We report on a small angle neutron scattering (SANS) study of self-organization of a novel triblock copolymer containing a crystalline poly(ethylene terephthalate) oligomer, a rubbery poly(lauryl acrylate) midblock, and a polyelectrolyte block (quaternized poly(2-(dimethylamino)ethyl methacrylate)) of various length. The rheology of the solutions showed a transition from Newtonian flow at low concentrations, to shear-thinning at intermediate concentrations, and finally a yield behavior at high concentrations. The microstructure of the samples investigated by SANS was found to evolve strongly with the polyelectrolyte block length. The data were analyzed in terms of aggregation numbers, radius of gyration, and aggregate hydration. Complete modeling of the intensity curves was achieved by an inversion method extracting an average aggregate radial volume fraction profile. In both rheology and microstructure, a surprising strong impact of the small PET block was observed.

This paper reports on the polyion complex micelles (PIC micelles) formed between neutral-ionizable double hydrophilic block copolymers (DHBC), poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA), and oligochitosan, a natural polyamine. The controlled synthesis of PEO-b-PAA polymers was achieved by atom transfer radical polymerization (ATRP) of tert-butyl acrylate with omega-bromide-functionalized PEO macroinitiators (M-w = 2000 and 5000 g mol(-1)) and the subsequent deprotection reaction under acidic conditions. A series of copolymers with a narrow molecular weight distribution (M-w/M-n <= 1.2) and varied PAA block lengths was synthesized. Capillary electrophoresis (CE) was shown to unambiguously prove the blocky structure of the copolymers. It also showed that about 60% of the sodium counter ions were condensed onto the polyacrylate block in the pure diblock copolymer solution, which is consistent with the formation of polyion complex micelles triggered by counter-ion release in the presence of oligochitosan. The formation of oligochitosan/PAA-PEO core-corona micelles has been investigated by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). A minimum length of the PAA block is necessary to ensure micelle formation. The range of pH, where PIC micelles form, critically depends on the PAA block length, which also determines the size of the micelles. Micelles can be dissociated at ionic strength above 0.4 mol L-1. Since these PIC micelles have been used as recyclable structuring agents for the formation of ordered mesoporous materials, the reversibilty of the assembling process was studied upon pH and ionic strength cyclic variations. A hysteresis of stability was observed at low pH, probably due to hydrogen bonding.

We introduce a model describing failure in transient networks. The two main ingredients are (i) the lifetime of a non connecting bond is far smaller than that of an active bond, (ii) the lifetime of an active bond is a decreasing function of the force carried by this bond. We show that these assumptions are sufficient to predict a failure threshold. Below this threshold the bonds distribution is driven by a diffusion equation. The bonds are redistributed homogeneously in the sample, leading to its self-adhesive feature. Beyond this threshold, the diffusion coefficient is negative, causing a catastrophic amplification of any heterogeneity. The final stage is the fracture. Finally, we give an interpretation of delayed fractures for these kinds of materials.

Liquid crystal ordering is an opportunity to develop novel materials and applications with carbon nanotubes spontaneously aligned on macroscopic scales. Nevertheless, achievement of large orientational order parameter and extended monodomains remains challenging. In this work, we show that shortening nanotubes allows the formation of liquid crystals that can easily be oriented under the form of large macroscopic monodomains. The orientational order parameter of single-wall nanotube liquid crystals measured by polarized Raman spectroscopy at the isotropic-nematic transition exceeds by far the value reported in previous experiments. The presently measured order parameter approaches the value theoretically expected for liquid crystals made of rigid rods in solution. This finding suggests that the production of highly ordered nanotubebased liquid crystals was presumably limited in earlier contributions by the length and waviness of long nanotubes. Both factors increase the material viscosity, can yield some elasticity, and stabilize topological defects.

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

We report a demonstration video-rate heterodyne holography in off-axis configuration. Reconstruction and display of 1 Megapixel holograms is achieved at 24 frames per second, with a graphics processing unit. Our claims are validated with real-time screening of steady-state vibration amplitudes in a wide-field, non-contact vibrometry experiment.