Adsorption from alkane+perfluoroalkane mixtures at fluorophobic and fluorophilic surfaces. I. Nature of the noncritical adsorption profiles

Abstract

Local structure of a phase-separating binary mixture in a mesoporous glass matrix studied by small-angle neutron scattering Adsorption from alkane+perfluoroalkane mixtures at fluorophobic and fluorophilic surfaces. II. Crossover from critical adsorption to complete wetting Neutron reflection has been applied to probe the nature and extent of adsorption from a mixture of (1Ϫx)n-hexaneϩx perfluoro-n-hexane against silicon substrates modified with alkylsilane ͑fluorophobic͒ or fluoroalkylsilane ͑fluorophilic͒ coupled layers. For an equimolar mixture (x ϭ0.5, 60.7 vol %͒ in the one-phase region at Tϭ30°C-removed both in temperature and composition from the upper critical point at 22.65°C and xϭ0.36-the structure was resolved at both fluorophobic and fluorophilic surfaces. Liquid mixtures with three different refractive index contrasts were used to reduce model ambiguity in the ensuing analysis. For both surfaces the composition profiles of the adsorbed liquids could be represented using two-layer slab models which included interlayer Gaussian roughness. For the fluorophobic surface, the thickness of the layer closest to the substrate is ϳ20 Å and composed of ϳ83 vol % n-hexane, and the second, more dilute layer has a composition profile which decays smoothly into the bulk over a range of ϳ100 Å. A similar result is found for the fluorophilic surface, but in this case the layer closest to the substrate is ϳ15 Å thick and composed of ϳ95 vol % perfluoro-n-hexane. Qualitatively similar behavior is found for adsorption from a mixture with xϭ0.7 against a fluorophobic substrate and for a mixture with xϭ0.2 against a fluorophilic substrate.

Preferential adsorption of solid monolayers of hydrocarbons over fluorocarbons at the solid/liquid interface

“…Perfluorohexane was preferentially adsorbed at the liquid-vapour interface with hexane preferentially adsorbed at the substrate. The results of the neutron reflectivity studies of Bowers et al [14] are also in general agreement with these findings.…”

Adsorption at the liquid-vapor surface of a binary liquid mixture

“…The critical region only forms FIG. A number of earlier reports have experimentally studied the adsorption behavior as a function of composition and temperature at the liquid-vapor surface of binary mixtures [14][15][16] and qualitatively attempted to explain the observations. ͑a͒ Schematic plot of the coexistence curve for an AB binary liquid mixture where component B possesses the lower surface tension and higher density compared with component A.…”

Structural Studies of Aliphatic Substituted Phthalocyanine−Lipid Multilayers

“…5 These novel and The focus of our project was to study the structure and hence hydrophobic layer on the silica surface. 9 In our previous work, we 84 have characterized this layer by measuring the reflectivity from the 85 Si-water interface using a series of contrasts. 9 …”

“…9 In our previous work, we 84 have characterized this layer by measuring the reflectivity from the 85 Si-water interface using a series of contrasts. 9 …”

“…9 The silicon oxide layer 174 and the C-18 hydrophobe layer were also characterized using the Table 1 T1 .…”