We study the nonlinear rheology of a novel class of transient networks, made of surfactant micelles of tunable morphology reversibly linked by block copolymers. We couple rheology and time-resolved structural measurements, using synchrotron radiation, to characterize the highly nonlinear viscoelastic regime. We propose the fluctuations of the degree of alignment of the micelles under shear as a probe to identify a fracture process. We show a clear signature of a brittle-to-ductile transition in transient gels, as the morphology of the micelles varies, and provide a parallel between the fracture of solids and the fracture under shear of viscoelastic fluids.

We report on a continuous droplet interface crossing encapsulation (cDICE) technique for the high-yield production of microscopic vesicles tunable in size and content. Overcoming some of the current technique limitations, such a simple setup has a great potential in various fields from encapsulation to the design of biomimetic cells and artificial tissues.

We study the nematic-smectic phase transition of a thermotropic liquid crystal confined to a spherical shell. Far from the nematic-smectic phase transition temperature, TNS, we observe a configuration with four þ1=2 defects, as predicted by theory. Since in this case K1 ~~ K3, the four defects are confined at the thinnest part of the shell to minimize the energy associated with the defect cores. By contrast, near TNS, where K3 >> K1, bend distortions become prohibited and the defects organize themselves along a great circle of the sphere, confirming recent theoretical and simulation results. During this structural change, the defects associate in two pairs that behave independently. In the smectic phase, we observe a new configuration displaying curvature walls.

The rheological properties of associative polymers (APs) are modified by the presence of surfactants, but little is known about the influence of surfactants on the structure of selfassociated aggregates in aqueous media. Using small-angle neutron scattering (SANS), the structure of self-assembled aggregates of a series in concentration of telechelic poly(ethylene oxide) (M ≈ 20 000 g mol 1) end-capped by hydrocarbon or of fluorocarbon groups in the presence of a fixed amount of sodium dodecyl sulfate (SDS) or lithium perfluorooctyl sulfonate (LiFOS) is investigated. In all systems studied, surfactants and telechelic polymers form mixed aggregates. Their aggregation numbers are reduced and evolve with the concentration of each component. For example, with SDS at 8 mM, the mixed aggregates are composed of 1 AP and 15 SDS or 9 APs and 45 SDS molecules for 1 or 3 wt % of polymer, respectively. The addition of a surfactant enhances the number density of aggregates, which causes the increase of the gel viscosity.

During pendant drop experiments, a model physical gel made from oil in water microemulsion droplets reversibly linked together by triblock copolymers, exhibit a very peculiar filament rupture corresponding to highly brittle failure of a viscoelastic fluid. The fracture propagation has been tracked by high speed videomicroscopy. Analysis of the time evolution of the fracture profile shows that the fracture is purely elastic and reversible without any significant bulk and interfacial viscous dissipation. However, since the elastic moduli of such complex fluids are low, hyper elastic corrections have to be taken into account for a quantitative analysis of the fracture profile. This brittle behavior is well explained by a hyperelastic generalization of the viscoelastic trumpet model of de Gennes. The velocity of the fracture’s propagation is measured and compared to the predictions of a simple microscopic model.

We report on a small angle neutron scattering (SANS) study of self-organization of a novel triblock copolymer containing a crystalline poly(ethylene terephthalate) oligomer, a rubbery poly(lauryl acrylate) midblock, and a polyelectrolyte block (quaternized poly(2-(dimethylamino)ethyl methacrylate)) of various length. The rheology of the solutions showed a transition from Newtonian flow at low concentrations, to shear-thinning at intermediate concentrations, and finally a yield behavior at high concentrations. The microstructure of the samples investigated by SANS was found to evolve strongly with the polyelectrolyte block length. The data were analyzed in terms of aggregation numbers, radius of gyration, and aggregate hydration. Complete modeling of the intensity curves was achieved by an inversion method extracting an average aggregate radial volume fraction profile. In both rheology and microstructure, a surprising strong impact of the small PET block was observed.