In situ Formation of Plasmonic Gold Nanoparticles in Ordered Block Copolymer Films

Context: Metamaterials are of current interest for their unique optical properties. Although they are traditionally obtained by lithography, bottom-up ways of fabrication are now investigated for a precise nanometric control of the structure, through self-assembly and nanochemistry. To this end, organized films containing gold nanoparticles are widely studied for they combine the controlled structure of a film to the plasmonic properties of these nanoparticles. We report here the $in\ situ$ formation of gold nanoparticles (AuNPs) in a polystyrene-$block$-poly(vinylpyridine) (PS-b-PVP) copolymer solution, then cast as AuNP containing ordered films. By use of an appropriate solvent, casting a block colymer solution can form films of oriented cylinders (perpendicular or parallel to the substrate). The addition of gold salt $_Au$($III$)$chloride$($AuCl_3$)-followed by ultra-sound treatment before casting the film gives birth to spherical AuNPs (2-3 nm in size) located, after deposition, inside the cylinders. For parallel cylinders, AuNPs are found to redirect them to a quasi-perpendicular orientation, while no major perturbation is found for the perpendicular cylinders. Larger spherical AuNPs (3-4 nm) exhibiting a plasmon resonance are also obtained by successive additions of gold salt to the AuNPs and locate equally inside the cylinders after casting the film. This method of $in\ situ$ insertion of AuNPs in patterned films provides nanocomposite materials with plasmonic properties and opens new ways for the preparation of metamaterials

Ligand-free synthesis of gold nanoparticles included within cylindrical block copolymer films

International audienceWe report the inclusion of gold nanoparticles (AuNPs) without pre-functionalization step in oriented films of block copolymer poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP) on a substrate. After deposition with an appropriate solvent, PS-b-P4VP and PS-b-P2VP are cast as films presenting either perpendicular and parallel cylinders. By including gold salt in these solutions and operating subsequent sonication, AuNPs (with a diameter of 2 nm) are synthetized and found located inside the cylinders of PVP after deposition of the film by spin-coating. Increasing the initial amount of gold precursors allows the formation of biggerAuPs (d=4 nm). The seeded-growth of the pre-formed AuNPs was also achieved in order to get bigger AuNPs (d=8 nm) with plasmon resonance properties. This method was found more efficient in order to get bigger nanoparticles with a low quantity of gold precursor. The presence of AuNPs in the PVP domains disturbs the organization of the parallel cylinders, while it swells the PVP domains in the case of the perpendicular cylinders without changing their orientation. The formation of AuNPs inside a copolymer was also performed by radiolysis, through the irradiation of the copolymer solution and the copolymer film, bothcontaining the gold salt, and led to similar results. The presence of plasmonic AuNPs of small diameter ($\sim$3-4 nm) was evidenced in both cases. GISAXS measurements are presented to characterize and compare the films order before and after gold inclusion, and help proving that cylinder are perpendicular to the substrate through the entire thickness

Imogolite nanotubes partially transformed by decylphosphonic acid to form an interface active composite material

International audienceThe natural Imogolite clay ((HO)$_3$Al$_2$O$_3$SiOH) with nano-tubular structure of 2-3 nm diameter is apromising candidate for polymer reinforcement, water treatment and other applications. However,its hydrophilic external gibbsite like surface limits its use in hydrophobic environment. Among thedifferent possible grafting functions for the outer surface, the phosphonic acid moiety is the most used.It shows strong reactivity with imogolite. If the resulting product can be dispersed in a hydrophobicenvironment, the impact of the reaction on the tubular structure was never demonstrated andexperimental evidence of grafted dispersed imogolite tubes with a brush-like layer on their exterior isstill missin

Partial Transformation of Imogolite by Decylphosphonic Acid Yields an Interface Active Composite Material

International audienceThe phosphonic acid moiety is commonly used as an anchoring group for the surface modification of imogolite. However, the impact of the reaction on its structure has never been clearly analyzed before. We study the reaction of imogolite and decylphosphonic acid by combining infrared spectroscopy, X-ray scattering, scanning electron microscopy, transmission electron microscopy and solid-state nuclear magnetic resonance spectroscopy. Instead of a surface functionalization, we observe the formation of a lamellar phase interconnected with imogolite bundles. Although we find no evidence for grafted imogolite tubes, we observe the expected dispersion characteristics and stabilization of water in toluene emulsions described in literature. Based on the surface chemistry of imogolite we propose an explanation for the observed reactivity and link the structural features of the obtained composite material to its dispersibility in toluene and its observed properties at the toluene-water interface

Ligand-free synthesis of gold nanoparticles included within cylindrical blocl copolymer films

International audienceWe report a method to include non-functionalized gold nanoparticles (AuNPs) in oriented cylindrical phases of poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP) block copolymers, perpendicular or parallel to a substrate. The combination of AFM, TEM, GISAXS and spectroscopy allows a complete characterization of the nanocomposite. AuNPs are produced by the ultra-sound reduction of a gold salt in the copolymer solution, prior to the deposition of the film by spin-coating. The AuNPs are found to be located within the PVP cylinders exclusively. Sizes from 2 to 4 nm are tuned as a function of the initial gold salt concentration. A seeded-growth of these pre-formed AuNPs was also achieved by a further ultra-sound treatment to produce larger AuNPs (up to d=10 nm) with plasmon resonance properties. For parallel cylinders, the presence of AuNPs in the PVP domains disturbs the organization, while, for perpendicular cylinders, the PVP domains are swollen without any change in their orientation. The synthesis of AuNPs inside the copolymer was also performed by radiolysis, through the irradiation of the copolymer solution or the copolymer film, both containing the gold salt. In these cases, the presence of plasmonic AuNPs was also evidenced. Offering a control of the AuNPs size (< 2 nm to 10 nm) and location, the presented method is a unique way of inserting plasmonic AuNPs into oriented cylinders for reaching anisotropic geometries of valuable interest for optic

Ligand-free synthesis of gold nanoparticles incorporated within oriented cylindrical block copolymer films

Mixing gold nanoparticles with nanostructured block copolymer films is a self-assembled way of building potential optical metamaterials. We report here the inclusion of gold nanoparticles (AuNPs) without pre-functionalization step in oriented films of block copolymer poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP) on a substrate. After deposition with an appropriate solvent, PS-b-P4VP and PS-b-P2VP are cast as films presenting either perpendicular and parallel cylinders. By including gold salt in these solutions and operating subsequent sonication, AuNPs (with a diameter of 2 nm) are synthetized and found located inside the cylinders of PVP (Fig.1) after deposition of the film by spin-coating. 1 Increasing the initial amount of gold precursors allows the formation of bigger AuPs (d=4 nm). The seeded-growth of the pre-formed AuNPs was also achieved in order to get bigger AuNPs (d=8 nm) with plasmon resonance properties. This method was found more efficient in order to get bigger nanoparticles with a low quantity of gold precursor. The presence of AuNPs in the PVP domains disturbs the organization of the parallel cylinders, while it swells the PVP domains in the case of the perpendicular cylinders without changing their orientation. The formation of AuNPs inside a copolymer was also performed by radiolysis, through the irradiation of the copolymer solution and the copolymer film, both containing the gold salt, and led to similar results. The presence of plasmonic AuNPs of small diameter ($\sim$3-4 nm) was evidenced in both cases. GISAXS measurements are presented to characterize and compare the films order before and after gold inclusion, and help proving that cylinder are perpendicular to the substrate through the entire thickness. If time allows, first optical characterizations of the polymer-gold films will be presented

Ligand-free synthesis of gold nanoparticles incorporated within oriented cylindrical block copolymer films : towards optical metamaterials

We report a method to incorporate non-functionalized gold nanoparticles (AuNPs) in oriented cylindrical phases of poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP) block copolymers, perpendicular to a substrate. The combination of AFM, TEM, GISAXS and spectroscopy allows complete characterization of the nanocomposites. AuNPs are produced by the ultra-sound reduction of a gold salt in the copolymer solution, prior to the deposition of the films by spin-coating. The AuNPs are found to be located within the PVP cylinders exclusively. The seeded-growth of these pre-formed AuNPs by a further ultra-sound treatment produced plasmonic AuNPs (up to d =10 nm). For perpendicular cylinders, the PVP domains are swollen without any change in their orientation. Ellipsometric optical properties of these plasmonic AuNPs embeded into oriented cylinders show a definite extinction in reflectivity at a precise energy and incidence angle

Nanotubes d'imogolite associés à des nanoparticules d'or. Impact du mode de préparation sur la réactivité sous éclairement UV et visible

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