Soft Matter Seminar: How salts can influence the structuredness of organic solvents: the curious case of glycerol carbonate
Pierandrea Lo Nostro, Department of Chemistry "Ugo Schiff", University of Florence, Italy
Glycerol carbonate (GC) is a dense, viscous, water soluble solvent (see left panel in Fig. 1). The high dielectric constant and dipole moment make it a suitable non-aqueous green solvent for several salts in different applications, e.g. in the technology of lithium-ion batteries, cement, sugar cane treatment, cosmetics and detergents [1-3]. Like other cyclic carbonates (ethylene and propylene carbonate), GC dissolves significant amounts of inorganic salts [4,5].
In this work we carried out solubility, conductivity, rheology, DSC, NMR and FTIR experiments on solutions of different potassium salts in glycerol carbonate. The results suggest that in the case of KF, the solvent becomes oversaturated and leads to the formation of a glassy liquid where GC molecules and KF ion pairs are intercalated in a rather ordered tridimensional structure, stabilized by cation-dipole interactions while the basic anion participates in hydrogen bonding , as depicted in the right panel of Fig. 1.
Figure 1. Left: chemical structure of glycerol carbonate. Black, red and white sphere represent carbon, oxygen and hydrogen atoms, respectively. Right: schematic structure of a KF oversaturated solution in glycerol carbonate. Purple and light blue spheres represent K+ and F- ions, respectively.
A similar behavior was observed in the presence of other basic (HB-acceptor) anions, such as carbonate, cyanate and phosphate. On the other hand, if the anion is not an HB-acceptor (as in the case of Cl-, Br- and NO3-), then its interaction with the solvent molecule is minimal. However, in the case of iodide, we recorded another peculiar behavior that is probably related to strong non-electrostatic interactions between I- and the GC ring as shown particularly by NMR, DSC (glass transition temperature), and FTIR results.
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Monday, July 16, 2018 at 2:00pm to 3:30pm
Reiss Science Building, 112
37th and O St., N.W., Washington