Philippe Boltenhagen

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We observe a shear-flow-induced phase transition in wormlike micelle solutions which depends on whether the applied stress or the applied shear rate is held constant. When the shear stress is held constant, the system macroscopically phase separates into two coexisting phases with a single stable interface between them. By contrast, when the shear rate is(More)
We report the first direct observation of shear-induced structures in low concentration wormlike micellar solutions. The structures consist of micron-sized patches which are much larger than individual equilibrium micelles and occupy 5%–10% of the fracture area. Such morphologies are consistent with recent reports of increased light scattering under shear(More)
– The time evolution of flow-induced structures in low-concentration worm-like micellar solutions is studied using direct visualization and rheological methods. The visualization measurements show growth of a new viscous shear-induced phase (SIP) starting on the inner wall of a Couette shear cell at a time t1 after the commencement of shear flow. The SIP(More)
Upon drying, colloidal suspensions undergo a phase transformation from a "liquid" to a "gel" state. With further solvent evaporation, tensile stresses develop in the gel, which ultimately leads to fractures. These generally manifest themselves in regular cracking patterns which reflect the physical conditions of the drying process. Here we show(More)
We investigate, at a laboratory scale, the collapse of cylindrical shells of radius R and thickness t induced by a granular discharge. We measure the critical filling height for which the structure fails upon discharge. We observe that the silos sustain filling heights significantly above an estimation obtained by coupling standard shell-buckling and(More)
Freeze-fractured specimens of the L,, pha~e of a swollen quasi-ternary surfactant (cetylpyridinium chloride/hexanol/btine), have been observed by electron microscopy. The textures show the same features as those oberved by optical microscopy, viz. defects with negative Gaussian curvature (focal conic domains of the usual type) close to the phase boundary(More)
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