Molecular-Structure-Induced Under-Liquid Dual Superlyophobic Surfaces.

Surfaces with under-water superoleophobicity or under-oil superhydrophobicity have attractive features due to their widespread applications. However, it is difficult to achieve under-liquid dual superlyophobic surfaces, that is, under-oil superhydrophobicity and under-water superoleophobicity coexistence, due to the thermodynamic contradiction. Herein, we report an approach to obtain the under-liquid dual superlyophobic surface through conformational transitions of surface self-assembled molecules. Preferential exposure of either hydrophobic or hydrophilic moieties of the hydroxythiol (HS(CH2)nOH, where n is the number of methylene groups) self-assembled monolayers to the surrounding solvent (water or oil) can be used to manipulate macroscopic wettability. In water, the surfaces modified with different hydroxythiols exhibit under-water superoleophobicity because of the exposure of hydroxyl groups. In contrast, surface wettability to water is affected by molecular orientation in oil, and the surface transits from under-oil superhydrophilicity to superhydrophobicity when n ≥ 4. This surface design can amplify the molecular-level conformational transition to the change of macroscopic surface wettability. Furthermore, on-demand oil/water separation relying on the under-liquid dual superlyophobicity is successfully demonstrated. This work may be useful in developing the materials with opposite superwettability.

A universal fluorous technology toward superhydrophobic coatings.

HYPOTHESIS: Development of a process yielding large-sized non-wettable coatings of immediate applicative interest seems feasible by associating a membrane spining technique with the artificial mimic of a bio-inspired strategy toward water repellency. Accordingly, the question that arises is how to design a multiscale textured and chemically-activated continuous film. EXPERIMENTS: A novel synergic combination of a processing technique and chemical treatment was developed in this purpose. Fluorinated nanocarbons were included in polyvinylpyrrolidone (PVP) microfibers via their addition in a precursor solution for electrospinning. The nanocomposites thus obtained were subsequently treated under gaseous molecular fluorine in mild conditions. FINDINGS: Owing to the reactivity of PVP with F2, both etching and functionalization occurred during such a post-treatment. The chemical modification undergone by PVP upon fluorination has been analyzed and a mechanistic approach proposed. An impressive dual texturing developed at the micro- and nanoscale thanks to the combined action of electrospinning, polymer etching and emergence of the nanofillers. This allowed a stable with time superhydrophobic coating-like film to be achieved.