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

Abstract

The influence of the perfluorinated fatty acid perfluorotetradecanoic acid (CF3(CF2)12COOH; 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.