Surface structures of binary mixture of ionic liquids

Determining the composition of the vacuum–liquid interface in ionic-liquid mixtures

“…where Ai is here the molar surface area of component i, n = A1/A2, and x2 s can be obtained simply from x1 s + x2 s = 1. Although, as noted by Nakajima et al, 29 the prediction is not too far from their observed HRBS result at x = 0.5, the qualitative behaviour over the full range of x measured in our RAS-LIF experiments is very poorly reproduced by eqn (4). The level of agreement is again not materially changed by modest differences in the surface tension values reported here and elsewhere.…”

“…These areas could be estimated simply from bulk densities with an assumption of cubic geometry, or ostensibly more accurately from the observed areal atomic densities in their HRBS experiments. 15 U N -area estimates 29 and our own measured surface tensions for [C2mim](1-x)[C12mim]x[NTf2] mixtures above, the dependence of surface mole fraction on bulk mole fraction shown in Fig. 6 is predicted, where it is compared with our RAS-LIF measurements of surface exposure.…”

“…This can be challenging to define or estimate accurately, beyond some simplistic assumption of an approximately cubic (or, within a scaling factor, spherical) geometry; otherwise, an independent direct measure of the areal density is needed. 15,29 We have shown previously that choosing either the area or the volume does not alter the qualitative form of the behaviour in plots such as those in Figure 5. 27 In what follows, we use these different independent variables appropriate to the basis on which the various expressions we will introduce have been developed.…”

“…29 The observed surface mole fraction of [C12mim][NTf2] was reported to be 0.66 ± 0.06. We have indicated this point in Fig.…”

“…These are attractive for potential applications because the properties can be fine-tuned by simply varying the mixing ratio, rather than having to synthesize a large number of chemically distinct compounds. Their surface properties have begun to be examined by direct techniques, 13,15,[27][28][29][30] but the data remain relatively sparse. In particular, there have been no systematic attempts to investigate the relationships between these direct measures and the more-established but indirect measurement of surface tensions.…”