The structure of hexane/perfluorohexane thin liquid films

Thin films of the binary liquid mixture hexane/perfluorohexane were prepared on silicon wafers. The film thicknesses were between 140 Å and 350 Å; this range was chosen in order to achieve strong confinement of the mixture. The vertical structure of these films was investigated by means of x-ray reflectivity measurements. The data show that the component with the lower surface tension (perfluorohexane) segregates in the surface region of the films in agreement with theoretical predictions. Furthermore, no complete miscibility of the two components was observed in regions of the phase diagram where a one-component bulk system is expected. Preliminary results are given for the internal hexane/perfluorohexane interface.