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Dynamics of swollen gel layers anchored to solid surfaces
Maria Gianneli1, Robert F Roskamp2, Ulrich Jonas3
1Max Planck Institute for Polymer Research, P. O. Box 3148, Mainz, 55128, Germany and FO.R.T.H/IESL, P. O. Box 1527, 71110 Heraklion, Greece and Department of Materials Science & Technology, University of Crete, Greece.
Soft Matter
|September 10, 2020
Summary
Researchers studied poly-N-isopropylacrylamide (PNIPAAm) gel layers using dynamic light scattering. They observed two diffusion rates, with faster diffusion increasing with crosslinking density in these surface-attached gels.
Area of Science:
- Polymer Science
- Soft Matter Physics
- Materials Science
Background:
- Poly-N-isopropylacrylamide (PNIPAAm) hydrogels exhibit unique thermoresponsive behavior.
- Understanding the dynamics of surface-attached polymer networks is crucial for applications.
- Ethanol acts as a good solvent for PNIPAAm, influencing swelling and dynamics.
Purpose of the Study:
- To investigate the thermal concentration fluctuations in surface-attached PNIPAAm gel layers swollen in ethanol.
- To characterize the diffusive behavior and its dependence on crosslinking density.
- To compare the dynamics of surface-attached networks with linear PNIPAAm solutions.
Main Methods:
- Dynamic micro light scattering (DLS) technique was employed.
- Analysis of relaxation functions to identify decay times and rates.
- Investigation across a time range from microseconds to seconds.
Main Results:
- Two distinct decay processes were observed in the relaxation function at equilibrium swelling.
- Characteristic rates showed pure diffusive behavior.
- Fast cooperative diffusion increased with crosslinking density due to reduced network mesh size.
- This increase was more pronounced than in linear PNIPAAm solutions.
- Surface attachment and gel inhomogeneities altered network dynamics compared to solutions.
- Slow diffusion in anchored layers was found to be ergodic, unlike conventional gels.
Conclusions:
- Surface-attached PNIPAAm gels in ethanol exhibit complex dynamics with both fast and slow diffusion components.
- Crosslinking density significantly impacts the fast cooperative diffusion, more so than in linear systems.
- Ergodic nature of slow diffusion in anchored layers suggests unique structural properties, though not fully clarified.
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