Chemistry for sustainable building materials

We are proud to highlight another publication by Prof. Dr. Oliver Weichold. Together with Pia B. Sassmann, he co-authored the study Synergistic effects in cross-linked blends of ion-conducting PEO-/PPO-based unsaturated polyesters, which presents an innovative approach to enhancing ion conductivity.

In this work, unsaturated polyesters (UP) based on poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized, doped with lithium perchlorate (LiClO₄), and cross-linked with styrene using a redox initiator. The findings reveal distinct behaviors in conductivity between PEO- and PPO-based polyester networks. While the conductivity decreases with increasing molecular weight for PEO, the opposite trend is observed for PPO.

Remarkably, the study discovered that targeted blending and cross-linking of PEO- and PPO-based polyesters can create synergistic effects. A 1:1 blend of short-chain PPO and long-chain PEO exhibited a resistivity five times lower than pure PEO and three times lower than pure PPO. These effects are attributed to enhanced chain mobility and intrachain hopping mechanisms, which are amplified by the cross-linking process.

Beyond improved ion conductivity, these networks offer rubber-like elasticity and high water tolerance, making them suitable for diverse applications, particularly under mechanical stress, in atmospheric conditions, or even in aqueous environments where standard ion-conducting systems often fail.

Sassmann, P.B., Weichold, O.
Synergistic effects in cross-linked blends of ion-conducting PEO-/PPO-based unsaturated polyesters
Ionics 27, 3857–3867 (2021). https://doi.org/10.1007/s11581-021-04149-z

A recent publication in Soft Matter (Issue 40, 2018) introduces a novel highly alkaline hydrogel designed to restore the alkaline buffer capacity in carbonated cementitious materials. This property is essential for preventing steel corrosion in reinforced concrete.

The hydrogel is based on a copolymer of diallyldimethylammonium hydroxide (DADMAOH) and methacrylamide. The addition of methacrylamide as a co-neutral monomer allows for extensive tunability of the gel’s rheological properties. The viscosity increases a thousandfold—from 0.35 Pa s to over 350 Pa s—when 10 mol% methacrylamide is used, showcasing the material’s adaptability.

1. Ion Exchange: Experiments demonstrated efficient diffusion of hydroxide ions from the hydrogel into carbonated material, accompanied by the release of carbonate ions.
2. Re-Alkalisation: The gel’s effectiveness was confirmed through the phenolphthalein test (DIN EN 14630:2007-01) and IR spectroscopy.
3. Universal Applicability: The gel can be applied both for modern infrastructure maintenance and the preservation of historical monuments.

Jung, A.; Weichold, O.
Preparation and characterisation of highly alkaline hydrogels for the re-alkalisation of carbonated cementitious materials
Soft Matter 2018, 14 (40), 8105–8111. https://doi.org/10.1039/c8sm01158c.