Structural and compositional mapping of a phase-separated Langmuir-Blodgett monolayer by atomic force microscopy

COLL 203

Shatha E Qaqish, shatha.qaqish@usask.ca and Matthew F Paige, matthew.paige@usask.ca. Department of chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK S7N 5C9, Canada
A phase-segregated Langmuir-Blodgett (LB) film of arachidic acid (C19H39COOH) (AA) and perfluorotetradecanoic acid (C13F27COOH) (PA) was characterized by Atomic Force Microscopy (AFM). The LB film consists of a series of hexagonal, discontinuous domains dispersed in a continuous domain. Selective, in-situ dissolution of AA by n-hexadecane, followed by high-resolution topographical imaging indicate that the hexagons are primarily AA, whereas the surrounding area is a mixture of both AA and PA. In addition, the effects of variables such as the surface pressure and deposition temperature on the film's composition and morphology were studied. The structural changes of the monolayer were measured by AFM and confirmed by the selective in-situ dissolution in hexadecane. The results are described in terms of a simple kinetic model of phase separation.