Solvent Effects on the Monolayer Structure of Longn−AlkaneMolecules Adsorbed on Graphite

Neutron diffraction patterns of dotriacontane ( $n{-\mathrm{C}}_{32}{\mathrm{D}}_{66}$) monolayers adsorbed on an exfoliated graphite substrate from a heptane ( $n{-\mathrm{C}}_7{\mathrm{D}}_{16}$) solution reveal striking differences in the molecular orientation, lattice constant, and coherence length from those of the same monolayer adsorbed from the gas phase. Neither $n{-\mathrm{C}}_{32}{\mathrm{D}}_{66}$ monolayer phase appears to be fully consistent with Groszek's model of $n$-alkane registry on the graphite (0001) surface. A reversible transformation between the two monolayer phases can be induced by adding as little as a monolayer of the heptane solvent.