The new very small angle neutron scattering spectrometer at Laboratoire Leon Brillouin

The design and characteristics of the new very small angle neutron scattering spectrometer under construction at the Laboratoire Leon Brillouin is described. Its goal is to extend the range of scattering vectors magnitudes towards 2x10{-4} /A. The unique feature of this new spectrometer is a high resolution two dimensional image plate detector sensitive to neutrons. The wavelength selection is achieved by a double reflection supermirror monochromator and the collimator uses a novel multibeam design

A double supermirror monochromator for neutron instrumentation at LLB

The design and characteristics of a double supermirror monochromator for neutron instrumentation at the Laboratoire Leon Brillouin is described. The aim of this monochromator is to reduce the intense gamma-radiation produced by conventional velocity selectors and to avoid a direct view of the guide while keeping a comparable neutron transmission (higher than 70%). The monochromator offers a continuous choice of wavelength selection in the range 0.5 to 2 nm

A study of flux lines lattice order and critical current with time of flight small angle neutron scattering

Small angle neutron scattering (SANS) is an historical technique to study the flux lines lattice (FLL) in a superconductor. Structural characteristics of the FLL can be revealed, providing fundamental information for the physics of vortex lattice. However, the spatial resolution is limited and all the correlation lengths of order are difficult to extract with precision. We show here that a time of flight technique reveals the Bragg peak of the FLL, and also its translational order with a better resolution. We discuss the implication of these results for pinning mechanisms in a Niobium sample.Comment: accepted in PR

Why pinning by surface irregularities can explain the peak effect in transport properties and neutron diffraction results in NbSe2 and Bi-2212 crystals?

The existence of a peak effect in transport properties (a maximum of the critical current as function of magnetic field) is a well-known but still intriguing feature of type II superconductors such as NbSe2 and Bi-2212. Using a model of pinning by surface irregularities in anisotropic superconductors, we have developed a calculation of the critical current which allows estimating quantitatively the critical current in both the high critical current phase and in the low critical current phase. The only adjustable parameter of this model is the angle of the vortices at the surface. The agreement between the measurements and the model is really very impressive. In this framework, the anomalous dynamical properties close to the peak effect is due to co-existence of two different vortex states with different critical currents. Recent neutron diffraction data in NbSe2 crystals in presence of transport current support this point of view

Deformation plastique d'un polymere semi-cristallin (le polypropylene isotactique) : etude par diffusion de neutrons aux petits angles de la conformation des chaines

CNRS TD Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

pH-sensitive micellar systems for controlled drug delivery: synthesis and structural characterization by small-angle neutron scattering

The aim of the project is the preparation of micellar nanocarriers made of biocompatibles copolymers and their structural analysis by Small Angle Neutron Scattering (SANS). These micelles could be used in drug delivery applications to fight cancer1. The hydrophobic polycaprolactone (PCL) core is intended to incorporate the drug. The corona of hydrophilic polyethylene oxide (PEO) stabilizes the nanocarriers with respect to the plasma proteins. The pH in the neighborhood of the tumoral cells is lower than in the healthy cells. We incorporated a pH-sensitive sequence of poly(2-vinylpyridine) (P2VP). As a result, these micelles are expected to deliver their drug near the cancerous cells without affecting the healthy cells. When the pH is acidic, the P2VP is protonated and the chains are repulsive. The micellar size is then larger than in basic pH, when the P2VP is precipitated on the PCL core. We prepared PCL65-b-P2VP31 / PCL65-b-PEO114 and PCL32-b-P2VP52 / PCL36-b-PEO114 50:50 mixtures of diblocks copolymers. The resulting mixed micelles are analyzed by SANS. We developed a theoretical model with a spherical water-free PCL core. The PEO corona is described as consisting of gaussian chains with a thickness estimated as twice the chain gyration radius, Rg. We propose two alternatives for handling the P2VP zone. The P2VP molecules are either assumed to be Gaussian chains or they fill a shell of thickness L with possible water penetration.The fitting of the models to the experimental scattering cross sections leads to important structural parameters like the aggregation number, the core radius, the gyration radius and the thickness of the P2VP shell

Polymerization induced Self-Assembly toward a new breakthrough for formulation of nanocarriers based on polysaccharide derivatives

International audienc

Lamellar Bilayer to Fibril Structure Transformation of Tough Photonic Hydrogel under Elongation

Synthetic hydrogels possessing both macroscopic anisotropic structure and toughness, which are analogous to the load-bearing bio-tissues such as muscles and tendons, are rarely available. Studying the molecular mechanism of tough and anisotropic hydrogel under deformation is beneficial to understand the load-deformation functions of soft bio-tissues. In this work, the deformation-induced structure transformation of a macroscopically anisotropic and tough hydrogel has been investigated to understand the role of structure evolution for enhanced toughness. At rest, the hydrogel possesses a well-defined hierarchical structure in which self-assembled nanometer thick lamellar bilayers are alternatively stacked in hundred nanometer thick hydrogel matrixes. Stretching along the lamellar direction induces structure transformation from lamellar bilayers to hierarchical fibrous structures aligned along the deformation axis. The generated hierarchical structures consist of micrometer thick fiber bundles made from nanometer thick fibrils analogous to tropo-collagen bundles or microfibrils of the tendon. The fibrous structure formed at large elongation is associated with damage and rupture of the bilayers, which underpins the molecular mechanism of the unique mechanical behaviors of the tough lamellar hydrogel