Surface segregation of a binary liquid mixture as studied by metastable impact electron spectroscopy

Abstract

We have investigated the free liquid surface of a binary mixture of formamide and benzylalcohol using MIES (= metastable impact electron spectroscopy) and UPS. Whereas the latter samples information down to a depth of ~ 6A the method MIES is sensitive exclusively for the topmost molecular layer. The combination of both techniques allows us to determine the parameters of an exponential segregation profile. As expected from its smaller surface tension benzylalcohol is strongly enriched at the surface. The segregation depth is greatest (~ 12 A) at small molar fractions of benzylalcohol. Once the segregation profile is established it is straightforward to compute the surface excess. We find very good agreement with the prediction of the Gibbs equation.

The static and dynamic surface composition of formamide-benzyl alcohol and water-formamide liquid mixtures studied by means of HeI photoelectron spectroscopy

“…The relative contribution to the mixture spectrum is always found to be higher than the value for the bulk composition, reaching a maximum of six times the bulk value near 10 vol % benzyl alcohol. This result is identical to the reported data of Morgner et al [13].…”

“…It should be noted that there is no smooth variation of the overall position of the component spectra as a function of the bulk molar fraction, contrasting with the observations of the core level ionization bands reported by Siegbahn et al [9]. This was stated before by Morgner et al [13]for UPS and MIES measurements and is con® rmed by our experimental data.…”

“…The same vapour pressure limitations as above are valid for the recent successful investigations in the group of Morgner [13], where a combination of UPS and electron detection after metastable helium deexcitation He* (MIES) at liquid surfaces was developed to obtain detailed information about the surfaces of binary liquid mixtures, e.g., of formamide± benzyl alcohol. There the di erence between the He* ionization localized on top of the surface and the UPS ionization, where a related electron escape depth of 6 A Ê is assumed, gives information about two molecular monolayers at the surface.…”

“…The same mixture was studied using a combination of UPS and MIES by Morgner et al [13]. The spectrum stripping routine was used in this investigation to evaluate the surface fraction of the components, and a comparison of the results with the predictions of the Gibbs equation was discussed.…”

The first stages of lipid layer formation. A metastable impact electron spectroscopy study of egg lecithin dissolved in hydroxypropionitrile

“…In previous studies on polar solvents, binary mixtures and salt solutions [6][7][8][9] we have never encountered an effect of this voltage on our spectra, apart from a smooth change of relative intensity as a function of electron energy. However, a recent study on a phospholipid monotayer [10] demonstrated the effect of an inhomogeneous electric field on the motion of lipid molecules within the surface layer on a time scale of the order of several seconds.…”