Phase transition in the molecular crystal structure of Langmuir-Blodgett film containing pyrrole: Molecular mechanics simulations

We studied, by atomic force microscopy (AFM), the changes in the molecular arrangement of arachidic acid (C₂₀) Langmuir-Blodgett (LB) film with increasing quantity of pyrrole (Py) molecules which we used as spacer molecules for C₂₀ molecules in the LB film. When the concentration of Py molecules in the C₂₀ LB film was increased from 0% to 150%, the crystal structure of the LB film changed as follows: oblique lattice→hexagonal lattice→square lattice. These observations agreed qualitatively with the results of computer simulation based on molecular mechanics. Precise control of the crystal structure of LB film by adjusting the number of spacer molecules such as Py in the LB film is possible.