This
work presents an experimental study of the network structure
of swollen, charged hydrogels. We provide an in-depth comparison of
two proton low-field NMR methods, i.e., transverse relaxation and
double-quantum spectroscopy, that are both sensitive to residual orientation
correlations of the network chain segments. The results are in both
cases analyzed by help of integral inversion techniques, and both
methods are demonstrated to provide comparable results despite the
more qualitative nature of the transverse relaxation. We investigate
model samples that are similar to commercial superabsorber materials
based on partly neutralized and chemically cross-linked poly(acrylic
acid) as prepared by free radical polymerization. The degree of cross-linking
and the monomer concentration are varied during synthesis. Both parameters
are found to affect the network structure and the amount of elastically
inactive defects in a systematic way, and a comparison with commercial
samples with homogeneous or purposely inhomogeneous core–shell
structures proves that the cross-linking bimodality of the latter
is readily revealed despite the rather large intrinsic inhomogeneity
of the swollen gels.
Desalination of a sodium chloride solution is achieved by the incorporation of salt depleted water into an acrylic acid based hydrogel and the subsequent deswelling of the gel by mechanical force to gain water with a lower salt content. This is a new approach towards the problem of desalination of seawater that has, to the best of our knowledge, not been presented before. In a proof-of-principle experiment the salt content of a 10 g/L NaCl solution could be reduced by 35% in one cycle. The influence of main chemical parameters, e.g. degree of crosslinking, degree of neutralization and experimental parameters like particle size and salt concentration on the desalination process are examined. Possible optimum conditions for the desalination using a poly(acrylic acid) network are discussed and the construction of a simple apparatus for deswelling by mechanical force is described.
The development of sophisticated synthetic routes for polymeric materials and more complex formulation used in current polymers require more advanced analytical techniques. A direct correlation between molar mass distribution and chemical composition is provided.
A universal alignment medium for the measurement of anisotropic NMR parameters that can be used for almost any type of sample would be highly useful for structure analysis in solution. Cross‐linked poly(ethylene oxide) with incredible solvent and solute compatibility range provides this medium. The picture shows residual 15N chemical shift anisotropies (RCSAs) of 15N‐labeled ubiquitin.
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