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.

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 new class of self−assembled transient networks made of surfactant micelles of tunable morphology (from spheres, to rodlike to wormlike) reversibly linked by telechelic polymers. Linear rheological measurements show that three distinct domains can be defined depending on the morphologies of the micelles: a domain where the micelles are isolated and not entangled, an intermediate domain where the micelles are partially entangled and a domain where the micelles are fully entangled. Flow curves of the transient networks of tunable morphology associated with structural informationjs obtained from Rheo−SAXS suggest that one can associate to the three domains distinct failures modes: a brittle mode, an intermediate mode and finally a ductile/shear banding mode, as the micelles grow. The ultimate goal is to elucidate the parameters that drive the transition

The strong associative behaviour between cholesterol-modified dextran (CMD) and short and long polyoxyethylene cholesteryl ether (ChEO10) micelles were investigated using rheology and small-angle neutron scattering (SANS). In solutions of short rod-like micelles (ChEO10 alone), the addition of 5.0 wt% CMD induced a remarkable transition from a Newtonian system to a highly solid-like viscoelastic network, with an increase in zero-shear viscosity of over 5 orders of magnitude. The frequency sweeps at ChEO10 concentrations above 2.5 wt% were fitted to a Maxwell model with 3 elements and, quite remarkably, fell onto a single master curve, while no network was formed at 2.5 wt% micelles. Viscoelastic solutions of wormlike micelles (WLMs) were obtained by adding the co-surfactant triethylene glycol monododecyl ether (C12EO3) to ChEO10 solutions at a constant ChEO10/C12EO3 ratio of 5/1. The introduction of CMD into the WLM solutions induced a transition to a more liquid-like behaviour (G″/G′ increased), however both moduli increased by one order of magnitude. At the lowest ChEO10 concentration (2.5%), the solid-like behaviour was lost. Overall, a comparable rheological response was obtained for the WLM and the short rods with CMD, however the WLM/CMD behaviour suggested a wider spectrum of relaxation processes, longer relaxation times and higher plateau moduli. SANS data from the polymer/micelles mixtures displayed a strong structural peak and were remarkably identical for both ChEO10/CMD and ChEO10/C12EO3/CMD systems, suggesting a very similar type of network structure, independently of the initial size of the micelles. Overall, all the results taken together show a very high affinity between the polymer and the micelles and suggest a breakup of the WLM induced by CMD. The resulting network is constituted by polymeric chains connected by micellar aggregates through hydrophobic interactions between the micellar cholesterol cores and the pendent cholesterol moieties of the polymer

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