Sonia Amigoni

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.

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.

Covalent Layer-by-Layer Assembled Superhydrophobic Organic−Inorganic Hybrid Films

Using the concept of covalent layer-by-layer assembly (covalent LbL), used until now for the elaboration of films from polymers or dendrimers, we have constructed hybrid organic/inorganic surfaces by alternating different layers of amino-functionalized silica nanoparticles (295 nm diameter) and epoxy-functionalized smaller silica nanoparticles (20 nm diameter). The so-realized macromolecular edifice leads to a hierarchical integration of nanoscale textures. Then hydrophobization of the last layer of amino-functionalized silica particles was carried out by grafting a new designed highly fluorinated aldehyde, creating a monomolecular layer via the formation of an imine function. Five highly fluorinated surfaces were built, and their water-repellent abilities were directly correlated to the surface topologies (i.e., the number of layers of silica nanoparticles and their organization on the glass support). The hydrophobicity increased with the number of layers and stable highly water-repellent surfaces (static contact angle with water of 150+/-3 degrees and a contact angle hysteresis of 12 degrees) were obtained with the alternation of nine layers. This result demonstrates the possibility to construct covalent LbL edifices with functionalized silica nanoparticles of different sizes and open this field for the elaboration of responsive, sensing, and therapeutic surfaces with improved film stability.

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.

Fabrication of Superhydrophobic PDMS Surfaces by Combining Acidic Treatment and Perfluorinated Monolayers

In this paper, polydimethylsiloxane (PDMS) with a superhydrophobic surface was generated by the combination of an acid corrosion followed by the covalent grafting of a highly fluorinated monolayer. The acid corrosion was performed with H2SO4 or HF, and the more effective was concentrated H2SO4. The resulting surface had a contact angle with water of 135 degrees. All the acid-treated samples were then functionalized by the covalent grafting of triethoxyaminopropylsilane followed by the reaction with semifluorinated acid chlorides, via the formation of an amide bond, or directly by a commercially available highly fluorinated silane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, to afford superhydrophobic surfaces (contact angle with water exceeding 160 degrees). The introduction of an amide function in the fluorinated monolayer afforded the best water repellency properties probably due to the organization induced by H-bonding between the surface grafted molecules.

Hydrocarbon versus Fluorocarbon in the Electrodeposition of Superhydrophobic Polymer Films

To elaborate on superhydrophobic surfaces, we report the electrochemical synthesis, surface morphology, and wettability of hydrocarbon conductive polymer films obtained by the electrodeposition of polythiophene, poly(3,4-ethylenedioxythiophene) (i.e., PEDOT), and poly(3,4-ethylenedioxypyrrole) (i.e., PEDOP) derivatives. Highly hydrophobic films were obtained from n-C(14)H(29) and n-C(8)H(17) chains in the cases of polythiophenes and PEDOP, respectively. By contrast, superhydrophobic films were formed by the deposition of PEDOT substituted with n-C(10)H(21) chains (PEDOT-methyl undecanoate): static contact angle ≈ 160.6°, hysteresis ≈ 2°, and sliding angle ≈ 3°. Their surface properties were compared to those of previously reported fluorinated analogues. The water-repellent properties of PEDOT-methyl undecanoate were similar to the best surface properties obtained with fluorinated monomers. Even if the main approach for the chemical factor to build up superhydrophobic surfaces is via a coating of a fluorinated compound, this work confirms that the formation of fractal surfaces is able to achieve super-anti-wetting properties within a hydrocarbon series (less expensive with a favorable ecotoxic approach), and it opens a new path to bioinspired surfaces.

Connector ability to design superhydrophobic and oleophobic surfaces from conducting polymers.

In the aim of creating superoleophobic surfaces using monomers with short perfluorinated chains, to avoid drawbacks associated with PFOA, original semifluorinated (C(4)F(9), C(6)F(13)) 3,4-ethylenedioxypyrrole derivatives were synthesized. These monomers were obtained using the faster synthetic method than previously described with some analogues, characterized and electrochemically polymerized on gold plates. The obtained surfaces exhibited superhydrophobic (contact angle with water of 157 degrees and 158 degrees, respectively) and oleophobic properties (contact angle with hexadecane: 88 degrees and 108 degrees, respectively). The comparison between these new monomers and already published analogue EDOP6 confirms the importance of the bipolaronic form of conductive polymer for obtaining surface nanoporosity and as a consequence improving surface oleophobicity. Thus, little change in the molecule design of the connector and the spacer of the monomer can have a significant influence on the surface oleophobicity.

Toxicity assessment of silica nanoparticles, functionalised silica nanoparticles, and HASE-grafted silica nanoparticles

Numerous nanomaterials have recently been developed, and numerous practical applications have been found in water treatment, medicine, cosmetics, and engineering. Associative polymers, such as hydrophobically modified alkali-soluble emulsion (HASE) systems are involved in several applications and have been extensively studied due to their ability to form three-dimensional networked gels. However, the data on the potential environmental effects of this polymers are scarce. The aim of this study is to assess the effect of functionalisation of silica nanoparticles, and coupling of functionalised silica nanoparticles to the associative polymer HASE on their toxicity. Thus, acute and chronic toxicity tests included a modified acute test (72 h) using daphnies, algae, and plants as model organisms. Gradient of toxicity varied with the tested organisms. Our results revealed that the functionalised nanoparticules and NP grafted polymer cause a global decrease in toxicity compared to commercial nanoparticule and HASE polymer.

Copolymerization of novel reactive fluorinated acrylic monomers with styrene: reactivity ratio determination

The radical copolymerization of three polymerizable surfactants with styrene was investigated by NMR spectroscopy to assess their compositions. The reactivity ratios of these monomers were calculated according to the methods of Fineman–Ross and Kelen–Tüdos. Consequently, Q and e values were deduced by the Alfrey and Price method. The results indicated the positive effect of the fluorine chain on the reactivity of monomers bearing a long spacer between the ammonium head and the acrylic function. These monomers exhibit high e values which are in favor of an intramolecular conformation of the surfactant where the ester carbonyl function of the polymerizable group interacts with the onium nitrogen atom via a compact six-sided structure.