One-Way Diffusion of Ionic Liquids in a Mixing Process with Water

• DOI: 10.7566/jpsj.85.093001
• Publication Date: 2016-08-03T01:04:08Z
• Authors: Noriko Oikawa; Daiki Tahara; Rei Kurita
• Keywords: 02 engineering and technology; 0210 nano-technology; 01 natural sciences; 0104 chemical sciences

In contrast to the usual diffusive mixing process between two miscible liquids, the ionic liquid [Cnmim][PF6] forms a droplet in water while mixing. The droplet retains a sharp interface with surface tension, gradually decreasing in size until completely mixed with water. This peculiar behavior in the mixing process accompanies one-way diffusion, in which ions diffuse in one direction only from the bulk IL droplet into the bulk continuum of water. The activation energy of the one-way diffusion at the [Cnmim][PF6]/water interface increases with increasing length of the hydrophobic alkyl chains attached to the cation molecules of [Cnmim][PF6]. It is considered that the hydrophobic nanoscale structure observed in [C4mim][PF6] plays an important role in the generation of the droplet and the mixing dynamics.