Structured solvent effects on precipitation

Structured ternary fluids as nanocrystal incubators for enhanced crystallization control

Crystallization in structured ternary fluids can proceed via higher nucleation rate and slower crystal growth pathways that are impossible to access in normal unstructured solutions. Hence, structured ternary fluids can act as nanocrystal incubators.

OSTE+ for in situ SAXS analysis with droplet microfluidic devices

In recent years, microfluidic-based sample preparation techniques have emerged as a powerful tool for measurements at large scale X-ray facilities. Most often the microfluidic device was a form of hybrid system, i.e. an assembly of different materials, because a simple, versatile and inexpensive microfabrication method, on the one hand, and X-ray compatibility, on the other hand, cannot generally be achieved by the same material. The arrival of a new polymer family based on off-stoichiometric thiol-ene-epoxy (OSTE+) has recently redistributed the cards. In this context, we studied the relevance and the compatibility of OSTE+ for small-angle X-ray scattering (SAXS) studies. The material was characterized regarding its X-ray properties (transmission coefficient, attenuation coefficient, scattering pattern and polymer aging under X-ray light) and their comparison with those of the usual polymers used in microfluidics and/or for synchrotron radiation experiments. We show that OSTE+ has a better SAXS signal than polyimide, the polymer of reference in the SAXS community. Then a detailed protocol to manufacture a suitably thin full OSTE+ chip (total thickness <500 μm) is described and the potency of full OSTE+ devices for in situ SAXS studies is highlighted in two case-studies: the characterization of gold nanoparticles and the precipitation of cerium oxalate particles, both in moving droplets. Additionally, a method to analyze the scattering signals from droplet and carrier phase in a segmented flow is proposed.

Cerium Oxalate Morphotypes: Synthesis and Conversion into Nanocrystalline Oxide

Cerium dioxide is a scientifically and technologically important material with a wide range of potential applications, particularly in solid oxide fuel cells and catalysis. Herein, we report a study focusing on the synthesis of nanocrystalline cerium dioxide via thermal decomposition of the oxalate salt. Simply by changing reaction conditions (temperature, concentration, acidity, strike) during the precipitation of the cerium solution with oxalic acid, we were able to obtain different morphologies. The main reaction parameters were mapped and linked to the morphology of the final products. Additionally, it was proved that oxalate precipitation is a robust reaction proceeding at relatively extreme contitions. Moreover, the conversion of cerium oxalate to nanocrystalline oxide was followed to monitor the progress of the reaction, the texture evolution, and the grain growth. The results showed that, for unvaried heating cycle, the grain size of converted material is linked to morphology. The thinner was the original microcrystal the smaller were the CeO₂ nanocrystals after calcination. In addition, the grains were found smaller near the edges of the ex-oxalate microcrystals. In both cases, this behavior results from asymmetrical limitations of diffusion during grain growth.

Nanometric Surface Oscillation Spectroscopy of Water-Poor Microemulsions

Selectively exchanging metal complexes between emulsified water-poor microemulsions and concentrated solutions of mixed electrolytes is the core technology for strategic metal recycling. Nanostructuration triggered by solutes present in the organic phase is understood, but little is known about fluctuations of the microemulsion-water interface. We use here a modified version of an optoelectric device initially designed for air bubbles, in order to evidence resonant electrically induced surface waves of an oily droplet suspended in an aqueous phase. Resonant waves of nanometer amplitude of a millimeter-sized microemulsion droplet containing a common ion-specific extractant diluted by dodecane and suspended in a solution of rare earth nitrate are evidenced for the first time with low excitation fields (5 V/cm). From variation of the surface wave spectrum with rare earth concentration, we evidence uptake of rare-earth ions at the interface and at higher concentration the formation of a thin "crust" of liquid crystal forming at unusually low concentration, indicative of a surface induced phase transition. The effect of the liquid crystal structure on the resonance spectrum is backed up by a model, which is used to estimate crust thickness.