Synthesis and Characterization of Temperature-Responsive N-Cyanomethylacrylamide-Containing Diblock Copolymer Assemblies in Water

We have previously demonstrated that poly(N-cyanomethylacrylamide) (PCMAm) exhibits a typical upper-critical solution temperature (UCST)-type transition, as long as the molar mass of the polymer is limited, which was made possible through the use of reversible addition-fragmentation chain transfer (RAFT) radical polymerization. In this research article, we use for the first time N-cyanomethylacrylamide (CMAm) in a typical aqueous dispersion polymerization conducted in the presence of poly(N,N-dimethylacrylamide) (PDMAm) macroRAFT agents. After assessing that well-defined PDMAm-b-PCMAm diblock copolymers were formed through this aqueous synthesis pathway, we characterized in depth the colloidal stability, morphology and temperature-responsiveness of the dispersions, notably using cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and turbidimetry. The combined analyses revealed that stable nanometric spheres, worms and vesicles could be prepared when the PDMAm block was sufficiently long. Concerning the thermoresponsiveness, only diblocks with a PCMAm block of a low degree of polymerization (DPn,PCMAm < 100) exhibited a UCST-type dissolution upon heating at low concentration. In contrast, for higher DPn,PCMAm, the diblock copolymer nano-objects did not disassemble. At sufficiently high temperatures, they rather exhibited a temperature-induced secondary aggregation of primary particles. In summary, we demonstrated that various morphologies of nano-objects could be obtained via a typical polymerization-induced self-assembly (PISA) process using PCMAm as the hydrophobic block. We believe that the development of this aqueous synthesis pathway of novel PCMAm-based thermoresponsive polymers will pave the way towards various applications, notably as thermoresponsive coatings and in the biomedical field.

Multi-Step Crystallization and Chemical Evolution of Sodium Yttrium Fluoride

Two-step crystallization mechanisms based on spinodal decomposition followed by nucleation are commonly observed both in the laboratory and in nature. While this pathway may require chemical reactions, subsequent nucleation and growth are often considered as separate, discrete events from the reaction itself. Recent work has also shown a distinct intermediate step involving the formation of an amorphous aggregate. Here we report a novel four-step mechanism in the aqueous synthesis of sodium yttrium fluoride involving 1) the segregation of aqueous ions into a dense liquid phase, 2) the formation of an amorphous aggregate, 3) nucleation of a cubic YF3 phase, and 4) subsequent solid-state diffusion of sodium and fluoride ions to form a final NaYF4 phase. The final step involves a continuous, gradual change of the solid phase’s chemical stoichiometry from YF3 toward NaYF4. Unlike previously studied nucleation and growth mechanisms, the stoichiometry of the final solid phase evolves throughout the crystallization process rather than being determined at nucleation. This novel four-step mechanism provides a new perspective into the nucleation and growth of many other crystalline materials given the ubiquity of nonstoichiometric compounds in nature.

Synthesis and Characterization of Novel Nanoparticles of Lithium Aluminum Iodate LiAl(IO3)4, and DFT Calculations of the Crystal Structure and Physical Properties

Here we report on the non-hydrothermal aqueous synthesis and characterization of nanocrystalline lithium aluminum iodate, LiAl(IO3)4. Morphological and compositional analyses were carried out by using scanning electron microscopy (SEM) and energy-dispersive X-ray measurements (EDX). The optical and vibrational properties of LiAl(IO3)4 have been studied by UV-Vis and IR spectroscopy. LiAl(IO3)4 is found to crystallize in the non-centrosymmetric, monoclinic P21 space group, contrary to what was reported previously. Theoretical simulations and Rietveld refinements of crystal structure support this finding, together with the relatively high Second Harmonic Generation (SGH) response that was observed. Electronic band structure calculations show that LiAl(IO3)4 crystal has an indirect band gap Egap=3.68 eV, in agreement with the experimental optical band gap Egap=3.433 eV. The complex relative permittivity and the refraction index of LiAl(IO3)4 have also been calculated as a function of energy, as well as its elastic constants and mechanical parameters. LiAl(IO3)4 is found to be a very compressible and ductile material. Our findings imply that LiAl(IO3)4 is a promising material for optoelectronic and non -linear optical applications.

A mild aqueous synthesis of ligand-free copper nanoparticles for low temperature sintering nanopastes with nickel salt assistance

An organic ligand-free aqueous-phase synthesis of copper (Cu) nanoparticles (NPs) under an air atmosphere was successfully achieved by reducing copper(II) oxide particles with a leaf-like shape in the presence of Ni salts at room temperature. The resulting Cu NPs with a mean particle diameter of ca. 150 nm exhibited low-temperature sintering properties due to their polycrystalline internal structure and ligand-free surface. These Cu NPs were applied to obtain Cu NP-based nanopastes with low-temperature sintering properties, and the resistivities of the obtained Cu electrodes after annealing at 150 °C and 200 °C for 30 min were 64 μΩ∙cm and 27 μΩ∙cm, respectively. The bonding strength between oxygen-free Cu plates prepared using the Cu NP-based nanopastes reached 32 MPa after pressure-less sintering at 260 °C for 30 min under a nitrogen atmosphere. The developed manufacturing processes using the developed Cu nanopastes could provide sustainable and low-CO2-emission approaches to obtain Cu electrodes on flexible films and high-strength bonding between metal plates as die-attach materials for power devices under energy- and resource-saving conditions.

Synthesis and Characterisation of Photocatalyst Silver/Silver Halide Nanocomposites

<p>The photochemical activity of silver halides forms the basis of photography and latent image formation. More recently it has been used to create hybrid silver/silver halide nanoparticles. These are formed through partial reduction of Ag⁺ to Ag⁰ by a photochemical self-sensitisation when irradiated with light. This gives the silver/silver halide nanoparticles interesting photocatalytic properties. As such, these silver/silver halide nanoparticles have seen to be part of group of photocatalysts known as plasmonic photocatalysts. Where, the photocatalytic mechanism is enhanced by the surface plasmon resonance of noble metal nanodomains on the surface of the silver halide nanoparticle. The silver/silver halide nanoparticles of Cl⁻, Br⁻ and I⁻ were synthesised and characterised. Silver/silver halide nanoparticles were then incorporated into porous support materials creating silver/silver halide nanocomposite materials. This was through a straight forward aqueous synthesis method, where silver halide nanoparticles precipitated from solution, and nanoparticle size, shape and stabilisation was controlled by the porous support material. Silver/silver halide nanocomposite samples using Cl⁻, Br⁻ and I⁻ were synthesised using wool fibres, kraft paper fibres and nanostructured calcium silicate as supports. UV/Vis and XRD showed Ag⁰ nanodomains were formed during the self-sensitisation process. SEM showed the morphology of the nanocomposites and that the nanoparticles were distributed within the nanocomposite matrix, not deposited on the surface. Preliminary photocatalytic activity of Ag/AgCl nanoparticles and nanocomposites was evaluated through the degradation of methylene blue when irradiated with light. All samples showed increased photocatalytic activity with the Ag/AgCl nanoparticles.</p>

Synthesis and Characterisation of Photocatalyst Silver/Silver Halide Nanocomposites

<p>The photochemical activity of silver halides forms the basis of photography and latent image formation. More recently it has been used to create hybrid silver/silver halide nanoparticles. These are formed through partial reduction of Ag⁺ to Ag⁰ by a photochemical self-sensitisation when irradiated with light. This gives the silver/silver halide nanoparticles interesting photocatalytic properties. As such, these silver/silver halide nanoparticles have seen to be part of group of photocatalysts known as plasmonic photocatalysts. Where, the photocatalytic mechanism is enhanced by the surface plasmon resonance of noble metal nanodomains on the surface of the silver halide nanoparticle. The silver/silver halide nanoparticles of Cl⁻, Br⁻ and I⁻ were synthesised and characterised. Silver/silver halide nanoparticles were then incorporated into porous support materials creating silver/silver halide nanocomposite materials. This was through a straight forward aqueous synthesis method, where silver halide nanoparticles precipitated from solution, and nanoparticle size, shape and stabilisation was controlled by the porous support material. Silver/silver halide nanocomposite samples using Cl⁻, Br⁻ and I⁻ were synthesised using wool fibres, kraft paper fibres and nanostructured calcium silicate as supports. UV/Vis and XRD showed Ag⁰ nanodomains were formed during the self-sensitisation process. SEM showed the morphology of the nanocomposites and that the nanoparticles were distributed within the nanocomposite matrix, not deposited on the surface. Preliminary photocatalytic activity of Ag/AgCl nanoparticles and nanocomposites was evaluated through the degradation of methylene blue when irradiated with light. All samples showed increased photocatalytic activity with the Ag/AgCl nanoparticles.</p>