Intriguing transport dynamics of ethylammonium nitrate–acetonitrile binary mixtures arising from nano-inhomogeneity

Significance 

Transport features of fluid mixtures are critical to a number of industrial and biological applications. Having an in-depth understanding is therefore important to realize a complete characterization of a system. The mixing behavior of ionic liquids with neutral molecular solvents has drawn significant attention because the unique chemical and physical characteristics of these materials could result in enhanced alternatives to typical organic solvents.

The transport features of binary mixtures containing ionic liquids are quite interesting owing to the improved mobility of ions if a co-solvent is added to the system. It has been shown that water impurities from the atmosphere can significantly affect the transport characteristics of ionic liquids. Therefore, any experiments involving ionic liquids should be done in a controlled atmosphere.

Ethylammonium nitrate is a room temperature ionic liquid that has been widely analyzed as a pure compound and as a mixture with other ionic liquids and organic solvents. Acetonitrile on the other hand is a polar solvent that has been applied in organic chemistry for electrochemical applications. Binary mixtures of the two compounds have been studied on the conductivity of the Ethylammonium nitrate-acetonitrile mixture. It has been found that this system exhibits a nearly perfect behavior implying that acetonitrile just dilutes the ionic liquid therefore leaving it almost unaffected.

Binary mixtures of acetonitrile and Ethylammonium nitrate have unique features originating from their dynamical and structural nano-heterogeneity. These features are further pronounced when Ethylammonium nitrate is the minority component. In recent research collaboration between scientists at La Sapienza University of Rome and Rutgers University, researchers analyzed the transport characteristics conductivity, and self-diffusion of binary mixtures of acetonitrile and Ethylammonium nitrate. Their research work is published in journal Physical Chemistry Chemical Physics.

The authors found that a complex series of interactions govern the dynamics of the mixtures at macro- and micro-scale levels. Shear viscosity was one metric for the entire molecular mobility and indicated strong variation for this system. This behavior was attributed to the formation of large-scale aggregates that behaved similar to colloidal aggregates, therefore increasing the viscosity in the Ethylammonium nitrate-rich region.

The researchers observed that at the molecular-size level, the diffusion coefficients of acetonitrile and the cation had an inhomogeneity in the Ethylammonium nitrate-poor regime, indicating that the samples were far from being idealized.

In view of the mobility of the ionic liquid itself, the conductivity measures indicated strong ionic paring in the Ethylammonium nitrate-poor region. However, the specific structure adopted by the ionic liquid at these compositions, along with the lowered viscosity, was responsible for the improved conductive power of the mixtures.

In light of the findings, Ethylammonium nitrate-acetonitrile mixtures show a significant mesoscopic inhomogeneity that considerably affects the transport features of the system.

About the author

Lorenzo Gontrani received his degree from Rome “La Sapienza” university in 1998 in the group of Prof. R. Caminiti, with a thesis on quantum chemical calculations, liquid X-Ray diffraction and infrared spectroscopy. Then he received his PhD from Pisa university in 2002, where he worked in the theoretical chemistry group of Prof. J. Tomasi and B. Mennucci, where the famous Polarizable Continuum Model PCM was created and actively developed.

He is author of about 75 papers on major journals and currently works in the field of the molecular modeling simulations of Ionic Liquids and Deep Eutectic Solvents (DES), also coordinating mixed theoretical-computational research groups.

Reference

Alessandro Mariani, Matteo Bonomo, Boning Wu, Barbara Centrella, Danilo Dini, Edward W. Castner Jr. and Lorenzo Gontrani.  Intriguing transport dynamics of ethylammonium nitrate–acetonitrile binary mixtures arising from nano-inhomogeneity. Physical Chemistry Chemical Physics, volume 19 (2017), 27212.

Go To Physical Chemistry Chemical Physics

Check Also

Enhancing Mid-Infrared Er,Cr:YSGG Laser Pulse Performance via LiNbO₃ Acousto-Optic Q-Switching and Thermal Lensing Compensation - Advances in Engineering

Enhancing Mid-Infrared Er,Cr:YSGG Laser Pulse Performance via LiNbO₃ Acousto-Optic Q-Switching and Thermal Lensing Compensation