The structure of a multilayer of lead stearate

A study has been made of the molecular and crystallographic structures of Langmuir–Blodgett multilayer films of lead stearate. Electron microscopy and diffraction were used in the examination of such a film which had separated from the glass slide on which it had been formed. The films consist of a large number of three-dimensionally ordered lead stearate crystals arranged in near-perfect alignment, with the longest axes of their unit cell projecting from the plane of the supporting substrate. The unit cell of the lead stearate crystal is either monoclinic with the space group P2₁/a or orthorhombic with the space group P2₁2₁2. The former is considered to be rather the more likely. The major lattice spacings are 4.96 Å (100), 7.38 Å (010) and 47 Å (001). The β angle of the monoclinic unit cell is not known but is probably within a few degrees of 90°. The lead atoms are in special positions in the basal plane, regardless of which is the correct unit cell, and the hydrocarbon chains make an angle of 62±5 ° with the basal plane. Any free stearic acid in the films occurs as a separate phase.