The effect of perfluorotetradecanoic acid on the structure of photopolymerized 10,12-pentacosadiynoic acid films at the air-water interface

The influence of the perfluorinated fatty acid perfluorotetradecanoic acid (CF3(CF2)(12)COOH; PF) on the structure of films of the photopolymerizable surfactant 10,12-pentacosadiynoic acid (PCDA) has been explored at the air-water interface through a combination of surface pressure-area compression measurements and Brewster angle microscopy imaging during the time course of UV photopolymerization. The addition of the perfluorocarbon to PCDA results in a film structure that differs significantly from the pure PCDA alone, with the most pronounced difference being the formation of photopolymer strands oriented perpendicular to the direction of film compression in a Langmuir trough. Film compression data, supported by in situ fluorescence spectrophotometry and atomic force microscope images of deposited films, suggest that compression-induced stress and accompanying film buckling, enhanced by the strong cohesion between PF and PCDA, contributes to the observed structural differences between the mixed PF-PCDA and pure PCDA photopolymerized films. This approach to forming patterned polydiacetylene films is discussed in comparison with other demonstrated methods for structuring this technologically important polymer.