Ethylammonium nitrate in high temperature stable microemulsions

Abstract

The increasing no. of publications reflects the still growing interest in nonaq. microemulsions contg. room-temp. ionic liqs. Recently, we characterized microemulsions composed of the room-temp. ionic liq. ethylammonium nitrate (EAN) as polar phase, dodecane as continuous phase and 1-hexadecyl-3-Me imidazolium chloride ([C16mim][Cl]), an IL that exhibits surfactant properties, and decanol as cosurfactant at ambient temp. We demonstrate here the high thermal stability of these microemulsions. Along an exptl. path, no phase change could be obsd. visually within a temp. range between 30 °C and 150 °C. The microemulsions are characterized with quasi-elastic light scattering measurements at ambient temp. and temp. dependent small angle neutron scattering (SANS) expts. between 30 °C and 150 °C. DLS measurements at ambient temp. indicate a swelling of the formed structures with increasing amt. of EAN up to a certain threshold. The SANS expts. were performed below this threshold. The data evaluation of such concd. systems like microemulsions is possible with the "generalized indirect Fourier transformation" method (GIFT). We evaluated the small angle scattering data via the GIFT method, for comparison we also applied the model of Teubner and Strey (TS) which was often used to describe scattering curves of microemulsions. The GIFT method gives good fits throughout the exptl. path, while the TS model gives relatively poor fits. Both, light scattering and SANS results are in agreement with the existence of EAN droplets stabilized by surfactant with dodecane as continuous phase along the whole investigated temp. range. Moreover, these results clearly demonstrate the possibility to formulate high temp. stable microemulsions with ionic liqs. at ambient pressure.