Magnetic wire as stress controlled micro-rheometer for cytoplasm viscosity measurements

We review here different methods to measure the bulk viscosity of complex fluids using micron-sized magnetic wires. The wires are characterized by length of a few microns and diameter of a few hundreds of nanometers. We first draw analogies between cone-and-plate rheometry and wire-based microrheology. In particular we highlight that magnetic wires can be operated as stress-controlled rheometers for two types of testing, the creep-recovery and steady shear experiments. In the context of biophysical applications, the cytoplasm of different cell lines including fibroblasts, epithelial and tumor cells is studied. It reveals that the interior of living cells can be described as a viscoelastic liquid with a static viscosity comprised between 10 and 100 Pas. We extend the previous approaches and show that the proposed technique can also provide time resolved viscosity data, which for cells display strong temporal fluctuations. The present work demonstrates the high potential of the magnetic wires for quantitative rheometry in confined espaces.Comment: 11 pages, 6 figures, 40 reference

Shear-induced transitions and instabilities in surfactant wormlike micelles

In this review, we report recent developments on the shear-induced transitions and instabilities found in surfactant wormlike micelles. The survey focuses on the non-linear shear rheology and covers a broad range of surfactant concentrations, from the dilute to the liquid-crystalline states and including the semi-dilute and concentrated regimes. Based on a systematic analysis of many surfactant systems, the present approach aims to identify the essential features of the transitions. It is suggested that these features define classes of behaviors. The review describes three types of transitions and/or instabilities : the shear-thickening found in the dilute regime, the shear-banding which is linked in some systems to the isotropic-to-nematic transition, and the flow-aligning and tumbling instabilities characteristic of nematic structures. In these three classes of behaviors, the shear-induced transitions are the result of a coupling between the internal structure of the fluid and the flow, resulting in a new mesoscopic organization under shear. This survey finally highlights the potential use of wormlike micelles as model systems for complex fluids and for applications.Comment: 64 pages, 31 figures, 2 table

Superstructures par agr\'egation contr\^ol\'ee de nanocollo\"ides: caract\'erisation structurale par diffusion de neutrons aux petits angles et simulation num\'erique

The complexation of micelles or charged nanoparticles with neutral-charged block copolymers in aqueous solutions leads to the formation of colloidal superstructures also termed 'colloidal complexes'. Their primary interest relies in their monodispersity in size, and in their increased domain of stability. In this review, the structural characterization by dynamic light scattering, cryo-TEM, and small angle neutron scattering is presented. Small angle neutron scattering results have been analyzed using numerical simulations - Monte Carlo or reverse Monte Carlo (RMC). Such simulations are useful to show the compatibility between different models of colloidal superstructures, and experiment. Our results have allowed us to propose a generic structure of complex colloids, made of a dense core of interacting colloids, bridged by polyelectrolyte blocks, and a hydrated corona. We have shown that such superstructures are formed systematically in these systems, with either micelles or nanoparticles, for different copolymers, and different charges. The text is in French

Mono- versus Multi-phosphonic Acid Based PEGylated Polymers for Functionalization and Stabilization of Metal (Ce, Fe, Ti, Al) Oxide Nanoparticles in Biological Media

International audienceFor applications in nanomedicine, particles need to be functionalized to prevent protein corona formation and/or aggregation. Most advanced strategies take advantage of functional polymers and assembly techniques. Nowadays there is an urgent need for coatings that are tailored according to a broad range of surfaces and that can be produced on a large scale. Herein, we synthesize mono-and multi-phosphonic acid based poly(ethylene glycol) (PEG) polymers with the objective of producing efficient coats for metal oxide nanoparticles. Cerium, iron, titanium and aluminum oxide nanoparticles of different morphologies (spheres, platelets, nanoclusters) and sizes ranging from 7 to 40 nm are studied in physiological and in protein rich cell culture media. It is found that the particles coated with mono-functionalized polymers exhibit a mitigated stability over time ( months). With the latter, PEG densities in the range 0.2-0.5 nm-2 and layer thickness about 10 nm provide excellent performances. The study suggests that the proposed coating allows controlling nanomaterial interfa-cial properties in biological environments

Stability and Adsorption Properties of Electrostatic Complexes : Design of Hybrid Nanostructures for Coating Applications

We report the presence of a correlation between the bulk and interfacial properties of electrostatic coacervate complexes. Complexes were obtained by co-assembly between cationic-neutral diblocks and oppositely charged surfactant micelles or 7 nm cerium oxide nanoparticles. Light scattering and reflectometry measurements revealed that the hybrid nanoparticle aggregates were more stable both through dilution and rinsing (from either a polystyrene or a silica surfaces) than their surfactant counterparts. These findings were attributed to a marked difference in critical association concentration between the two systems and to the frozen state of the hybrid structures.Comment: 3 pages, 3 figures, 27 references, to appear in Langmuir Letter

Elaboration of superparamagnetic nanorods using iron oxide nanoparticles and polymers.

International audienceIn this presentation, we give an account of the formation of colloidal and supracolloidal aggregates obtained by controlled co-assembly of 7 nm particles with copolymers