Dynamics and Structural Evolution in Supramolecular Polymer Networks
Final Report Abstract
The aim of this project was to systematically study the diffusive dynamics and nanostructural relaxation of the building blocks of a model-type set of supramolecular polymer networks. For this purpose, monodisperse and uniform star-shaped polyethylene glycol precursors were equipped with motifs that form supramolecular associates via transition metal complexation with markedly varying strength, controllable by simple choice of the linking metal ion. The nanometer-scale structures of these different supramolecular polymer networks were probed by static light scattering, confirming the presence of just weak nanostructural inhomogeneity. Additional studies by small-angle neutron scattering were also performed and found to be in line with the light-scattering results, but those were not included into any of the four publications that emerged from this project as they covered just part of the samples investigated. In addition to the scattering-based assessment, the dynamics of a 2-% portion of fluorescently labeled polymeric building blocks that diffuse through the gels were monitored by fluorescence recovery after photobleaching (FRAP) on a confocal microscope. These studies have brought unexpected new insight. In particular, it could be discovered how strong the role of connectivity defects in supramolecular (model) networks is. This was seen in FRAP experiments on labeled star-polymers that carry a fluorophore rather than a metal-complexing motif on one of their arm ends, thereby sacrificing their ability to fully contribute to the network matrix connectivity. The connectivity defect created by this circumstance turned out to drastically accelerate their diffusive relocation within the networks. On top of that, a previous finding of unexpected apparent superdiffusive scaling of the time-dependent mean-square-displacement of these tracers as well as such variants that do not create connectivity defects in the networks was confirmed, indicating it to be a universal phenomenon in transient networks. In view of the original focus of this study, the concentration-dependent scaling of the translational diffusion coefficients was found to be in fair qualitative agreement to the Cates–Candau model; it was also found to be in partial agreement to the sticky Rouse model devised by Rubinstein and Semenov. A reason for the not strikingly clear distinction between the models based on this assessment can be that the transient-network architectures probed in our studies are neither a good fit to any of these models. Thus, further work appears to be necessary, based on better model toolkits that closer match either the Cates type or the Rubinstein-Semenov type of supramolecular polymer network architecture. These studies are subject to a sister project that just received funding confirmation by the DFG, which will start in early 2018. This new project will not only continue and tie in to the open ends of the present one, but will also introduce a new prime focus: the potential clustering and bond-lifetime renormalization due to cooperativity of the transient polymer interlinkage points. Together with the insight gained in this present project, these studies have good prospect to synergistically deliver a solid basis for the overall goal of rationally modeling supramolecular polymer-network nanostructural relaxation, mesostructural adaption, and macrostructural self-healing.
Publications
- “Relaxation and Dynamics in Transient Polymer Model Networks.” Macromolecules 2014, 47, 6473–6482
T. Rossow, A. Habicht, and S. Seiffert
(See online at https://doi.org/10.1021/ma5013144) - "Connectivity defects enhance chain dynamics in supramolecular polymer model-network gels." J. Polym. Sci. B: Polym. Phys. 2016, 55, 19–29
A. Habicht, S. Czarnecki, T. Rossow, and S. Seiffert
(See online at https://doi.org/10.1002/polb.24250) - "Self-Diffusion of Associating Star-Shaped Polymers." Macromolecules 2016, 49, 5599–5608
S. Tang, A. Habicht, S. Li, S. Seiffert, and B. D. Olsen
(See online at https://doi.org/10.1021/acs.macromol.6b00959) - “Hybrid Polymer-Network Hydrogels with Tunable Mechanical Response.” Polymers 2016, 8, 82
T. Rossow, S. Czarnecki, and S. Seiffert
(See online at https://doi.org/10.3390/polym8030082)
