Supramolecular Gels with Potential Applications as Anti-Icing Agents

Supramolecular gels based on 1,3:2,4-dibenzylidenesorbitol (DBS) with modifications in the <i>para</i> positions of the aromatic rings form effective thickeners for mixtures of monopropylene glycol (MPG) and water, with potential applications as anti-icing fluids. A range of DBS derivatives were tested, and optimal performance was 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 fibers 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 deicing fluid (DF+). Each gelator extended the performance of the deicing 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 takeoff caused breakdown of the gel as desired for the target application. These LMWGs, therefore, significantly improve the performance of deicing fluids and may be useful additives in the formulation of next-generation anti-icing systems.