Effect on aggregation behavior of long-chain spacers of dicationic imidazolium-based ionic liquids in aqueous solution

• Aggregation behavior of dicationic ionic liquids (ILs) with different spacers was evaluated.
• ILs with long spacers are able to change their conformation at the interface.
• Aggregates showed different morphologies with increase in concentration.
• Dicationic ILs tend to form aggregates with better packing than monocationic ILs.
• Longer free alkyl chain is not a required structural feature for the use of dicationic ILs in applications such as surfactants.

A systematic study was done in order to evaluate the aggregation behavior of long-chain spacers of dicationic imidazolium-based ionic liquids (ILs) in aqueous solution. The influence of spacer chain length on the self-aggregation of ILs was investigated with surface tension, conductivity, fluorescence, differential scanning calorimetry (DSC), dynamic light scattering (DLS), and transmission electron microscopy (TEM) experiments. The critical aggregation concentration (CAC) of ILs obtained from the different techniques indicated good agreement. Surface tension measurements showed that increasing the length of the spacer group improves the surfactant properties, as previously hypothesized. Aggregates with different morphologies were detected. The aggregation behavior of dicationic ILs was also compared with analogous monocationic ILs. It was observed that dicationic ILs tended to form aggregates with more structured packing than analogous monocationic ILs.

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