Samba Yandé Dieng

Superhydrophobic (low adhesion) and parahydrophobic (high adhesion) surfaces with micro/nanostructures or nanofilaments.

Controlling the water adhesion is extremely important for various applications such as for water harvesting. Here, superhydrophobic (low adhesion) and parahydrophobic (high adhesion) substrates are both obtained from hydrophilic polymers. We show in the work that a judicious choice in the monomer structure used for electropolymerization can lead to these two properties. Using a phenyl group, parahydrophobic properties are reached due to the formation of nanofilaments. By contrast, using a naphthalene or a biphenyl group, superhydrophobic properties are obtained due the formation of both micro- and nanostructures.

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.

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.

Superhydrophobic and oleophobic surfaces containing wrinkles and nanoparticles of PEDOT with two short fluorinated chains

Superhydrophobic and oleophobic surfaces are obtained by electrodeposition of original PEDOT derivatives containing two short fluorinated chains. The liquid-repellent properties are due to the combination of high intrinsic hydrophobicity and oleophobicity of polymers due the presence of two fluorinated chains, and the formation of wrinkles and spherical particles induced by the electrodeposition process. The presence of wrinkles and spherical particles and as a consequence the surface hydrophobicity and oleophobicity is correlated to the fluorinated chain length and electrochemical parameters (the deposition charge for the depositions at constant potential and the scan rate and number of scans for the depositions by cyclic voltammetry). Here, the increase in the number of wrinkles and spherical particles induces an increase in the surface roughness increasing especially the surface hydrophobicity while the surface oleophobicity is not always affected. However, it is also possible to increase the surface oleophobicity by a careful choice in the electrochemical parameters. This work also allows the elaboration of super liquid-repellent surfaces with low fluorine content (materials with low bioaccumulative potential).

Formation of Nanofibers with High Water Adhesion by Electrodeposition of Films of Poly(3,4‐ethylenedioxypyrrole) and Poly(3,4‐propylenedioxypyrrole) Substituted by Alkyl Chains

With the aim of controlling the surface hydrophobicity and water adhesion, nanofibrous surfaces were prepared by electropolymerization of 3,4-ethylenedioxypyrrole (EDOP) and 3,4-propylenedioxypyrrole (ProDOP) derivatives having various alkyl chains (C3 to C17 ) grafted to a 3,4-alkylenedioxy bridge. Depending on whether an EDOP or a ProDOP was used, and the length of the alkyl chain, the surface properties of the resulting polymer were very different. The formation of nanofibrous surfaces was much more favored for ProDOP derivatives. The alkyl chain length has also a huge influence on the formation of nanofibers, and alkyl chains of intermediate length (C9 and C11 ) gave the best results. Apparent contact angles (θw ) of up to 150° were obtained, and the water adhesion properties were highly variable. This work is important for many applications in which the control of interaction forces with a medium is required, such as in oil-water separation membranes or water-harvesting systems.

Surface Nanostructuration and Wettability of Electrodeposited Poly(3,4-ethylenedioxypyrrole) and Poly(3,4-propylenedioxypyrrole) Films Substituted by Aromatic Groups

In the aim to obtain parahydrophobic materials (both high contact angles and high hysteresis) for possible applications in water harvesting systems, we report the synthesis of novel 3,4-ethylenedioxypyrrole (EDOP) and 3,4-propylenedioxypyrrole (ProDOP) monomers with aromatic rings on the 3,4-alkylenedioxy bridge and the resulting conducting polymer films were prepared by electropolymerization. We show that the surface properties can be tuned by the nature of the aromatic ring (phenyl, biphenyl, diphenyl, naphthalene, fluorene, and pyrene) and the polymerizable core (EDOP or ProDOP). The best results are obtained with both EDOP and diphenyl, with which extremely high hydrophobic properties (up to 116°) are obtained, even if the polymers are intrinsically hydrophilic. These surfaces could be applied in the future, for example, in water harvesting systems or in water/oil separation membranes. The synthesis strategy is extremely interesting, and many other molecules will be envisaged in the future.