Effect of Trace Ions on Self-assembly in Ionic Liquids

In our earlier work with cationic surfactants (dodecyltrimethylammonium, DTA+) in ethylammonium nitrate (EAN, an ionic liquid), we found that the critical micelle concentration (CMC) and micelle morphology is sensitive to the choice of surfactant counterion. This is surprising as the nitrate concentration in EAN is ~100 x higher than counterions of added surfactant. Based on stoichiometry, ~99 % of DTA+ surfactant in solution should predominately interact with nitrate regardless of their original counterion. This observed dependency on surfactant counterion highlights that ion specific effects are present, and can be used as an effective tool to regulate self-assembly processes in high ionic strength solutions. The origin of specific ion effect in high ionic strength solutions is not well understood and potentially relates to the anomalous long screening length observed in these solutions. This experiment will examine dodecyltrimethylammonium bromide and nitrate self-assembly in EAN, ethylammonium thiocyanate (EASCN), and ethanolammonium nitrate (EtAN) to reveal the origin of ion specific effects in ILs, as well as their dependency on IL composition and structures.