and Activation Group, Paul Scherrer Institute, 5232 Villigen, Switzerland.
authors.forename: E
authors.initials: E
authors.lastname: Lehmann
authors.affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, 40225 Düsseldorf, Germany.
authors.forename: S U
authors.initials: SU
authors.lastname: Egelhaaf
authors.affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, 40225 Düsseldorf, Germany.
authors.forename: H E
authors.initials: HE
authors.lastname: Hermes
mesh_terms: D004058:Diffusion; D020100:Hydrogels / Q000737:chemistry*; D008956:Models, Chemical; D010316:Particle Size; D012997:Solvents / Q000737:chemistry
chemical_list: D020100:Hydrogels; D012997:Solvents