Self-organization of semifluorinated alkanes and related compounds at interfaces: Thin films, surface domains and two-dimensional spherulites

Abstract

After a brief reminder of the specific properties of fluorocarbons, fluorinated chains and molecular fluorocarbonhydrocarbon diblocks (semifluorinated alkanes, CnF2n+1- CmH2m+1, FnHm) that account for their exceptional aptitude for self-organization, we review recent advances on the selfassembled surface nanodomains that FnHm diblocks form on water and solid surfaces, their shape and size characteristics, and their hierarchical organization into structures of higher complexity. Remarkably indeed, FnHm diblocks, when spread as Langmuir monolayers on water, self-assemble into circular mesoscopic nanodomains that exist even in the absence of lateral pressure, and self-organize into regular hexagonal arrays upon compression. These surface domains can be transferred essentially unchanged onto solid surfaces. They can also be obtained by direct casting or spin coating of solutions of diblocks on solids, or by spontaneous formation on liquid crystals. The nanodomains retain their size, shape and organization upon compression and, amazingly, even beyond the collapse of their Langmuir monolayers. The domain-patterned films display uncommon rheology, with predominantly elastic monolayers, and two-dimensional gels were generated, including at zero surface pressure. The formation and behavior of surface domains from related tri- and tetrablocks have also been reported. A tetrablock afforded the first example of pressure-driven stacking of self-assembled nano-objects. The domain-patterned films constitute attractive templates for organizing nanoparticles in components of electronic devices and sensors, and for fabricating ordered mesoporous solids. Most recently, a novel aggregation mode was found for FnHm diblocks, namely their crystallization into micron-size polycrystalline two-dimensional radial and/or ring-banded spherulites. Applications in medicine and materials science are being investigated.