Microrheology of gemini surfactants at interfaces and in solutions in the dilute and semidilute regimes.

Gemini surfactants are ideal systems to study a wide range of rheological behaviours in soft matter, showing fascinating analogies with living polymers and polyelectrolytes. By only changing the concentration, the shear viscosity can vary by 7 orders of magnitude in the bulk when transitioning through the semidilute regime. In order to elucidate on the intrinsic shear viscosity profile at the interface in soft matter systems manifesting various concentration regimes and morphological transitions, we performed microrheology and adsorption experiments under a wide range of experimental conditions.

Efficacy of leupeptin in treating ischemia in a rat hind limb model.

Prolonged tourniquet use can lead to tissue ischemia and can cause progressive muscle and nerve injuries. Such injuries are accompanied by calpain activation and subsequent Wallerian-like degeneration. Several known inhibitors, including leupeptin, are known to impede the activity of calpain and associated tissue damage.

Sunflower Proteins at Air-Water and Oil-Water Interfaces.

The adsorption of a sunflower protein extract at two air-water and oil-water interfaces is investigated using tensiometry, dilational viscoelasticity, and ellipsometry. For both interfaces, a three step mechanism was evidenced thanks to master curve representations of the data taken at different aging times and protein concentrations. At short times, a diffusion limited adsorption of proteins at interfaces is demonstrated.

pH-mediated control over the mesostructure of ordered mesoporous materials templated by polyion complex micelles.

Ordered mesoporous silica materials were prepared under different pH conditions by using a silicon alkoxide as a silica source and polyion complex (PIC) micelles as the structure-directing agents. PIC micelles were formed by complexation between a weak polyacid-containing double-hydrophilic block copolymer, poly(ethylene oxide)--poly(acrylic acid) (PEO--PAA), and a weak polybase, oligochitosan-type polyamine. As both the micellization process and the rate of silica condensation are highly dependent on pH, the properties of silica mesostructures can be modulated by changing the pH of the reaction medium.

Multistep building of a soft plant protein film at the air-water interface.

Gliadins are edible wheat storage proteins well known for their surface active properties. In this paper, we present experimental results on the interfacial properties of acidic solutions of gliadin studied over 5 decades of concentrations, from 0.001 to 110 g/L.

Janus Colloids Actively Rotating on the Surface of Water.

Biological or artificial microswimmers move performing trajectories of different kinds such as rectilinear, circular, or spiral ones. Here, we report on circular trajectories observed for active Janus colloids trapped at the air-water interface. Circular motion is due to asymmetric and nonuniform surface properties of the particles caused by fabrication.

Complexation of short ds RNA/DNA oligonucleotides with Gemini micelles: a time resolved SAXS and computational study.

Gene therapy is based on nucleic acid delivery to pathogenic cells in order to modulate their gene expression. The most used non viral vectors are lipid-based nanoaggregates, which are safer than viral carriers and have been shown to assemble easily with both DNA and RNA. However, the transfection efficiency of non viral carriers still needs to be improved before intensive practise in clinical trials can be implemented.

MHz Ultrasound Induced Roughness of Fluid Interfaces.

The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In the absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface roughness of liquid-gas and liquid-liquid interfaces.

Translational viscous drags of an ellipsoid straddling an interface between two fluids.

We study the dynamics of individual polystyrene ellipsoids of different aspect ratios trapped at the air-water interface. Using particle tracking and in situ vertical scanning interferometry techniques we are able to measure translational drags and the protrusion in air of the ellipsoids. We report that translational drags on the ellipsoid are unexpectedly enhanced: despite the fact that a noticeable part of the ellipsoid is in air, drags are found larger than the bulk one in water.

Wetting and orientation of catalytic Janus colloids at the surface of water.

Janus colloidal particles show remarkable properties in terms of surface activity, self-assembly and wetting. Moreover they can perform autonomous motion if they can chemically react with the liquid in which they are immersed. In order to understand the self-propelled motion of catalytic Janus colloids at the air-water interface, wetting and the orientation of the catalytic surface are important properties to be investigated.

Multiwalled Carbon Nanotube/Cellulose Composite: From Aqueous Dispersions to Pickering Emulsions.

A mild and simple way to prepare stable aqueous colloidal suspensions of composite particles made of a cellulosic material (Sigmacell cellulose) and multiwalled carbon nanotubes (MWCNTs) is reported. These suspensions can be dried and redispersed in water at pH 10.5.

Method to disperse lipids as aggregates in oil for bilayers production.

Several techniques to assemble artificial lipid bilayers involve the zipping of monolayers. Their efficiency is determined by the renewal of the saturated monolayers to be zipped and this proceeds by adsorption of lipids dispersed in oil as aggregates. The size of these lipids aggregates is a key parameter to ensure both the stability of the suspension and a fast release of lipids at the interface.

Drug-Polymer Electrostatic Complexes as New Structuring Agents for the Formation of Drug-Loaded Ordered Mesoporous Silica.

Using aminoglycoside antibiotics as drug models, it was shown that electrostatic complexes between hydrophilic drugs and oppositely charged double-hydrophilic block copolymers can form ordered mesophases. This phase behavior was evidenced by using poly(acrylic acid)-block-poly(ethylene oxide) block copolymers in the presence of silica precursors, and this allowed preparing drug-loaded mesoporous silica directly from the drug-polymer complexes. The novel synthetic strategy of the hybrid materials is highly efficient, avoiding waste and multistep processes; it also ensures optimal drug loading and provides pH-dependence of the drug release from the materials.

Enhanced active motion of Janus colloids at the water surface.

We have investigated the active motion of self-propelled colloids confined at the air-water interface and explored the possibility of enhancing the directional motion of self-propelled Janus colloids by slowing down their rotational diffusion. The two dimensional motion of micron-sized silica-platinum Janus colloids has been experimentally measured by particle tracking video-microscopy at increasing concentrations of the catalytic fuel, i.e.

Brownian diffusion of a partially wetted colloid.

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk.

Electrostatic interaction between nonuniformly charged colloids: experimental and numerical study.

The influence of the surface charge distribution on the interaction between nanosized particles in water is reported. The distribution of charges at the surface of initially neutral microemulsion droplets has been modulated by additions of various oligomeric cationic surfactants. The osmotic compressibility of the doped microemulsions was measured by light and small-angle neutrons scattering and reveals that the overall effective interaction induced by the ionic groups is repulsive.

In situ assessment of the contact angles of nanoparticles adsorbed at fluid interfaces by multiple angle of incidence ellipsometry.

Here multiple angle of incidence ellipsometry was successfully applied to in situ assess the contact angle and surface coverage of gold nanoparticles as small as 18 nm, coated with stimuli-responsive polymers, at water-oil and water-air interfaces in the presence of NaCl and NaOH, respectively. The interfacial adsorption of the nanoparticles was found to be very slow and took days to reach a fairly low surface coverage. For water-oil interfaces, in situ nanoparticle contact angles agree with the macroscopic equilibrium contact angles of planar gold surfaces with the same polymer coatings, whilst for water-air interfaces, significant differences have been observed.

Time resolved SAXS to study the complexation of siRNA with cationic micelles of divalent surfactants.

The complexation of siRNA (small interfering RNA) with cationic micelles was studied using time dependent synchrotron SAXS. Micelles were formed by two types of divalent cationic surfactants, i.e.

Surfactant behavior of ionic liquids involving a drug: from molecular interactions to self-assembly.

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), (1)H 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.

Capillary force on a micrometric sphere trapped at a fluid interface exhibiting arbitrary curvature gradients.

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 fluid 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 femtonewtons can be measured with this method.

Supramolecular organization of protonated aminosilicones in water.

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.

Hybrid polyion complex micelles formed from double hydrophilic block copolymers and multivalent metal ions: size control and nanostructure.

Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al(3+), La(3+), or Al(13)(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation.

Growth and branching of charged wormlike micelles as revealed by dilution laws.

The successive transitions of morphology in aqueous solutions of interacting micelles are directly evidenced by the position q* of the correlation peak of the small angle neutron scattering profiles. As the volume fraction Phi increases, q* successively fits to the dilution laws expected for spheres and cylinders, and eventually gets close to the one expected for sheets when the micelles get branched. Data in between the swelling laws are quantitatively analyzed in terms of aggregation number and junction density.