Effect of Lithium Salt on the Stability of Dispersions of Fumed Silica in the Ionic Liquid BMImBF4

摘要

We have investigated the stability and interactions in dispersionsnof colloidal fumed silica, Aerosil 200, and the ionic liquid 1-butyl-3-nmethylimidazolium tetraflouroborate (BMImBF4) as a function of the Li saltnconcentration (LiBF4). Photon correlation spectroscopy was used to study thenaggregation behavior at low silica concentrations, and Raman spectroscopy wasnused to investigate the interactions in the ionic liquid and with the silica surface.nWe find that the addition of LiBF4 increases the stability of the dispersions,nwith smaller agglomerates of silica particles and higher gelation concentrationsnin the presence of Li salt. The increased stability with the addition of Li salt isnexplained by the formation of a more stable solvation layer, where Li ionsnaccumulate on the surface. This leads to an increased interaction betweennlithium ions and the BF4n− anions in the solvation layer, as seen by Ramannspectroscopy. Upon gelation, the Li ions are expelled from the surface becausenhydrogen bonding between the silica particles are formed. For both neat BMImBF4 and Li-salt-doped BMImBF4/silicandispersions, a weak gel phase was found preceding the formation of a strong gel at slightly higher silica concentrations.