Pattern Formation in Phase-Separated Langmuir and Langmuir Monolayer Films

Abstract

Mixed monolayer films comprising hydrogenated and fluorinated surfactants can undergo phase separation to produce interfaces with diverse structures at the micrometer and nanometer scales. This review discusses our progress over the past decade to probe the relationship that exists between the molecular structure of the surfactants that comprise the films and the overall patterns formed in the monolayers. We review two main classes of mixed perfluorocarbon–hydrocarbon surfactant systems, including fatty acids and a recently developed family of EDTA-based gemini surfactants. In addition to summarizing the state-of-the-art of this field, the key scientific questions and relationships that require further elucidation are discussed, along with directions for continuing research into this fascinating area of research.

Mixing in Langmuir Monolayers: Perfluorotetradecanoic Acid and a Gemini Surfactant without a Linker

“…This effect has been exploited to control phase separation and resulting film structure in simple fatty acid systems and as the behavior of the C 18 -0-C 18 geminis appears to be similar to that of fatty acids, similar control is plausible. An additional question is why the unique polygonal domain structures that have been reported in other perfluorinated surfactant-containing monolayers (see 6,7,31 for example) are not present in the mixed gemini systems, despite the ability of both components to pack into crystalline films. This remains an elusive question and one that will be explored in more detail, and we posit that there are some subtle chemical structure requirements for the hydrogenated component in order to generate the polygonal domains.…”

“…Immiscibility is further refined by the molecular-level interactions between surfactants that are a function of the detailed chemical structure of the film constituents. This mutual immiscibility can lead to intriguing pattern formation in a variety of mixed films, and the subject matter has been reviewed extensively elsewhere. , Work in our group has focused on mixed systems containing simple perfluorinated fatty acids, primarily perfluorotetradecanoic acid [PF; CF 3 (CF 2 ) 12 CO 2 H, Scheme ].…”

“…This mutual immiscibility can lead to intriguing pattern formation in a variety of mixed films, and the subject matter has been reviewed extensively elsewhere. 6,7 Work in our group has focused on mixed systems containing simple perfluorinated fatty acids, primarily perfluorotetradecanoic acid [PF; CF 3 (CF 2 ) 12 CO 2 H, Scheme 1].…”

Effect of perfluorotetradecanoic acid on the morphology of a photopolymerizable phospholipid monolayer at the air‐water interface

“…Our group and others have been investigating the ability to pattern surfactants into micron‐scale structures in monolayer films by mixing mutually immiscible hydrogenated and perfluorinated surfactants; progress in this field has been recently reviewed (Paige & Eftaiha, 2017; Yan & Paige, 2021). In this approach to surface patterning, binary mixed monolayers comprised of a hydrogenated and a fluorinated surfactant form well‐defined, phase‐separated domains, with domain morphology depending strongly upon the precise chemical structure of the constituent surfactants.…”

Interfacial Behavior of Giant Amphiphiles Composed of Azobenzene and Polyhedral Oligomeric Silsesquioxane

“…A Langmuir monolayer on a water surface is an excellent model system for studying ordering in 2D. Langmuir films of amphiphilic molecules, such as small-molecule surfactants, lipids, and block copolymers, have been studied for many years. − Owing to its tunable photoresponsive properties, the azobenzene unit has been incorporated into amphiphilic molecule systems to fabricate various functional thin films. − …”