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Grelet E.,CNRS Paul Pascal Research Center
Physical Review X | Year: 2014

We report on the phase behavior of a model system of colloidal rodlike particles, namely, the filamentous fd viruses, in the dense liquid crystalline states. After determining the phase boundaries as a function of the added salt, we propose a renormalization of the phase diagram accounting for the screened electrostatic repulsions between the particles through an effective hard-rod diameter. Including explicitly counterion condensation, we show that our heuristic model captures the main feature of the nematic-to-smectic phase transition of long hard rods, i.e., its universal packing fraction. The importance of rod flexibility on the relative stability of the different concentrated mesophases is also demonstrated, evidencing, in particular, the existence of a smectic-B phase in between the smectic-A and the columnar phases.

Divoux T.,CNRS Paul Pascal Research Center | Fardin M.A.,University Paris Diderot | Manneville S.,CNRS Physics Laboratory | Lerouge S.,University Paris Diderot
Annual Review of Fluid Mechanics | Year: 2016

Even in simple geometries, many complex fluids display nontrivial flow fields, with regions where shear is concentrated. The possibility for such shear banding has been known for several decades, but in recent years, we have seen an upsurge in studies offering an ever-more precise understanding of the phenomenon. The development of new techniques to probe the flow on multiple scales with increasing spatial and temporal resolution has opened the possibility for a synthesis of the many phenomena that could only have been thought of separately before. In this review, we bring together recent research on shear banding in polymeric and soft glassy materials and highlight their similarities and disparities. © Copyright 2016 by Annual Reviews. All rights reserved.

Schmitt V.,CNRS Paul Pascal Research Center | Ravaine V.,CNRS Institute of Molecular Sciences
Current Opinion in Colloid and Interface Science | Year: 2013

Colloidal gel particles called microgels have shown their ability to adsorb at an oil-water interface and stabilise emulsion named Pickering emulsions. Such particles are soft, deformable, and porous, and they can swell or contract under the action of an external stimulus. These specificities make them emulsifiers of special interest as they offer a large versatility to emulsions and materials elaborated thereof. This modularity is in counterpart at the origin of an abundant and often contradictory literature. The aim of this paper is to review recent advances in the emulsion stabilisation mechanism, particularly focusing on the microgel conformation at the interface in relation with the mechanical interface behaviour and the emulsion macroscopic stability. A sum up of the unambiguous knowledge is also proposed as well as few central questions that remain to be answered to in the domain. © 2013 Elsevier Ltd.

Gao F.,CNRS Paul Pascal Research Center
Nature communications | Year: 2010

Poor electron transfer and slow mass transport of substrates are significant rate-limiting steps in electrochemical systems. It is especially true in biological media, in which the concentrations and diffusion coefficients of substrates are low, hindering the development of power systems for miniaturized biomedical devices. In this study, we show that the newly engineered porous microwires comprised of assembled and oriented carbon nanotubes (CNTs) overcome the limitations of small dimensions and large specific surface area. Their improved performances are shown by comparing the electroreduction of oxygen to water in saline buffer on carbon and CNT fibres. Under air, and after several hours of operation, we show that CNT microwires exhibit more than tenfold higher performances than conventional carbon fibres. Consequently, under physiological conditions, the maximum power density of a miniature membraneless glucose/oxygen CNT biofuel cell exceeds by far the power density obtained for the current state of art carbon fibre biofuel cells.

Drummond C.,CNRS Paul Pascal Research Center
Physical Review Letters | Year: 2012

Friction is always present when surfaces in contact are set in motion. In this work I describe how a precise, active control of the global friction is possible by adjusting the local molecular conformation of a polyelectrolyte coating via the application of an alternating electric field. The intensity of the applied field determines the degree of interpenetration between polymer brushes in contact, regulating chain stretching while sliding, which is the process at the origin of the global friction. The dynamics of the problem is controlled by the relaxation times of the polyelectrolyte. © 2012 American Physical Society.

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