Understanding and controlling the molecular organization of amphiphilic molecules at interfaces is essential for materials and biological sciences. When spread on water, the model amphiphiles constituted by Cn,F 2n+1CmH2m+1 (FnHm) diblocks spontaneously self-assemble into surface hemimicelles. Therefore, compression of monolayers of FnHm diblocks is actually a compression of nanometric objects. Langmuir films of F8H16, FSH18, F8H20, and F1QH16 can actually be compressed far beyond the "collapse" of their monolayers at ∼30 Å2. For molecular areas A between 30 and 10 Å2, a partially reversible, 2D/ 3D transition occurs between a monolayer of surface micelles and a multilayer that coexist on a large plateau. For A < 10 Å2, surface pressure increases again, reaching up to ∼48mNm-1 before the film eventually collapses. Brewster angle microscopy and AFM indicate a several-fold increase in film thickness when scanning through the 2D/3D coexistence plateau. Compression beyond the plateau leads to a further increase in film thickness and, eventually, to film disruption. Reversibility was assessed by using compression-expansion cycles. AFM of F8H20 films shows that the initial monolayer of micelles is progressively covered by one (and eventually two) bilayers, which leads to a hitherto unknown organized composite arrangement. Compression of films of the more rigid F10H16 results in crystalline-like inflorescences. For both diblocks, a hexagonal array of surface micelles is consistently seen, even when the 3D structures eventually disrupt, which means that this monolayer persists throughout the compression experiments. Two examples of pressure-driven transformations of films of self-assembled objects are thus provided. These observations further illustrate the powerful self-assembling capacity of perfluoroalkyl chains.
- Fluorocarbon/hydrocarbon diblocks
- Langmuir-Blodgett films
ASJC Scopus subject areas
- Organic Chemistry