Berlin 2015 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: P7: Hydrogels and Elastomers

CPP 35.2: Poster

Dienstag, 17. März 2015, 14:00–16:00, Poster C

The Formation and Swelling of Superabsorbent Networks: A Monte Carlo Study — •Michael Lang, Andreas John, and Jens-Uwe Sommer — Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany

The free-radical polymerization was studied in aqueous acrylic acid solution in the presence of cross-linkers using the Bond Fluctuation Model (BFM). Network formation was analyzed for varying cross-linker reaction rates, cross-linker composition and number fraction, cross-linker functionality and time dependent initiator release. For all simulations we observe an auto-acceleration of reaction kinetics similar to the gel effect but independent of the degree of cross-linking. The weight distributions of chains that result from reactions of one radical and the number distribution of cross-linkable sites on these chains can be approximated by Poisson distributions. The weight fractions of the active material and gel, the average strand length within the active material, and the gel point are determined. The swelling behavior of neutralized networks seems to confirm the Flory-Rehner prediction for the equilibrium degree of swelling as function of the average strand length. However, a more detailed investigation reveals that this results from the fortuitous cancellation of corrections due to inactive material and entanglements for networks with a structure similar to our study. Thus, only the networks with a rather large active strand length agree with the Flory-Rehner model, while the networks with a short elastic strand length show an additional non-affine contribution to the equilibrium degree of swelling.