Solvent effects on the monolayer structure of long n-alkane molecules adsorbed on graphite

Neutron diffraction patterns of dotriacontane (n-C32D66) monolayers adsorbed on an exfoliated graphite substrate from a heptane (n-C7D16) 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-C32D66 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.