Structure and Polarity of the Phase Boundary of N-Methylimidazolium Chloride/Silica

The adsorption of N -methylimidazolium chloride ([Hmim]Cl) on Aerosil300 from dichloromethane solution has been studied by measuring the UV/vis absorption spectra of co-adsorbed solvatochromic probes. Additionally, solid state 29 Si-{ 1 H}-CP-MAS, 1 H-HR-MAS NMR, and DRIFT spectroscopy studies show that physisorption of [Hmim]Cl on Aerosil300 takes place. Fe(phen) 2 (CN) 2 ( 1 ), 3-(4-amino-3-methylphenyl)-7-phenyl-benzo-[1,2-b:4,5b′]-difuran-2,6-dione ( 2 ), and 4- tert -butyl-2-(dicyanomethylene)-5-[4-(diethylamino)benylidene]-Δ 3 -thiazoline ( 3 ) were used as solvatochromic surface polarity probes. The UV/vis absorption spectra of the probes 1, 2, and 3 co-adsorbed on the adsorbates were measured as function of the surface loading with [Hmim]Cl in reflection technique. The Kamlet−Taft’s α (hydrogen bond donating ability), β (hydrogen bond accepting ability), and π* (dipolarity/polarizability), respectively, parameters of the [Hmim]Cl/Aerosil300 phase boundary have been calculated using the linear functions of υ max (probe) with the solvent parameter of solvents, which serve as the reference system. The α value of Aerosil300 significantly decreases with an increasing amount of adsorbed [Hmim]Cl. β values are specified by the adsorbed chloride ion. Increasing salt loading of the solid surface increases β. The calculated β values range between those of pure Aerosil300 and [Hmim]Cl. The dipolarity/polarizability of the [Hmim]Cl-loaded silica particles goes through a maximum as a function of the loading and decreases below the value of pure Aerosil300 and [Hmim]Cl. This result is a clear indication for a lowering of the anion−cation interaction of [Hmim]Cl due to the physisorption onto the surface silanol groups.