Thermo-mechanical properties of macromolecular materials
The fast developments in the synthetic chemistry during the last decades have made possible the preparation of a large variety of macromolecules with controlled topology and functionality. Our work is focused on understanding the relation between the molecular architecture, composition and processing on one hand and the morphology and thermo-mechanical properties of macromolecular materials on the other hand. Such understanding is not only of fundamental interest, but will also help to predict the properties and design new materials for specific applications. In this endeavor we cooperate extensively with synthetic chemistry partners. Commonly studied systems include photo-responsive polymers, nanocomposites, synthetic and biological gels.
For example, recently we prepared CNT–hydrogel composites by in situ polymerization of poly(ethylene glycol) (PEG) around a preformed carbon nanotube (CNT) meshwork. We found that the composites facilitate long-term survival and differentiation of neural stem cells. The formation of the CNT meshwork was studied by monitoring the frequency (ω) dependence of the real (G′) and imaginary (G″) parts of the complex shear moduli of gel precursors (PEG solutions) with different CNT content. The frequency response of the precursor of pure PEG hydrogels reveald non-Newtonian liquid behavior, characterized by a terminal region with G′(ω) ~ ω2, G″(ω) ~ ω1. Upon incorporating smal fraction of CNTs, a plateau with G′ > G″ was observed at low frequencies, indicating the formation of weak CNTs percolation meshwork. At higher CNT content, G′ > G″ over a wider range of frequency reflecting the response of a strong CNTs meshwork. After PEG crosslinking, this meshwork is preserved in the final composites.
Left: Schematic illustration of the preparation of CNT–PEG hydrogel composites. The CNTs were ground in 1-hexyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) imide. Poly(ethylene glycol) diacrylate with a photoinitiator was added to the mixtures and they were used as precursors. The precursors were sandwiched between two glass slides with two cover slides used as spacers. The CNT–PEG hydrogel composites with varying CNT content were prepared by UV-induced polymerization followed by solvent replacements. Right: frequency (ω) dependence of the G′ (black) and G″ (green) for gel precursors (PEG solutions) with a CNT content of: 0 (squares), 5 (circles) and 20 (rombi) arbitrary units.
In another example, in close cooperation with Si Wu (MPIP and USTC in Hefeie, China) we studied the photoinduced solid-to-liquid transition in azobenzene-containing polymers. The temperature dependences of the shear moduli G' and G'' clearly show that the glass temperature (Tg) of cis-azopolymers is well below the room temperature, while the Tg of trans-azopolymers is well above the room temperature. Furthermore, we found that the length of the spacer between the polymer backbone and the azobenzene group on the side chain has major influence on thephotoinduced solid-to-liquid transition.
Left: Photographs and chemical structures of the studied azopolymers. Right: Temperature dependence of the storage modulus (G′, black squares) and the loss modulus (G′′, red circles) for a cis-P-12-Azo during first cooling, first heating and the second cooling cycles. Note that during heating, the cis-P-12-Azo thermally switched to trans-P-12-Azo.
1.
Ye LJ, Ji HC, Liu J, Tu CH, Kappl M, Koynov K, Vogt J, Butt HJ.
Carbon Nanotube-Hydrogel Composites Facilitate Neuronal Differentiation While Maintaining Homeostasis of Network Activity
Advanced Materials, 2021, 33, 2102981
2.
Han JX, Xie CM, Huang YS, Wagner MF, Liu WD, Zeng XL, Liu JH, Sun SJ, Koynov K, Butt HJ, Wu S.
Ru-Se Coordination: A New Dynamic Bond for Visible-Light-Responsive Materials
Journal Of The American Chemical Society, 2021, 143, 12736-12744
3.
Agasty A, Wisniewska A, Kalwarczyk T, Koynov K, Holyst R.
Macroscopic Viscosity of Polymer Solutions from the Nanoscale
ACS Applied Polymer Materials, 2021, 3, 2813-2822
4.
Singh M, Hu M, Cang Y, Hsu H-P, Therien-Aubin H, Koynov K, Fytas G, Landfester K, Kremer K.
Glass Transition of Disentangled and Entangled Polymer Melts: Single-Chain-Nanoparticles Approach
Macromolecules, 2020, 53, 8562-8569
5.
Tee H, Zipp R, Koynov K, Tremel W, Wurm F.
Poly(methyl ethylene phosphate) hydrogels: Degradable and cell-repellent alternatives to PEG-hydrogels.
European Polymer Journal, 2020, 141, 110075
6.
Weis P, Hess A, Kircher G, Huang S, Auernhammer G, Koynov K, Butt H-J, Wu S.
Effects of Spacers on Photoinduced Reversible Solid-to-Liquid Transitions of Azobenzene-Containing Polymers.
Chemistry - A European Journal, 2019, 25, 10946-10953
7.
Zhou Y, Chen M, Ban Q, Zhang Z, Shuang S, Koynov K, Butt H-J, Kong J, Wu S.
Light-Switchable Polymer Adhesive Based on Photoinduced Reversible Solid-to-Liquid Transitions.
ACS Macro Letters, 2019, 8, 968-972
8.
Tee T, Koynov K, Reichel T, Wurm F.
Noncovalent Hydrogen Bonds Tune the Mechanical Properties of Phosphoester Polyethylene Mimics.
ACS Omega, 2019, 4, 9324-9332
9.
Pipertzis A, Hess A, Weis P, Papamokos G, Koynov K, Wu S, Floudas G.
Multiple Segmental Processes in Polymers with cis and trans Stereoregular Configurations.
ACS Macro Letters, 2018, 7, 11-15
10.
Alexandris S, Franczyk A, Papamokos G, Marciniec B, Graf R, Matyjaszewski K, Koynov K, Floudas G.
Dynamic Heterogeneity in Random Copolymers of Polymethacrylates Bearing Different Polyhedral Oligomeric Silsesquioxane Moieties (POSS).
Macromolecules, 2017, 50, 4044-4054
11.
Zhou H, Xue C, Weis P, Suzuki Y, Huang S, Koynov K, Auernhammer G, Berger R, Butt H-J, Wu S.
Photoswitching of glass transition temperatures of azobenzene-containing polymers induces reversible solid-to-liquid transitions.