Neutron reflection has been applied to probe the nature and extent of adsorption from a mixture of (1-x)n-hexane+x perfluoro-n-hexane against silicon substrates modified with alkylsilane (fluorophobic) or fluoroalkylsilane (fluorophilic) coupled layers. For an equimolar mixture (x=0.5, 60.7 vol %) in the one-phase region at T=30 degreesC-removed both in temperature and composition from the upper critical point at 22.65 degreesC and x=0.36-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 similar to20 Angstrom and composed of similar to83 vol % n-hexane, and the second, more dilute layer has a composition profile which decays smoothly into the bulk over a range of similar to100 Angstrom. A similar result is found for the fluorophilic surface, but in this case the layer closest to the substrate is similar to15 Angstrom thick and composed of similar to95 vol % perfluoro-n-hexane. Qualitatively similar behavior is found for adsorption from a mixture with x=0.7 against a fluorophobic substrate and for a mixture with x=0.2 against a fluorophilic substrate. (C) 2003 American Institute of Physics.