Mechanism of High Hydrocarbon-Fuel-Gelation Performance of Ultralow-Concentration Bis-urea-Based Gellants

Bis-urea-based gellants have garnered considerable attention due to their capacity to form all kinds of gels in solvents for multiple applications. Nevertheless, the range of applicable solvents is limited, and the synthesis process is complicated. Herein, we report a one-step synthesis process of bis-urea-based gellants (Bu(<i>n</i>)) for gelling nonpolar organic solvents, including high-energy fuels. Importantly, the critical gelation concentration (CGC) of Bu(<i>n</i>) decreases with the increase of alkyl chain length, and that of Bu18 is lower than 0.1 wt % in various hydrocarbon fuels. The discrepant gelation performance of gellants in solvents was investigated by molecular dynamics simulation and spectral characterizations. The results indicate that the electrostatic interaction between urea groups is vital to constructing a gellant framework, and the wide van der Waals (vdW) surface provided by alkyl groups helps to immobilize solvents. The nonbonding interactions between gellant molecules facilitate the formation of a 3D fibrous network structure, which further accumulates into a cambium layer structure. Due to the excellent gelation performance of gellants in fuels, the gel fuels perform the rheological characteristics of shear thinning and thixotropic recovering with calorific value remaining, thus demonstrating potential for application.