Supramolecular Gels with Potential Applications as Anti-Icing Agents

Supramolecular gels based on 1,3:2,4-dibenzylidenesorbitol (DBS) with modifications in the para positions of the aromatic rings form effective thickeners for mixtures of monopropyleneglycol (MPG) and water, with potential applications as anti-icing fluids. A range of DBS derivatives were tested and optimal performance observed for DBS, DBS-OCH3 and DBS-SCH3. Notably, DBS-SCH3 formed gels at concentrations nearly 10-fold lower (<0.1% wt/vol) than DBS or DBS-OCH3, which may be of use in a range of applications. As the amount of water added to MPG increased, gelation ability, gel thermal stability and rheological stiffness improved as gelator solubility decreased and a solvophobically-driven ‘solid-like’ gel network was more easily formed. However, once the water content reached a critical level, gelator solubility became too low and gelation was prevented. DBS-OCH3 could tolerate more water than DBS, owing to its higher polarity. The gelators assembled into networks composed of fibres ca. 5-10 nm in diameter. On thermodynamically-controlled slow cooling, DBS-SCH3 formed a microcrystalline tape-like morphology, but on faster kinetically-controlled cooling, more typical of the proposed application, DBS-SCH3 assembled into the preferred nanoscale fibrillar network. The gelators were tested in a commercially available aviation de-icing fluid (DF+). Each gelator extended the performance of the de-icing fluid in a water spray endurance test, and in some cases, provided ‘holdover times’ expected for a higher performance anti-icing fluid. Performance was dependent on gelator loading and the dilution of the DF+ fluid – importantly, holdover times increased with dilution as gel assembly was promoted, indicating that DBS additives may allow the typical amounts of MPG used in such fluids to be lowered. Levels of strain typical of those experienced on aircraft take-off caused breakdown of the gel. These LMWGs therefore significantly improve the performance of de-icing fluids and may be useful additives in the formulation of next generation anti-icing systems.