Experimental Characterization of Droplet Adhesion: The Ejection Test Method (ETM) Applied to Surfaces with Various Hydrophobicity.

We study the wetting and the adhesive behavior of substrates made by electropolymerization of copolymers of pyrene substituted with fluoroalkyl and adamantyl groups. The hydrophobicity and water adhesion properties can be tuned by the molar percentage (mol %) of each pyrene monomer so that the substrate properties can vary from superhydrophobic to parahydrophobic, with respectively low and high water adhesion. The ejection test method (ETM) is proposed as an original tool to discriminate and characterize such substrates. Using a catapult-like apparatus, a droplet initially at rest on the surface is subject to a large acceleration and is subsequently ejected. Depending on the surface properties and initial catapult acceleration, the ejection is more or less efficient and occurs with or without fragmentation of the droplet. The ETM is shown to be a complementary test to the lateral adhesion and hysteresis classical measurements. This work is of importance for the understanding of adhesion phenomena on various surfaces and for a better quantitative characterization of their adhesive properties.

One F-octyl versus two F-butyl chains in surfactant aggregation behavior.

An easy synthetic procedure in two or three steps from perfluoroalkylethyl iodide derivatives led to six novel fluorinated carboxylates monomeric and gemini surfactants with one or two hydrophobic tails, respectively: RF(C2H4)CH(CO2(-))2,2Na(+) and [RF(C2H4)]2C(CO2(-)),Na(+), where RF = C4F9, C6F13, and C8F17. These anionic surfactants exhibited very low surface tension from 15 to 33 mN/m as well as low critical micelle concentration until 1.3 × 10(-4) mol/L. Furthermore, the surface properties of the gemini compound with two short fluoroalkyl chains (RF = C4F9) were found to be almost equal to those of the monomeric surfactant with one long fluoroalkyl chain (RF = C8F17), which could provide an interesting alternative to the bioaccumulative long-chain perfluorinated surfactant.

A bioinspired approach to fabricate fluorescent nanotubes with strong water adhesion by soft template electropolymerization and post-grafting.

HYPOTHESIS: In this original work, we aim to control both the surface wetting and fluorescence properties of extremely ordered and porous conducting polymer nanotubes prepared by soft template electropolymerization and post-grafting. For reaching this aim, various substituents of different hydrophobicity and fluorescence were post-grafted and the post-grafting yields were evaluated by surface analyses. We show that the used polymer is already fluorescent before post-grafting while the post-grafting yield and as a consequence the surface hydrophobicity highly depend on the substituent. EXPERIMENTS: Here, we have chosen to chemically grafting various fluorinated and aromatic substituents using a post-grafting in order to keep the same surface topography. Flat conducting polymer surfaces with similar properties have been also prepared for determining the surface energy with the Owens-Wendt equation and estimating the post-grafting yield by X-ray Photoemission Spectroscopy (XPS) and Time of Flight Secondary Emission Spectrometry (ToF-SIMS). For example, using fluorinated chains of various length (C4F9, C6F13 and C8F17), it is demonstrated that the surface hydrophobicity and oleophobicity do not increase with the fluorinated chain length due to the different post-grafting yields and because of the presence of nanoroughness after post-grafting. FINDINGS: These surfaces have high apparent water contact angle up to 130.5° but also strong water adhesion, comparable to rose petal effect even if there are no nanotubes on petal surface. XPS and ToF-SIMS analyses provided a detailed characterisation of the surface chemistry with a qualitative classification of the grafted surfaces (F6 > F4 > F8). SEM analysis shows that grafting does not alter the surface morphology. Finally, fluorescence analyses show that the polymer surfaces before post-treatment are already nicely fluorescent. Although the main goal of this paper was and is to understand the role of surface chemistry in tailoring the wetting properties of these surfaces rather than provide specific application examples, we believe that the obtained results can help the development of specific nanostructured materials for potential applications in liquid transport, or in stimuli responsive antimicrobial surfaces.

Giant brainlike aggregates from new fluorocarbon/hydrocarbon hybrid cationic surfactants.

A rapid synthetic procedure in two steps from perfluoroalkylethyl iodide derivatives led to 18 novel ammonium type hybrid surfactants of the general formula: R(F)(CH(2))(2)S(CH(2))(2)N(+)(CH(3))(2)R(H)Br(-) (R(F) = C(4)F(9), C(6)F(13), C(8)F(17); R(H) = C(4)H(9), C(6)H(13), C(8)H(17), C(10)H(21), C(12)H(25), C(14)H(29)). These hybrid surfactants exhibited very low surface tension (from 16 to 25 mN/m) as well as low critical micellar concentration until 1.5 × 10(-5) mol/L. A special focus was made on aggregation phenomenon as giant multilamellar "brainlike" vesicles were observed via cryogenic scanning electron microscopy (cryoSEM) and transmission electron microscopy (TEM; with a contrast agent) suggesting a high encapsulation ability and a very important specific surface of these particular organizations.

Micellar formation by soft template electropolymerization in organic solvents.

HYPOTHESIS: The formation of porous nanostructures on surfaces and the control of their size and shape is fundamental for various applications. The creation of nanotubes is particularly difficult to implement without the aid of hard and rigid templates. Recently, methods that form nanotubular structures in a straightforward manner and without direct templating, e.g. soft templating, have been highly sought after. Here we propose the use of "soft templating" via self-assembly of conducting monomers during electropolymerization in organic solvents as a mean to form porous, nanotubular features. EXPERIMENTS: Naphtho[2,3-b]thieno[3,4-e][1,4]dioxine (NaphDOT) is employed as monomer for electropolymerizations conducted in dichloromethane and chloroform containing varying amounts of water. SEM analyses of the resulting surfaces confirms the strong capacity of NaphDOT to form vertically aligned nanotubes. Polymerization solutions analyzed by DLS and TEM reveal the presence of micelles prior to electropolymerization, and the size of the micelles correlates with the inner diameter of the nanotubes formed. FINDINGS: We show that micelles in polymerization solutions are stabilized by both monomers and electrolytes. We propose a mechanism where reverse micelles are forming a soft-template responsible for the formation of porous nanostructures during electropolymerization in organic, non-polar solvents. In this mechanism, the monomer and electrolyte assume the role of surfactant in the reverse micelle system.

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.

Cupric Oxide Nanostructures from Plasma Surface Modification of Copper.

Taking inspiration from the hydrophilic and superhydrophilic properties observed from the nanostructures present on the leaves of plants such as Alocasia odora, Calathea zebrina, and Ruelia devosiana, we were able to synthesize cupric oxide (CuO) nanostructures from the plasma surface modification of copper (Cu) that exhibits hydrophilic and superhydrophilic properties. The Cu sheets were exposed to oxygen plasma produced from the P300 plasma device (Alliance Concept, Cran-Gevrier, France) at varying power, irradiation times, gas flow rates, and pulsing duty cycles. The untreated and plasma-treated Cu sheets were characterized by contact angle measurements, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to determine the changes in the surface of Cu before and after plasma treatment. Results showed that plasma-treated Cu sheets exhibited enhanced wetting properties compared to untreated Cu. We attributed the decrease in the measured water contact angles after plasma treatment to increased surface roughness, formation of CuO nanostructures, and transformation of Cu to either CuO2 or Cu2O3. The presence of the CuO nanostructures on the surface of Cu is very useful in terms of its possible applications, such as: (1) in antimicrobial and anti-fouling tubing; (2) in the improvement of heat dissipation devices, such as microfluidic cooling systems and heat pipes; and (3) as an additional protection to Cu from further corrosion. This study also shows the possible mechanisms on how CuO, CuO2, and Cu2O3 were formed from Cu based on the varying the plasma parameters.

Functionalized and grafted TiO2, CeO2, and SiO2 nanoparticles-ecotoxicity on Daphnia magna and relevance of ecofriendly polymeric networks.

Effects of functionalization and grafting of TiO2, CeO2, and SiO2 nanoparticles (NPs) were investigated, and toxicity of pristine, functionalized, and grafted NP towards Daphnia magna was measured. Surface functionalization of NP with amine groups decreased hydrophobicity of NP. When NPs were hydrophilic, they were less toxic than hydrophobic NP towards D. magna. Grafting agents influenced toxicity: no toxicity of NP was observed when bio-based and hydrogenated synthetic polymers were used, whereas perfluorinated polymers induced a higher toxicity.

Barrier cream based on CeO2 nanoparticles grafted polymer as an active compound against the penetration of organophosphates.

Due to their small size, nanoparticles possess unique properties. Cerium oxide nanoparticles have been already studied for their capacity to adsorb and neutralize toxic compounds including organophosphates. By covalently grafting these nanoparticles to a thickening polymer, their potential aggregation resulting in a loss of surface area and their potential toxicity are avoided. Indeed, copolymers easily form gels in water at neutral pH thanks to low interactions occurring between polymeric chains; thus, gels can be spread on membrane supports to afford protective barriers. However, as we demonstrated previously, a formulation step of these hydride nanoparticle-polymeric compounds is necessary to overcome the cracking of the coating during drying. This work reports the impact of many factors on the efficiency of a new active Topical Skin Protectant (aTSP) including: (1) the presence of CeO2 nanoparticles in the protective coating and their amount, (2) their grafting to a perfluorocarbon thickening polymer and (3) the formulation of the CeO2 nanoparticle-grafted polymer. The combination of all the benefit parameters led to a very effective new aTSP against paraoxon penetration. The major in vitro diffusion studies were performed in Franz-type diffusion cells on two artificial membranes (silicone and Strat-M) and final validation on ex vivo human skin. The comparison of 24 h-exposure between membrane results indicated a difference in the behavior between the two artificial supports and the biological model; Strat-M membranes seeming closer to human skin results. Therefore, positive results regarding occlusive conditions should be confirmed with human skin.

New CeO2 nanoparticles-based topical formulations for the skin protection against organophosphates.

To reinforce skin protection against organophosphates (OPs), the development of new topical skin protectants (TSP) has received a great interest. Nanoparticles like cerium dioxide (CeO2) known to adsorb and neutralize OPs are interesting candidates for TSP. However, NPs are difficult to disperse into formulations and they are suspected of toxicological issues. Thus, we want to study: (1) the effect of the addition of CeO2 NPs in formulations for the skin protection (2) the impact of the doping of CeO2 NPs by calcium; (3) the effect of two methods of dispersion of CeO2 NPs: an O/W emulsion or a suspension of a fluorinated thickening polymer (HASE-F) grafted with these NPs. As a screening approach we used silicone membranes as a skin equivalent and Franz diffusion cells for permeation tests. The addition of pure CeO2 NPs in both formulations permits the penetration to decrease by a 3-4-fold factor. The O/W emulsion allows is the best approach to obtain a film-forming coating with a good reproducibility of the penetration results; whereas the grafting of NPs to a thickener is the best way to obtain an efficient homogenous suspension of CeO2 NPs with a decreased of toxicological impact but the coating is less film-forming which slightly impacts the reproducibility of the penetration results.

A spiral designed surface based on amino-perylene grafted polyacrylic acid.

This communication shows the possibility of inducing spontaneous special surface organisation by means of grafting a fluorescent aminobenzo[g,h,i]perylene derivative onto surface grown polyacrylic chains.

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.

Investigation of structure-surface properties relationship of semi-fluorinated polymerizable cationic surfactants.

Novel hybrid hydrocarbon/fluorocarbon ammonium type surfactant monomers (surfmers) of the general formula RF (CH2)l N(CH3)2(CH2)mOCOCH=CH2 with (RF=C4F9, C6F13, C8F17, l=4, 6, 11, and m=2-11) were synthesized and characterized. They exhibit very low surface tension as well as low critical micellar concentrations down to 1.39×10(-5)mol/L. Special attention was focused on theeffect of the polymerizable moiety, the length of the hydrocarbon spacers, and the fluorinated chains on surface activities of the reactive surfactants as compared to hydrocarbon surfmer analogs. Results indicate that the acrylic function has a pronounced effect on increasing the hydrophobic micelle character. This was confirmed by surface tensions and average surfaces occupied by these molecules at the water-gas interface. The micellar sizes were investigated by dynamic light scattering.

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.

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.

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.

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.