Control of the geometry of the adsorbed thin layer by the depletion interaction.

The depletion interaction was reported to drive the mixtures of rodlike colloids and polymer coils into a variety of phase transitions such as isotropic-nematic, nematic-smectic, and so forth. We describe in this Communication a convenient preparation of the self-assembled monolayer of the platelike porphyrin molecules by the depletion interaction between the absorbent and the metal substrates. After the depletant, low molecular weight poly(ethylene oxide) (PEO), was added into the porphyrin/ethanol solution, random oriented porphyrin was then regulated to lie parallel to the adjacent metal substrates, forming the self-assembled monolayer.