High molecular orientation in mono- and trilayer polydiacetylene films imaged by atomic force microscopy

Atomically flat monolayer and trilayer films of polydiacetylenes have been prepared on mica and silicon using a horizontal deposition technique from a pure wafer subphase. Langmuir films of 10,12-pentacosadiynoic acid (I) and N-(2-ethanol)-10,12-pentacosadiynamide (II) were compressed to 20 mN/m and subsequently polymerized by UV irradiation at the air-water interface. Blu e and red forms of the films were prepared by varying exposure times and in cident power. Polymerization to the blue-phase films produced slight contra ctions of 2 and 5% for the films of II and I, respectively. Longer UV expos ures yielded red-phase films with dramatic film contraction of 15 and 32% f or II and I, respectively. The horizontal deposition technique provided tra nsfer ratios of unity with minimal film stress or structure modification. A tomic force microscopy images revealed nearly complete coverage of the subs trate with atomically flat films. Crystalline domains of up to 100 micromet ers of highly oriented polydiacetylene molecules were observed. The results reported herein provide insight into the roles of molecular packing and ch ain orientations in converting the monomeric film to the polymerized blue a nd red phases. (C) 2000 Academic Press.