Surface architectural changes upon sonication revealed with sum frequency generation spectroscopy of perfluoroalkyl carboxylic acids

Understanding the interfacial behavior of molecular films is essential for elucidating key processes in both environmental and industrial systems. In this study, we investigate the interfacial behavior of perfluorotetradecanoic acid using vibrational sum frequency generation (SFG) spectroscopy to directly compare its behavior in different monolayer architectures, i.e., a traditional Langmuir monolayer and a monolayer formed from a sonicated bulk solution. Our results reveal significant differences in the vibrational SFG spectra of the carboxylic acid head group between the two monolayer types. These findings demonstrate that monolayer type can fundamentally alter the interfacial structure of perfluoroalkyl carboxylic acids and highlight the importance of monolayer architecture in interpreting interfacial spectroscopic data.