Pattern Formation in a Substrate-Induced Phase Transition during Langmuir−Blodgett Transfer

An atomic force microscope study of Langmuir−Blodgett films deposited from the liquid expanded phase was undertaken to explore self-organizing methods of creating patterned surfaces. Although tetradecanoic (TDA), pentadecanoic (PDA), and hexadecanoic acid (HDA) monolayers deposited on silicon oxide at pH = 5.8 are uniform flat films, when the same monolayers are deposited on silicon oxide at pH = 9.3 or on mica substrates, the molecules organize into close-packed “islands”, indicative of a two-dimensional condensation. The substrate dependence of this islanding behavior suggests that surface charge plays an important role. Small islands have compact morphology, while large islands are dendritic. The length scale for the fingering instability changes by 2 orders of magnitude between TDA and HDA, from 60 nm to 6 μm.