Magnetic Self-Assembling of spherical Co nanoparticles used as building blocks: Syntheses, properties and theory

International audienceIn this chapter, we show that thanks to the use of micellar and organometallic approaches, one can favor the growth of uniform spherical Co NPs with controlled surface passivation (dodecanoic acid or oleylamine), tunable size (from around 4 to 9 nm) and tunable nanocrystallinity (from fcc to hcp structure). As a result of the balance between van der Waals attractions between the metallic NPs, magnetic interactions between the magnetic NPs and solvent-mediated interactions between ligands, these uniform colloidal NPs can be used as building units to form a full set of assemblies which morphology depends on the deposition strategy, involving solvent evaporation. In the case of spontaneous self-assembling of magnetic NPs, compact hexagonal 2D arrays and 3D superlattices called supercrystals can form. In the latter case, either face-centered cubic supercrystalline films or single colloidal crystals can be obtained. Mesostructures of hexagonally ordered columns, labyrinths and void structures can result from assisted self-assembling, induced by the application of an external magnetic field. In highly ordered superlattices, individual NPs act as “artificial atoms” and occupy the lattice sites to form repetitive, periodic “artificial planes". From a fundamental point of view, these artificial solids constitute good models for investigating crystallization behavior. Resulting from collective interactions between neighboring NPs, they exhibit novel magnetic properties. The magnitude of these interactions, and then, the magnetic properties, can be tuned by various parameters including (1) the (crystallographic) nature of the magnetic NP, (2) the NP size, (3) the nature of the coating agent, (4) the nature of the solvent, (5) the evaporation rate and (6) if appropriate, the application of an external field during the solvent evaporation. On the one hand, simulations based on a flory-type solvation theory using Hansen solubility colloidal parameters allow to predict the cobalt NP size. On the other hand, Monte Carlo simulations and free energy theories are able to predict the size and type of patterns appearing during the evaporation of a solution of magnetic NPs under a magnetic fiel

Analytical methods for lignocellulosic biomass structural polysaccharides

The use of lignocellulosic biomass has been postulated as a potential pathway toward diminishing global dependence on nonrenewable sources of chemicals and fuels. Before a specific feedstock can be selected for biochemical conversion into biofuels and bio-based chemicals, it must first be characterized to evaluate the chemical composition of the cell walls. Polysaccharides, specifically cellulose and hemicellulose, are often the focal point of these appraisals, since these constituents are the dominant substrates converted into monomeric sugars like glucose and xylose. These monosaccharides can be transformed, using microorganisms like yeast, into substances such as ethanol. Plant species containing abundant polysaccharides are highly desirable, as higher quantities of sugars should translate into larger end-product yields. Given the vast pool of potential feedstocks, qualitative and quantitative analytical methods are needed to assess cell wall polysaccharides. Many of these tools, such as wet chemical and chromatographic techniques, have been ubiquitously used for some time. Shortcomings in these analyses, however, prevent their usage in screening large sample sets for quintessential, high-yield, fuel-producing traits. This chapter briefly summarizes how analytical spectroscopy can lessen some of these limitations and how it has been utilized for polysaccharide analysis