Mélanie Emo

Role of Solvent and Effect of Substituent on Azobenzene Isomerization by Using Room-Temperature Ionic Liquids as Reaction Media.

The effects of a para substituent, as the electron-donating -OCH3 and -OtBu groups and the electron-withdrawing -Br and -F atoms, on azobenzene isomerization have been investigated in a series of imidazolium ionic liquids (BMIM PF6, BMIM BF4, BMIM Tf2N, EMIM Tf2N, BM2IM Tf2N, and HMIM Tf2N). The thermal cis-trans conversion tends to be improved in the presence of the substituent, as pointed out by the first-order rate constants measured at 25 °C. Both the rotation and the inversion mechanisms occur in BMIM Tf2N, EMIM Tf2N, and HMIM Tf2N, as highlighted by typical V-shape Hammett plots, but only rotation takes place in BMIM PF6, BMIM BF4, and BM2IM Tf2N. The possible interactions between the cation and the anion of the solvent and both the isomers of the azobenzene derivatives have been studied by small-wide-angle X-ray scattering (SWAXS). The calculated cis population in the photostationary state and the hardness parameter η of the trans isomer show that azobenzene and F-azobenzene are the less reactive molecules for the trans-cis conversion in all the investigated ionic liquids.

Triblock siloxane copolymer surfactant: template for spherical mesoporous silica with a hexagonal pore ordering.

Ordered mesoporous silica materials with a spherical morphology have been prepared for the first time through the cooperative templating mechanism (CTM) by using a silicone triblock copolymer as template. The behavior of the pure siloxane copolymer amphiphile in water was first investigated. A direct micellar phase (L(1)) and a hexagonal (H(1)) liquid crystal were found. The determination of the structural parameters by SAXS measurements leads us to conclude that in the hexagonal liquid crystal phase a part of the ethylene oxide group is not hydrated as observed for the micelles. Mesoporous materials were then synthesized from the cooperative templating mechanism. The recovered materials were characterized by SAXS measurements, nitrogen adsorption-desorption analysis, and transmission and scanning electron microscopy. The results clearly evidence that one can control the morphology and the nanostructuring of the resulting material by modifying the synthesis parameters. Actually, highly ordered mesoporous materials with a spherical morphology have been obtained with a siloxane copolymer/tetramethoxysilane molar ratio of 0.10 after hydrothermal treatment at 100 °C. Our study also supports the fact that the interactions between micelles and the hydrolyzed precursor are one of the key parameters governing the formation of ordered mesostructures through the cooperative templating mechanism. Indeed, we have demonstrated that when the interactions between micelles are important, only wormhole-like structures are recovered.

Monoolein Cubic Phase Gels and Cubosomes Doped with Magnetic Nanoparticles–Hybrid Materials for Controlled Drug Release

Hybrid materials consisting of a monoolein lipidic cubic phase (LCP) incorporating two types of magnetic nanoparticles (NP) were designed as addressable drug delivery systems. The materials, prepared in the form of a gel, were subsequently used as a macroscopic layer modifying an electrode and, after dispersion to nanoscale, as magnetocubosomes. These two LCPs were characterized by small-angle X-ray scattering (SAXS), cross-polarized microscopy, magnetic measurements, and phase diagrams. The magnetic dopants were hydrophobic NPoleic and hydrophilic NPcitric, characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM), and their influence on the properties of the cubic phases was investigated. The removal of the anticancer drug, Doxorubicin (Dox) from the hybrid cubic phase gels was studied by electrochemical methods. The advantages of incorporating magnetic nanoparticles into the self-assembled lipid liquid crystalline phases include the ability to address the cubic phase nanoparticle containing large amounts of drug and to control the kinetics of the drug release.

Metastable micelles and true liquid crystal behaviour of newly designed "cataniomeric'' surfactants

Jeffamines were used as molecular tools for the design of novel organized molecular systems based on so-called “cataniomeric” surfactants, which combine features of ionic liquids (ILs) and catanionic surfactants and which contain oligomeric building blocks. These systems show an original self-assembling behaviour in water, with a rich polymorphism: dynamic (or metastable) micelles and liquid crystals (cubic Im3m and Fm3m and hexagonal H1 phases). “Cataniomeric” surfactants were prepared by a simple acid–base reaction between oligomeric Jeffamine ED900 and various fatty acids (lauric, myristic, stearic and oleic acid) in a stoichiometric ratio, similar to well known salt-free catanionic surfactants. The phase behaviour was rationalized in terms of hydrocarbon chain length of the fatty counterion (equivalent carbon atoms, ECN) and of headgroup electrostatic interactions and flexibility. All synthesized surfactants show a direct micellar cubic phase, whose stability increases with hydrophobicity. A transition to a hexagonal phase takes place when ECN is higher than 29, and thus independently of the symmetry of the molecule. Thermal stability of the hexagonal phase also increases with ECN. An epitaxial transition of H1 → Im3m → Fm3m was also evidenced. These novel systems have straightforward applications in modern formulations or smart nanodevices, reversibly responsive to external stimuli.

A supramolecular hydrogel based on an original pseudopeptidic catanionic surfactant

A novel low-molecular weight gelator based on a mixture of a cationic pseudopeptidic surfactant and lauric acid (1/3), at basic pH, is reported. The gelling properties of this system have been investigated by Infra-Red spectroscopy (FT-IR), Scanning and Transmission Electron Microscopies (SEM, TEM), and Small Angle X-ray Scattering (SAXS).

Nanoparticle-free magnetic mesoporous silica with magneto-responsive surfactants

Magneto-responsivity can be imprinted in hard mesoporous silica materials using soft colloidal templates formed by magnetic surfactants. The materials exhibit a low to high spin transition due to geometrical constraints of the isolated iron ions grafted on the silica walls.

Investigation of a novel fluorinated surfactant-based system for the design of spherical wormhole-like mesoporous silica

In contrast to hydrogenated based systems that led to many studies, fluorinated surfactants have been little reported. Thanks to their high chemical and thermal stability, these compounds are considered as suitable candidates for the synthesis of porous materials with an enhanced hydrothermal stability. This study reports the synthesis of a new fluorinated surfactant, 2-trifluoromethyl-7,7,8,8,9,9,10,10,11,11,12,12,12-tridecafluoro-4-thia-1-dodecanoic acid (FSC) obtained from the thiol-ene radical addition of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanethiol onto 2-trifluoromethyl acrylic acid in 85% yield. In the aim of achieving micelles in water to design mesoporous materials according to the cooperative templating mechanism, FSC was modified with water-soluble telechelic diamine (Jeffamine) ED-600. The modified surfactant was deeply characterized by spectroscopic methods and the FSC-Jeffamine ED-600 micellar system was used as porogen to prepare mesoporous materials via the cooperative templating mechanism. Spherical wormhole-like mesostructured silica materials of high specific surface area (850m2/g) and homogeneous pore size distribution (ca. 3.4nm) were obtained by conveniently adjusting the porogen/silica molar ratio and the hydrothermal conditions.

Investigation of mixed fluorinated and triblock copolymer liquid crystals: Imprint for mesostructured bimodal silica

Due to the difference in «mutual phobicity» between fluorocarbon and hydrocarbon chains, mixtures of fluorinated and hydrogenated surfactants are excellent candidates to design bimodal systems having two types of mesopores. In literature, only a few papers deal with these bimodal systems. Here hexagonal liquid crystal mixtures of the polyoxyethylene fluoroalkyl ether [R(F)8(EO)9] and the Pluronic [P123] have been used to template this kind of mesostructure through the liquid crystal mechanism, which is barely considered. After the detailed investigation of the R(F)8(EO)9/P123/water liquid crystal domain, materials have been synthesized and characterized by small angle X-ray scattering, transmission electron microscopy and nitrogen adsorption-desorption analysis. Our results show that this system provides two separate pore sizes in the materials over the mesoporous range. The ratio between the small mesopores and the large ones depends on the proportion between the porogens in the mixture. Nonetheless, we also outline that a minimum quantity of silica is required to recover the two hexagonal networks.