Jean-Charles Eloi

Metallopolymers with emerging applications

A wide variety of metal-containing polymers, or ‘metallopolymers’, have become readily available over the past decade. This has led to a rapidly expanding interest in their properties and uses. These new materials combine the processing advantages of polymers with the functionality provided by the presence of metal centers. We illustrate a selection of applications of metallopolymers in areas such as sensors, memory and light-emitting devices, solar cells, nanolithography, photonic crystal displays, controlled release, and catalysis.

Stimulus-Responsive Self-Assembly: Reversible, Redox-Controlled Micellization of Polyferrocenylsilane Diblock Copolymers

In depth studies of the use of electron transfer reactions as a means to control the self-assembly of diblock copolymers with an electroactive metalloblock are reported. Specifically, the redox-triggered self-assembly of a series of polystyrene-block-polyferrocenylsilane (PS-b-PFS) diblock copolymers in dichloromethane solution is described. In the case of the amorphous polystyrene(n)-b-poly(ferrocenylphenylmethylsilane)(m) diblock copolymers (PS(n)-b-PFMPS(m): n = 548, m = 73; n = 71, m = 165; where n and m are the number-averaged degrees of polymerization), spherical micelles with an oxidized PFS core and a PS corona were formed upon oxidation of more than 50% of the ferrocenyl units by [N(C(6)H(4)Br-4)(3)][SbX(6)] (X = Cl, F). Analogous block copolymers containing a poly(ferrocenylethylmethylsilane) (PFEMS) metalloblock, which has a lower glass transition temperature, behaved similarly. However, in contrast, on replacement of the amorphous metallopolymer blocks by semicrystalline poly(ferrocenyldimethylsilane) (PFDMS) segments, a change in the observed morphology was detected with the formation of ribbon-like micelles upon oxidation of PS(535)-b-PFDMS(103) above the same threshold value. Again the coronas consisted of fully solvated PS and the core consisted of partially to fully oxidized PFS associated with the counteranions. When oxidation was performed with [N(C(6)H(4)Br-4)(3)][SbF(6)], reduction of the cores of the spherical or ribbon-like micelles with [Co(η-C(5)Me(5))(2)] enabled full recovery of the neutral chains and no significant chain scission was detected.

Energy barrier distribution for dispersed mixed oxide magnetic nanoparticles

Mixed Fe/Co oxide nanoparticles, diameter 8 nm, were prepared using the protein ferritin as a template and characterized by transmission electron microscopy (TEM) and Raman spectroscopy. We show that the latter effectively distinguishes between magnetite (Fe3O4), maghemite (γ-Fe2O3) and Co ferrite (CoxFe3-xO4). Zero-field-cooled susceptibility measurements show isolated magnetite nanoparticles have a blocking temperature TB = 18 ± 1 K, but that adding 0.5% Co raises TB to 30 K. Data for thermal relaxation from saturation obey a T ln(t/τ0) scaling, enabling us to determine the energy barrier distributions for the dispersed nanoparticles. For Fe oxide only a single peak was found. However, with the addition of only 0.5% Co a second component is observed that decreases rapidly with increasing energy.

Top-down design of magnonic crystals from bottom-up magnetic nanoparticles through protein arrays

We show that chemical fixation enables top-down micro-machining of large periodic 3D arrays of protein-encapsulated magnetic nanoparticles (NPs) without loss of order. We machined 3D micro-cubes containing a superlattice of NPs by means of focused ion beam etching, integrated an individual micro-cube to a thin-film coplanar waveguide and measured the resonant microwave response. Our work represents a major step towards well-defined magnonic metamaterials created from the self-assembly of magnetic nanoparticles.

Protein brownian rotation at the glass transition temperature of a freeze-concentrated buffer probed by superparamagnetic nanoparticles

For applications from food science to the freeze-thawing of proteins it is important to understand the often complex freezing behavior of solutions of biomolecules. Here we use a magnetic method to monitor the Brownian rotation of a quasi-spherical cage-shaped protein, apoferritin, approaching the glass transition Tg in a freeze-concentrated buffer (Tris-HCl). The protein incorporates a synthetic magnetic nanoparticle (Co-doped Fe3O4 (magnetite)). We use the magnetic signal from the nanoparticles to monitor the protein orientation. As T decreases toward Tg of the buffer solution the proteins rotational relaxation time increases exponentially, taking values in the range from a few seconds up to thousands of seconds, i.e., orders of magnitude greater than usually accessed, e.g., by NMR. The longest relaxation times measured correspond to estimated viscosities >2 MPa s. As well as being a means to study low-temperature, high-viscosity environments, our method provides evidence that, for the cooling protocol used, the following applies: 1), the concentration of the freeze-concentrated buffer at Tg is independent of its initial concentration; 2), little protein adsorption takes place at the interface between ice and buffer; and 3), the protein is free to rotate even at temperatures as low as 207 K.

Preparation of Swellable Hydrogel-Containing Colloidosomes from Aqueous Two-Phase Pickering Emulsion Droplets

The fabrication of stable colloidosomes derived from water-in-water Pickering-like emulsions are described that were produced by addition of fluorescent amine-modified polystyrene latex beads to an aqueous two-phase system consisting of dextran-enriched droplets dispersed in a PEG-enriched continuous phase. Addition of polyacrylic acid followed by carbodiimide-induced crosslinking with dextran produces hydrogelled droplets capable of reversible swelling and selective molecular uptake and exclusion. Colloidosomes produced specifically in all-water systems could offer new opportunities in microencapsulation and the bottom-up construction of synthetic protocells.