Temperature‐Dependent Surface‐Enrichment Effects of Imidazolium‐Based Ionic Liquids

Abstract

We present the first systematic study of the influence of temperature on the degree of surface enrichment of 1-alkyl-3-methylimidazolium-based ionic liquids (ILs). Using angle-resolved X-ray photoelectron spectroscopy, we demonstrate that the degree of surface enrichment strongly decreases with increasing temperature for all the studied ILs. For ILs with the same cation, but different anions, [C8 C1 Im]Br, [C8 C1 Im][TfO] and [C8 C1 Im][Tf2 N], no significant differences of the temperature-induced partial loss of surface enrichment are found. Measurements for [C4 C1 Im][TfO], [C8 C1 Im][TfO] and [C18 C1 Im][TfO] indicate a small effect of the chain length. For [C18 C1 Im][TfO], a continuous decrease of alkyl surface enrichment is found with increasing temperature, with no abrupt changes at the phase-transition temperature from the smectic A to the isotropic phase, indicating that the surface enrichment is not affected by this phase transition.

Temperature‐Dependent Surface Enrichment Effects in Binary Mixtures of Fluorinated and Non‐Fluorinated Ionic Liquids

“…This behaviori ndicates an increasing surface enrichmento ft he butyl chain with decreasing temperature. Similar effects have been observed in literature [24] for [C 8 C 1 Im]X with X À = Br,[ TfO], [Tf 2 N] and [C n C 1 Im][TfO] (n = 4, 8, 18). We assign these effects to the increasei nm agnitude of the entropic term ÀTDS 0 with temperature, which favorsam ore random distribution of the constituents with increasing temperature.…”

Reactions of a Polyhalide Ionic Liquid with Copper, Silver, and Gold

“…A type K thermocouple was used to monitor the temperature of the heated samples, with a thermocouple controller to regulate the voltage of the heating filament. During measurements, the relative temperature was maintained to within ±0.1 °C; absolute sample temperature values were within ±5 °C …”

“…During measurements, the relative temperature was maintained to within AE 0.1 8C; absolute sample temperature values were within AE 5 8C. [27] In the XPS system, the radiation source was anon-monochromated Al Ka anode of aS pecs XR-50 dual-anode source, operated at 12 kV and a2 0mAe mission current. All spectra were recorded in normal emission to integrate over am aximum probing depth (7-9 nm, depending on the kinetic energy [20,28] )b yu sing aS cienta R3000 concentric hemispherical analyzer in constant pass energy mode with 200 eV pass energy for survey spectra and 100 eV for detailed spectra.…”

Growth of Multilayers of Ionic Liquids on Au(111) Investigated by Atomic Force Microscopy in Ultrahigh Vacuum

“…The properties of IL interfaces have been determined using various techniques. While the IL/vacuum interface has been investigated in detail using the methods of UHV-based surface science, ,,− the IL/solid interface underneath thick IL films has been mostly addressed at ambient conditions, by methods which sufficiently penetrate the IL film. These include reflection absorption infrared spectroscopy (RAIRS), sum-frequency generation, , X-ray or neutron reflectivity, , grazing incidence X-ray diffraction, and electrochemical methods. − The corresponding studies permit conclusions on the orientation of ions at and layering near the IL/solid interface.…”