Determination of the Properties of Nanoconfined Ionic Liquids in Porous Silicon Oxide Matrices by NMR Techniques

FABIÁN VACA CHÁVEZ; CRISTIAN LÉPORI; HORACIO CORTI

Porto

Congreso; SMASH 2019 NMR Conference; 2019

Ionic liquids (ILs) are liquid salts formed by organic cations and organic or inorganic anions. They areused in replacement of traditional organic solvents as a reaction medium or in electrochemistry as aconductive solvent, among other applications [1]. But this liquid nature causes difficulties, such aspackaging, leakage and portability. For this reason, the study of the confinement of LIs within porousmatrices acquired great importance in recent times, since it maintains its liquid dynamics but with abehavior of solid material, such that in lithium batteries they function effectively as solid electrolytes [2].On the other hand, it is already known that the NMR technique is sensitive to order and molecular dynamics.In particular, measurements of spin-network (T1) and spin-spin (T2) relaxation times provide detailedinformation on intramolecular and/or intermolecular interactions and molecular reorientation movements[3]. The purpose of this work was to study the dynamic characteristics of the protic hydrophilic ILethylammonium (EAN) and of the aprotic hydrophobic IL 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (emimTFSI) confined in silicon oxide matrices with pores of the orderof nanometers, as well as molecular organization and fluid-pore interaction.Measurements of T1 and T2 were carried out as a function of temperature in a range between Tm and Tm +100 °C, where Tm is the IL melting temperature. In addition, the relaxation profiles of T1 were measured,that is, the dependence on the Larmor frequency of T1 (NMRD, its acronym in English). The systemsstudied were the ILs EAN and emimTFSI confined in porous matrices with pores between 3 nm and 60 nm.With these results it is possible to obtain information about molecular dynamics at different time scalesbetween 10-10 and 10-5 sec.It was observed that relaxation times change significantly reflecting the effect of confinement in both ILsdue to the interaction of these with the pore surface, regardless of the hydrophobicity characteristics of eachLI. This effect is more noticeable when the pore size is below 5 nm, which is reflected in the relaxationprofiles where the obtained curves reflect movements much slower than in bulk.