Nanoscale Spatial Heterogeneity in Electrolyte-based Deep Eutectic Solvents: Temperature Dependent Behaviour
Supreet Kaur and Hemant K. Kashyap
Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi
Deep eutectic solvents (DESs) are recently emerged popular class of ionic liquids and are found to be very viable and environmentally benign alternative solvents. In the past decade these designer solvents have been used in various applications such as synthesis, catalysis, biotransformation, electrodeposition and many more. Knowing the full potential of these solvents and harnessing them in various domains requires the microscopic understanding of molecular level structure of these solvents. In this spirit, herein we present an all atom molecular dynamics investigation on the temperature dependence of structural organization in (alkylamide + electrolyte)-based DESs. The existence of unique nanoscale spatial organization in (alkylamide + Li+/ClO4-)-based DESs on molecular length scales has been previously revealed. It has been found that this heterogeneity is primarily due to the ion pair self segregation. This self segregation due to formation of Li+/ClO4- domains tends to increase with increase in temperature and also tail length of the alkylamide species. The marker of this heterogeneity is the so-called prepeak observed in both the X-ray and neutron scattering structure functions. We observe that the intensity of this prepeak tend to enhance with increasing temperature. We found that the increase in the heterogeneity is because of the enhanced correlations between the ionic species at higher temperature. Further partitioning of X-ray scattering structure functions reveal that rate of enhancement in the ionic correlations with temperature is more than the rate of diminution in the electrolyte alkylamide cross-correlations which leads to overall rise in the prepeak intensity with increasing temperature. The alkylamide alkylamide correlations are largely unaffected by any change in the temperature. Real space correlations and hydrogen bonding analysis also corroborate with these observations.
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