We present a series of experiments, using different techniques such as light scattering, conoscopy, neutron scattering and microscopic observations, to determine the orientation of lyotropic lamellar phases under shear. Three states of orientation are observed, depending upon both the shear rate and the inter-membrane separation. These steady states are separated by dynamic transitions. Among the states described, we focus our attention on a state made of monodisperse close-packed multilayered vesicles whose size is precisely fixed by the shear rate

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The rheological behaviour of lyotropic lamellar phases is studied as a function of the membrane repeating distance. The steady-state rheology is described as a consequence of the so-called orientation diagram described previously. Three distinct regions of Werent orientations are described, which are separated by two out-of-equilibrium transitions. We show that these transitions can be either discontinuous (subcritical) or continuous. In one of these transitions, one can go continuously from one regime to the other through a bifurcation point.

Ionic liquids (ILs) are a new class of organic solvents that are stable over a large range of temperatures and have negligible vapor pressures.[1] Owing to their molecular structure, associating a cation and an anion, their physicochemical properties can be easily modulated by changing one of the ions. Ionic liquids are now widely used in organic synthesis and chemical separations due to their high solvation ability and their tuneable nature. [2,3] Almost unexplored, surfactant organization in ILs could open new research directions towards micellar catalysis into IL media, solvation enhancement for apolar entities and lyotropic properties. Indeed, surfactant organization occurs in some nonaqueous solvents [4,5] and is largely used in aqueous systems for drug vectorization, catalysis, gelification and other applications.[5] Recently, microemulsions have been obtained in IL-oil mixtures [6] and only premicellar aggregation has been detected in pure ILs. [7,8] However, no clear demonstration of the existence of a micellar phase in ILs has been reported yet.Here, we describe the behavior of a series of pure alkyl poly-(oxyethyleneglycol) ethers in 1-butyl-3-methyl-imidazolium (bmim) ILs with various counter ions [BF 4 À , PF 6 À and Tf 2 N À , that is, bis(trifluoromethylsulfonyl)amide; Figure 1]. The choice of nonionic surfactants, denoted C n E m (n = 12-16; m = 4-8), was justified to avoid the exchange of counter ions with the solvent. For high concentrations of surfactant (ca. 1 mol L À1 ), the mixtures C n E m /bmimBF 4 were generally solid at room temperature with a cloud point at high temperature (see Supporting Information). Herein, all experiments were performed at 25 8C with concentrations lower than 1 mol L À1, at which the mixtures were all limpid and homogeneous.Surface tension measurements were performed to probe the aggregation behavior of the surfactants in bmimBF 4 . For all the selected surfactants, the surface tension of the C n E m /bmimBF 4 solutions decreased when the surfactant concentration increased (Figure 2). This indicated their adsorption at the air/solution interface. The Szyszowski-Langmuir adsorption equation [9] fitted well this decrease, leading to an estimation of the area per molecule of the surfactant at the air/bmimBF 4 interface, that occurred to be comparable or lower than the ones found at the air/water interface (Table 1). Those differences between bmimBF 4 and water may be related to a change in the organization and/or solvation state of the adsorbed surfactants. In bmimBF 4 like in water, the molecular area of the surfactant decreased with increasing alkyl chain length or decreasing number of oxyethylene groups.This initial decrease of the surface tension is followed by an abrupt change in the slope of the surface tension versus C (Figure 3; semi-log plot). After this breaking point, the surface tension of the solutions remains more or less constant. Such a behavior suggested the formation of micelles within the ILs, where the break point corresponds to a critical micelle...

A quaternary system made of an ionic surfactant (SDS), octanol, water and sodium chloride has been investigated. We present experimental results that demonstrate the existence of a phase of vesicles at thermal equilibrium. We show that vesicles can be prepared both in a dilute regime leading to an isotropic liquid phase of low viscosity and in a concentrated regime leading to a phase of close packed vesicles (probably multilayered) exhibiting high viscosity and viscoelasticity

Graphene oxide (GO), the main precursor of graphene-based materials made by solution processing, is known to be very stiff. Indeed, it has a Young's modulus comparable to steel, on the order of 300 GPa. Despite its very high stiffness, we show here that GO is superflexible. We quantitatively measure the GO bending rigidity by characterizing the flattening of thermal undulations in response to shear forces in solution. Characterizations are performed by the combination of synchrotron X-ray diffraction at small angles and in situ rheology (rheo-SAXS) experiments using the high X-ray flux of a synchrotron source. The bending modulus is found to be 1 kT, which is about two orders of magnitude lower than the bending rigidity of neat graphene. This superflexibility compares with the fluidity of self-assembled liquid bilayers. This behavior is discussed by considering the mechanisms at play in bending and stretching deformations of atomic monolayers. The superflexibility of GO is a unique feature to develop bendable electronics after reduction, films, coatings, and fibers. This unique combination of properties of GO allows for flexibility in processing and fabrication coupled with a robustness in the fabricated structure.graphene oxide | bending rigidity | rheo-SAXS

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