Aggregates formed in an aqueous medium by three ionic liquids CnMImIbu made up of 1-alkyl-3-methyl-imidazolium cation (n = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), 1H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers.

Nous nous sommes intéressés à l’influence de la distribution de charge sur les interactions colloïdales. Nous avons formulé un système colloïdal modèle à base de microémulsions de décane dans l’eau, stabilisées par des tensioactifs non-ioniques (C12E5). Les gouttes de décane initialement neutres sont progressivement dopées par des tensioactifs de valence et de structure variables (Figure 1). Cette approche permet de faire varier la distribution de charge à la surface des colloïdes selon trois paramètres : le taux de charge , la valence v des tensioactifs (de 1 à 4) et la structure des tensioactifs (L pour linéaire ou B pour branché). Le taux de dopage  est défini comme la fraction molaire des groupes ioniques par rapport à toutes les têtes polaires des tensio-actifs présents. On peut le traduire en charge structurale Zstr des gouttelettes une fois que l’on a caractérisé leur taille et leur composition. Dans cette étude, Zstr varie de 0 à 50e (densité de charge de 0 à 0.12 e/nm2) et la fraction volumique est de 5%. La température correspond à celle de rupture d’émulsification et varie de 24°C à 27°C. Figure 1 : Particules colloïdales de charge structurale Zstr=12, obtenues en dopant des particules neutres par un cation monovalent 1, trivalent 3 ou tétravalent 4 et de structure linéaire L ou branchée B.Nous avons mis en évidence les interactions répulsives entre ces colloïdes par diffusion de rayonnement. Plus la charge structurale est grande plus la compressibilité osmotique (intensité à angle nul) diminue, comme prévu. Cependant pour une Zstr fixée, les microrémulsions dopées par des tensioactifs multivalents et branchés présentent une compressibilité S(0) plus élevée.Plusieurs interprétations sont possibles: la première considère une réduction de la charge effective Zeff par condensation des contre-ions. Des mesures potentiométriques à l’aide d’électrodes spécifiques aux ions bromure montrent que Zeff est effectivement plus faible que Zstr dans le cas des dopants de structure branchés. Cependant, cela ne suffit pas à expliquer la faiblesse des répulsions observées.

At the interface, as in the bulk, the Brownian motion rules the diffusion of colloids. The motor of the motion is the thermal energy kT; and the friction coefficient accounts for viscous dissipations at the interface. These physical conditions constrain the colloid to move following random walk trajectories. To observe directional trajectories, overcoming the limitation of Brownian motion, we have investigated Janus Silica-Platinum active colloids. The catalytic motor of the motion in our case is provided by the Platinum face, on which H2O2 (the fuel) decomposes into oxygen gas and water. To study the motion at the interface we have used a particle-tracking video-microscopy method. We start presenting the results on the motion of Silica colloids (Radius = 1 µm) at air-water interface. Then we describe the fabrication of Janus Silica-Platinum colloids. Presenting the results on the active motion, we discuss the effect of H2O2 fuel concentration and the competition between directional and Brownian motion.

This study deals with the ionically-driven self-assembly of oligomeric aminosilicones, judiciously protonated with a variety of organic acids. Depending on the length of the silicone and the strength of the associated acids, (inverse) water-in-silicone emulsions, small nanoparticles, or catanionic vesicles were prepared and characterized by conventional (TEM) or original (DIC optical microscopy, DOSY NMR) techniques. For chains longer than about 40 units, a specific PEG-based sulfonic acid was synthesized and used to generate a supramolecular block-like copolymer and ensure fast and efficient emulsification. In all instances, a simple impulse such as pH increase triggered phase separation of the colloidal objects.

We report theoretical predictions and measurements of the capillary force acting on a spherical colloid smaller than the capillary length that is placed on a curved uid interface of arbitrary shape. By coupling direct imaging and interferometry, we are able to measure the in situ colloid contact angle and to correlate its position with respect to the interface curvature. Extremely tiny capillary forces down to femto-Newton can be measured with this method. Measurements agree well with a theory relating the capillary force to the gradient of Gaussian curvature and to the mean curvature of the interface prior to colloidal deposition. Numerical calculations corroborate these results.

The water dispersion of luminescent nanocrystals (NCs) synthesized in organic solvent by encapsulation in a surfactant bilayer is a promising strategy for preserving the optical properties of NCs. The phase transfer of highly monodispersed ZnO NCs using the monomer, dimer, trimer and polymer of a series of alkyl ammonium surfactants is compared. Transfer yields over 60% could be obtained with the oligomers and the polymer. In contrast, we observed no measurable transfer using the single chain surfactant. NMR spectroscopy, including DOSY and NOESY, demonstrated that increasing the oligomerization number ameliorates the stability within the coating bilayer. The NCs exhibit a strong luminescence in water and show long term chemical and photo-chemical stability.

The synthesis and the aggregation behavior of novel well-defined poly(N,N-diethylacrylamide)-b-poly- (L-lysine) (PDEAm-b-PLL) double hydrophilic block copolymers are reported. PDEAm-b-PLL was prepared using an original strategy which consisted of the ring opening polymerization (ROP) of N3- trifluoroacetyl-L-lysine N-carboxyanhydride using terminated-thiol PDEAm as a macroinitiator. After deprotection of the amine group of the L-lysine, pH- and thermo-sensitive poly(N,N-diethylacrylamide)- b-poly(L-lysine) block copolymers were obtained. The structure of the copolymers was characterized by 1H NMR and FT-IR. Then, pH and temperature sensitivities were measured by 1H NMR and UV/Vis spectroscopy. At different pH values and temperatures, poly(L-lysine) and poly(N,N-diethylacrylamide) showed typical behaviors, which led to different types of aggregation in aqueous solution. The influence of both stimuli was carefully investigated by DLS, TEM, and SANS.