Structures of head-group and tail-group monolayers in a Langmuir-Blodgett film

We have studied monolayer and multilayer Langmuir-Blodgett films of lead stearate using x-ray diffraction and reflectivity. We show that it is possible to distinguish the scattering due to the head groups from that due to the alkane chains. The second and subsequent alkane monolayers are distorted hexagonal (the first monolayer is known to be hexagonal); successive monolayers are shifted laterally by one-fourth of an in-plane lattice spacing, and the chains tilt by ∼8° towards a nearest neighbor. The lead ion monolayers are also distorted hexagonal; successive monolayers are shifted laterally by a half lattice spacing. From rod scan intensities, we have determined the relative positions of the lead and alkane chain lattices.