SOLID MONOLAYERS ADSORBED AT THE SOLID-LIQUID INTERFACE STUDIED BY INCOHERENT ELASTIC NEUTRON-SCATTERING

Incoherent elastic neutron scattering has been used to demonstrate the presence of an immobile monolayer adsorbed at the interface between l iquid alkanes (methane, heptane, dodecane), an alkanol (dodecanol), an d a carboxylic acid (dodecanoic acid) and a graphite substrate. The de rived areas per molecule in the solid layers are consistent with the m olecules lying with their long axis parallel to the surface. Ia every case studied the layers were found to melt approximately 10% higher th an the melting points of the bulk materials. Diffraction data are used to confirm the two-dimensional nature of the solid monolayer in the c ase of methane. In every case there is also evidence for premelting of the bulk materials as the melting points are approached from below.