Alioune Diouf

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.

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 Molecular Dynamics Study on the Miscibility of Polyglycolide with Different Polymers

The miscibility of mixtures between polyglycolide and the following polymers: polyethylene, polystyrene, polyacrylonitrile and polylactide is studied by Molecular Dynamics Simulation using Forcite and Blends Modules. The simulations of the binary mixture for the evaluation of the energy is achieved in the framework of the Flory-Huggins model. The Flory-Huggins interaction parameter, the mixing energy and the phase diagrams are analyzed and found to be the main parameters and features controlling the miscibility process in the present computer simulations. The results of the simulation show that when the Flory-Huggins interaction parameter Chi to a value close to 1 of mixtures the polyglycolide / polylactide, polyglycolide / polyacrylonitrile, polyglycolide / polyethylene and polyglycolide / polystyrene are miscible at 50K, 230K, 238K and 378K respectively. The commonly-accepted miscibility criteria of the binary namely mixing when Chi is negative or positive but small and non-miscibility when Chi is positive and higher than 1 is used in the present analysis. This led to the evaluation of a mixing energy of 1.5kcal/mole. The phase diagrams of all the binary mixtures are similar and present one critical point. The miscibility of the binary mixtures at that critical point corresponds to an optimal mole fraction of 0.5 but for different temperature for each binary mixture. In fine, the polyglycolide is miscible with polylactide for all the temperature range and above 378K for polyacrylonitrile, polyethylene and polystyrene. The results obtained are in agreement with those found in the literature.

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.

Computer Simulation of the Dielectrics Properties in the Dense Circles

To investigate the dielectric properties in the dense circles a program based on the Lorentz model is implemented. So, to understand the importance of the certain physical parameters (spectral width, specific pulsation and the number of particle) on the dielectric properties of the dense media, one varied these parameters to observe their influence on the real and imaginary susceptibility as well as the indication of the environment. Besides knowing that the Drude model is a particular case of the Lorentz model, a comparative investigation has been done to observe their behavior according to certain parameters.