Ionic Twin Nanostructural Comparison: Propylammonium Butanoate vs. Butylammonium Propanoate and Their Interactions with Water.

This study investigates the nanostructure of two protic ionic liquids (PILs), [N 0 0 0 3 ][C 3 CO 2 ] and [N 0 0 0 4 ][C 2 CO 2 ], with similar polar head groups but varying alkyl chain lengths. An X-ray scattering technique and molecular dynamics simulations have been utilized to characterize the bulk and interfacial properties of these PILs. The findings suggest that the nanostructure of the PILs is primarily determined by the electrostatic forces between charged functional groups playing a dominant role. Despite differences in the alkyl chain lengths, the PILs possess remarkably similar nanostructures. Extending our investigation, we report the impact of water on the nanostructure. Our findings reveal that the addition of water disrupts interactions between cations and anions, weakening Coulombic forces. The disruptive behavior is attributed to the establishment of hydrogen bonds between water and ions. This comprehensive approach provides valuable insights into the nuanced factors shaping the nanostructure of these PILs, which are crucial for tailoring their applications in synthetic chemistry, catalysis, and beyond.