Molecular order in Langmuir–Blodgett assembled films of an azobenzene amphiphile

Alternating multilayers of amphiphile, 4-{4-[Methyl-(4-octadecylcarbamoyl-butyl)-amino]-phenylazo}-benzenesulfonic acid (S-azo-C18), and stearic acid were deposited on hydrophobized silica surfaces using the Langmuir–Blodgett technique. Ellipsometry, UV–visible spectroscopy, and second harmonic generation were used to characterize the films, demonstrating reproducible deposition and suggesting a well ordered film structure. Despite the appearance of order at the macroscopic level, neutron and X-ray scattering results unequivocally show that there is considerable disorder, with significant interpenetration between the stearic acid and S-azo-C18 layers. These results suggest that molecular disorder in Langmuir–Blodgett deposited multilayer films may often go unrecognized mainly because the macroscopic probes based on these optical measurements are not adequate for determining the molecular level structural order.