Bis-polyethylene glycol-functionalized imidazolium ionic liquids: A multi-method approach towards bulk and surface properties

Combined Surface Light Scattering and Pendant-Drop Experiments for the Determination of Viscosity and Surface Tension of High-Viscosity Fluids Demonstrated for Ionic Liquids

“…The chemical structures of the two studied imidazolium-based ILs 1-methyl- ] purchased from Iolitec showed a weak yellowish color, [(mPEG 2 ) 2 Im]I was self-synthesized according to a procedure described in literature [19] and features an intense yellow to brown color. In addition, the four colorless reference liquids, namely, n-dodecane (n-C 12 H 26 ) and toluene provided by Merck KGaA, tris(2-ethylhexyl) trimellitate (TOTM) purchased from Sigma-Aldrich, and deionized water (H 2 O) obtained from a Milli-Q system, were investigated by PD measurements and, in case of n-C 12 H 26 and TOTM, additionally by SLS since they allow to cover a broad range of surface tensions and dynamic viscosities.…”

“…5 and 6, a check of the hydrodynamic theory in connection with the SLS experiments is carried out for both ILs at selected T. Figure 8 depicts the q-dependency of the measured values for Γ for the recorded overdamped signals applying the R-P and R-NP configurations, in comparison with theoretical dampings calculated from the hydrodynamic theory. For these, input quantities for η L and σ are taken from the present CV and PD measurements in the case of [OMIM][PF6] as well as from the work of Seidl et al [19] in the case of [(mPEG 2 ) 2 Im]I. As can be observed from Fig.…”

“…The surface tensions for [(mPEG 2 ) 2 Im]I are larger than those for [OMIM][PF 6 ], with a relatively constant deviation about + 36 % for the entire T range studied. Considering the fact that only the outer region at the surface is responsible for surface tension according to Langmuir's principle [43], the behavior for σ can be discussed in connection with the enrichment of the most surface-active groups of the two ILs, as revealed by angle-resolved X-ray photoelectron spectroscopy [15,19]. While for [(mPEG 2 ) 2 Im]I the surface shows a weak enrichment of the short-chained (n = 2) polar mPEG n side chains, the surface of [OMIM][PF 6 ] is predominantly occupied by the long-chained non-polar octyl side chains of distinctly lower surface energy, resulting in a significantly lower value for σ.…”

“…Here, the analysis of σ is based on the comparison between the recorded shape of an axisymmetric PD and its theoretical description by the Young-Laplace equation [13]. In our previous studies [14,18,19], the PD method was used to determine σ for ILs and IL mixtures as a function of temperature with typical expanded uncertainties (coverage factor k = 2) of 2 %. An alternative to conventional methods is surface light scattering (SLS).…”

Combined Surface Light Scattering and Pendant-Drop Experiments for the Determination of Viscosity and Surface Tension of High-Viscosity Fluids Demonstrated for Ionic Liquids

“…Here, also a comparison with own viscosity results from capillary viscometry and available experimental data in the literature is carried out. [OMIM][PF 6 ] purchased from Iolitec showed a weak yellowish color, [(mPEG 2 ) 2 ]I was self-synthesized according to a literature procedure [19] and features an intense yellow to brown color. In addition, the four colorless reference liquids, namely, n-dodecane (n-C 12 H 26 ) and toluene provided by Merck KGaA, tris(2ethylhexyl) trimellitate (TOTM) purchased from Sigma-Aldrich, and deionized water (H 2 O) obtained from a Milli-Q system, were investigated by PD measurements and, in case of n-C 12 H 26 and TOTM, additionally by SLS since they allow to cover a broad range of surface tensions and dynamic viscosities.…”