Reusable and recyclable quartz crystal microbalance sensors

In this communication, we report a simple procedure to recycle quartz crystal microbalance sensors. In particular we show that a sacrificial functional PS thin film deposited on top of silica (or gold) sensor does not influence the features and reproducibility of the benchmarked PSS/PDADMAC polyelectrolyte multilayer growth. A simple rinsing of the assembly with toluene at the end of a given experiment enables the reusing of the same sensor for tenths of times or more providing a neat economical and ecological gain; an approach that hopefully will spread out.Analyse Ultra-sensible Bas-coût par Assemblage Intégré de micro-Nano objEtsAssemblage Macromoléculaire Hors-équilibre Compréhension, Contrôle & nouvelles structure

Fine-tuning the assembly of highly stable oppositely charged ceriumoxide nanoparticles in solution and at interfacesSribharani

tIn this work we have shown how to fine-tune the electrostatic assembly of oppositely charged ceriumoxide nanoparticles (NPs) in a solution and at a solid/liquid interface. In a first stage, we have developedanionic and cationic CeO2NPs stable in a highly saline environment and a wide pH range via efficientelectro-steric interactions. Anionic NPs were obtained by coating bare NPs with short polyacrylic acid(PAA) chains through a Precipitation-Redispersion method. Whereas cationic NPs were formulated bytethering branched polyethyleneimine (bPEI) chains onto PAA-coated ceria NPs through the formation ofamide bonds with the help of imide cross-linkers. The covalent attachment of bPEI chains was evidenced through NMR characterizations while thermogravimetric (TGA), dynamic light scattering (DLS) and zetapotential measurements confirmed the successful encapsulation by both types of weak polyelectrolytes.In a second stage, the high stability of both NP dispersions toward high ionic strength (up to 4 M NH4Cl)enabled to generate hybrid clusters in a controlled way by fine tuning their co-assembly following adesalting transition route monitored by DLS. In a last part, we have extended our approach to surfaces andgenerated all-nanoparticle layer grown directly from a liquid/solid interface monitored by Quartz CrystalMicrobalance (QCM)...

Direct experimental evidences of the density variation of ultrathin polymer films with thickness

International audienceBeyond the peculiar glass transition temperature (Tg) studied extensively for over two decades, we have investigated in this work the variation of the mass density of polymer thin films, a key property barely put forward in the literature. We were able to directly measure the mass density of polystyrene (PS) and poly (methyl methacrylate) (PMMA) thin films as a function of their thickness from accurate Quartz Crystal Microbalance (QCM) dissolution experiments. Depending on the chemical nature of the polymers, the results showed an unambiguous variation of the mass density when the film thickness was reduced: an increase for PS and a decrease for PMMA films. In the last part, we measured the coefficient of thermal expansion (CTE) of both polymers to rationalize the apparent inconsistency of an increase/decrease in the mass density with the commonly observed depression/rise of the Tg of PS/PMMA films. Surprisingly, the coefficient of thermal expansion and the mass density showed a similar variation with thickness, pointing out a clear correlation between the glass transition temperature, the coefficient of thermal expansion and the free volume of the polymer

Gelling of Oil-in-Water Emulsions Comprising Crystallized Droplets

We fabricate oil-in-water emulsions above the melting temperature of the oil phase (hexadecane and/or paraffin). Upon cooling, the oil droplets crystallize and the initially fluid emulsions turn into hard gels. The systems evolve by following two distinct regimes that depend on the average droplet size and on the oil nature. In some cases gelling involves partial coalescence of the droplets, i.e., film rupturing with no further shape relaxation because of the solid nature of the droplets. In some other cases, gelling occurs without film rupturing and is reminiscent of a jamming transition induced by surface roughness. We prepare blends of oils having different melting temperatures, and we show that it is possible to reinforce the gel stiffness by applying a temperature cycle that produces partial melting of the crystal mass, followed by recrystallization

Freeze-Fracture TEM Imaging of Robust Order in Swollen Phases of Amphiphilic Diblock Copolymers

We report on the structures exhibited by two different diblock poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) copolymers in water, a selective solvent. Using a combination of X-ray scattering and freeze fracture-transmissionelectron microscopy (FF-TEM), we show that these structures can be widely swollen while retaining their initial morphology and a high degree of long-range order. The analysis of the FF-TEM pictures also evidences the presence of water crystallites of regular size and shape within the confined water domains. We relate the growth of these crystallites to the high local ionic strength of the water swelling the PAA brushes. Moreover, the confinement of the crystallites growth shows that the swollen phases have a very robust structure, potentially useful for confining colloidal particle

Dislocation-loop-mediated smectic melting

We report the direct observation, using freeze-fracture transmission electron microscopy, of topological melting in a lyotropic system in the vicinity of a smectic-cholesteric (N*) phase transition. The proliferation of dislocations leads to at least one, and possibly two intermediate phases, characterised by orientational ordering of the dislocation loops and the subsequent unbinding of the screw-dislocation lines. PAC