Thierry Darmanin

Recent advances in designing superhydrophobic surfaces.

The interest in superhydrophobic surfaces has grown exponentially over recent decades. Since the lotus leaf dual hierarchical structure was discovered, researchers have investigated the foundations of self-cleaning behavior. Generally, surface micro/nanostructuring combined with low surface energy of materials leads to extreme anti-wetting properties. The great number of papers on this subject attests the efforts of scientists in mimicking nature to generate superhydrophobicity. Besides the thirst for knowledge, scientists have been driven by the many possible industrial applications of superhydrophobic materials in several fields. Many methods and techniques have been developed to fabricate superhydrophobic surfaces, and the aim of this paper is to review the recent progresses in preparing manmade superhydrophobic surfaces.

Recent advances in the potential applications of bioinspired superhydrophobic materials

This review gives an overview of recent advances in the potential applications of superhydrophobic materials. Such properties are characterized by extremely high water contact angles and various adhesion properties. The conception of superhydrophobic materials has been possible by studying and mimicking natural surfaces. Now, various applications have emerged such as anti-icing, anti-corrosion and anti-bacterial coatings, microfluidic devices, textiles, oil–water separation, water desalination/purification, optical devices, sensors, batteries and catalysts. At least two parameters were found to be very important for many applications: the presence of air on superhydrophobic materials with self-cleaning properties (Cassie–Baxter state) and the robustness of the superhydrophobic properties (stability of the Cassie–Baxter state). This review will allow researchers to envisage new ideas and industrialists to advance in the commercialization of these materials.

Superhydrophobic Surfaces by Electrochemical Processes

This review is an exhaustive representation of the electrochemical processes reported in the literature to produce superhydrophobic surfaces. Due to the intensive demand in the elaboration of superhydrophobic materials using low-cost, reproducible and fast methods, the use of strategies based on electrochemical processes have exponentially grown these last five years. These strategies are separated in two parts: the oxidation processes, such as oxidation of metals in solution, the anodization of metals or the electrodeposition of conducting polymers, and the reduction processed such as the electrodeposition of metals or the galvanic deposition. One of the main advantages of the electrochemical processes is the relative easiness to produce various surface morphologies and a precise control of the structures at a micro- or a nanoscale.

Glycerol carbonate as a versatile building block for tomorrow: synthesis, reactivity, properties and applications

The synthesis, reactivity and applications of glycerol carbonate (glycerine carbonate or 4-hydroxymethyl-2-oxo-1,3-dioxolane) are discussed and reviewed. Supported by the increasing sustainable awareness, glycerol carbonate has gained much interest over the last 20 years because of its versatile reactivity and as a way to valorize waste glycerol. Numerous synthesis pathways for this molecule were identified, some of them very promising and on the verge of being applied at an industrial scale. The wide reactivity of this molecule due to the presence of both a hydroxyl group and a 2-oxo-1,3-dioxolane group has been studied and has initiated some emerging applications in various domains from solvents to polymers.

Molecular Design of Conductive Polymers To Modulate Superoleophobic Properties

Natural surfaces can be superhydrophobic, but on the other hand, superoleophobic properties are extremely rare. We demonstrate that modification of the 3,4-alkylenedioxy bridge length in pyrrole-derivative monomers can have a dramatic influence on the superoleophobic properties of electrodeposited conductive polymers. Here we report the synthesis and characterization of novel fluorinated 3,4-ethylenedioxypyrrole (EDOP) and 3,4-propylenedioxypyrrole (ProDOP) monomers and their corresponding electrodeposited polymers. The polymer surfaces were characterized by static and dynamic contact angle measurements, scanning electron microscopy, and cyclic voltammetry. Surprisingly, the antiwetting properties do not depend of the fluorocarbon chain length (F-octyl to F-hexyl) but are in fact governed by the nature of the electrochemically deposited core. Indeed, superhydrophobic and superoleophobic surfaces with extremely low hysteresis and sliding angles for water droplets were obtained by electrochemical polymerization of highly fluorinated EDOP, whereas highly fluorinated ProDOP gave only superhydrophobic surfaces with a sticky behavior. The difference in wettability is attributed to surface nanoporosity resulting from the doping process.

Superhydrophobic Fiber Mats by Electrodeposition of Fluorinated Poly(3,4-ethyleneoxythiathiophene)

The control of surface morphology and wettability is crucial in the development of superhydrophobic surfaces, which implies new strategy and molecular design. In this Article, we report the synthesis, characterization, and electrochemical properties of original 3,4-ethyleneoxythiathiophenes (EOTT) as platform molecules and its derivatives bearing a semifluorinated chain of various length (F-octyl, F-hexyl, F-butyl, and F-ethyl). We report the influence of the fluorinated chain length as well as the presence of sulfur atoms in the monomer on the surface construction and nonwetting properties of the corresponding electrodeposited polymer films. Surprisingly, these films exhibit the possibility to obtain extremely long polymer fibers with a possible control of their length by a careful choice in the monomer structure. We show that the presence of sulfur atoms in the monomer structure seems to be necessary to modulate the formation of extremely long polymer fibers by aggregation of smaller polymer fibrils. In this Article, the formation of superhydrophobic material (contact angle above 150°) for four, six, and eight fluoromethylene units but also highly hydrophobic surfaces (contact angle above 125°) from extremely short chains (two fluoromethylene units) is also demonstrated.

Superoleophobic behavior of fluorinated conductive polymer films combining electropolymerization and lithography

The surface construction to reach super oil non-wetting properties is very complex because of the necessary force for impeding the natural spreading of low surface tension oils. Here, a polymer, which is able to reach the superoleophobicity when it is electrodeposited on smooth surfaces, has been deposited on micro-patterned substrates made of cylindrical arrays (∅: 13 µm, H: 25 µm, distance between cylinders: 40 µm) in order to determine the effect of the pattern on the super oil-repellency properties. The surface analysis using various oils has shown that the pattern used highly decreases the time of deposition and, as a consequence, the required amount of polymer to obtain anti-oil surfaces. This work is the first step in the short term prospects for the elaboration of superoleophobic surfaces combining electropolymerization with lithography.

Surface Structuration (Micro and/or Nano) Governed by the Fluorinated Tail Lengths toward Superoleophobic Surfaces

As compared to superhydrophobic surfaces, the challenge to obtain superoleophobic properties, surfaces against low-surface-tension probe liquids such as hexadecane, is very important because of their high tendency to wet. From the molecular design of the monomer, it is possible to obtain in one step superoleophobic surfaces by electrodeposition. Hence, we report the synthesis and the characterization of an original series of fluorinated 3,4-ethylenedioxypyrrole (EDOP) derivatives. The electrodeposited polymer films are characterized by contact angle measurements (static and dynamic with various probe liquids), optical profilometry, and scanning electron microscopy. In the view toward reaching superoleophobic properties, a common approach is to increase the number of fluoromethylene units of the surface post-treatment agent. Here, surprisingly, it is possible, in one step, to reach more efficient antioil surface properties by decreasing the length of the fluorinated tail (F-octyl to F-hexyl). This fact can be explained by a double scale of structuration (micro and nano) induced using only F-hexyl tails.

Superoleophobic surfaces with short fluorinated chains

Due to the extremely low surface tension of oils, the elaboration of superoleophobic surfaces implies the development of well-defined strategies to impede their tendency to spread. Usually, these strategies combine the presence of re-entrant structures (overhang, mushroom-like, T-like structures, etc.) with perfluorinated compounds containing long perfluorinated tails. Due to the toxicity (bioaccumulative potential) of long perfluorinated tails, our strategy is to develop superoleophobic properties with short perfluorinated tails (perfluorobutyl or F-butyl). However, almost all our strategies failed because of their much lower intrinsic oleophobicity. Here, we show the possibility to reach superoleophobic properties by electrodeposition of original fluorinated (F-butyl, F-hexyl and F-octyl) 3,4-ethylenedioxythiophene derivatives containing an amide connector. Surprisingly, if superhydrophobic properties are obtained whatever the fluorinated chain length, superoleophobic properties are only obtained with F-butyl tails (θsunflower oil = 150.0° and θhexadecane = 132.1°). Here, the fibers, only obtained with F-butyl chains, have a much higher tendency to repel oils than spherical particles. It seems that the presence of nanofibrils (re-entrant structures) and amide connectors allow the stabilization of the Cassie–Baxter state (fakir state) to be increased with oil droplets, which makes it possible to reach a state close to the Cassie–Baxter state with a polymer containing F-butyl tails. We think that the amide connectors increase the presence of the F-butyl tails at the extreme surface by reducing their mobility.

Superhydrophobic Fibrous Polymers

Superhydrophobicity coming from the appropriate structuration, morphology, and low surface energy material, is a more and more demanded property in many fields. Especially superhydrophobic fibers are interesting because of their re-entrant structure and their potential applications in apparel. On the other hand, polymeric materials are of interest because of their versatility and their easy-to-implement. The complementarity of polymer and fiber morphology is interesting to develop. This review discuss on the various techniques to produce superhydrophobic fibrous polymer films.