SURFACE-MORPHOLOGY AND STABILITY OF LANGMUIR-BLODGETT MONOLAYERS AND MULTILAYERS OF SATURATED FATTY-ACIDS BY SCANNING FORCE MICROSCOPY

The molecular architecture of Langmuir-Blodgett (LB) films of saturated fatty acids of different lengths transferred onto flat solid supports (mica, SiO, highly oriented pyrolytic graphite) was investigated with the scanning force microscope (SFM) under ambient conditions. Intrinsic defects in the LB monolayer have been used to measure the film thickness, which changes by an apparent increment of 0.2 nm per methylene group. The influence of different solid supports on monolayer morphology was determined. The investigations were extended to three-dimensional superstructures by deposition of successive monolayers. Reorganization of the bilayer in contact with the aqueous subphase forms regions with different thickness. Molecular resolution was achieved with the SFM on films with more than two layers. We have also determined unit cell parameters of the LB film surface of different fatty acid multilayers. The lattice constants did not change significantly, but the amplitude of the surface corrugations increases with the length of the aliphatic chain. Energetic contributions to monolayer stiffness are discussed.