Jean-Michel Thomassin

Straightforward synthesis of conductive graphene/polymer nanocomposites from graphite oxide

The reduction of graphite oxide (GO) in the presence of reactive poly(methyl methacrylate) (PMMA), under mild biphasic conditions, directly affords graphene grafted with PMMA. The resulting nanocomposite shows excellent electrical conductivities resulting from the optimal dispersion and exfoliation of graphene in the polymer matrix.

CO2-blown microcellular non-isocyanate polyurethane (NIPU) foams: from bio- and CO2-sourced monomers to potentially thermal insulating materials

Bio- and CO2-sourced non-isocyanate polyurethane (NIPU) microcellular foams were prepared using supercritical carbon dioxide (scCO2) foaming technology. These low-density foams offer low thermal conductivity and have an impressive potential for use in insulating materials. They constitute attractive alternatives to conventional polyurethane foams. We investigated CO2s ability to synthesize the cyclic carbonates that are used in the preparation of NIPU by melt step-growth polymerization with a bio-sourced amino-telechelic oligoamide and for NIPU foaming. Our study shows that CO2 is not only sequestered in the material for long-term application, but is also valorized as a blowing agent in the production of NIPU foams. Such foams will contribute to energy conservation and savings by reducing CO2 emissions.

Drug loading of polymer implants by supercritical CO2 assisted impregnation: A review

Drug loaded implants also called drug-eluting implants have proven their benefits over simple implants. Among the developed manufacturing processes, the supercritical CO2 (scCO2) assisted impregnation has attracted growing attention to load Active Pharmaceutical Ingredients into polymer implants since it enables to recover a final implant free of any solvent residue and to operate under mild temperature which is suitable for processing with thermosensitive drugs. This paper is a review of the state-of-the-art and the application of the scCO2 assisted impregnation process to prepare drug-eluting implants. It introduces the process and presents its advantages for biomedical applications. The influences of the characteristics of the implied binary systems and of the experimental conditions on the drug loading are described. Then, the various current applications of this process for manufacturing drug-eluting implants are reviewed. Finally, the new emerging variations of this process are described.

Electromagnetic Absorption Properties of Carbon Nanotube Nanocomposite Foam Filling Honeycomb Waveguide Structures

Carbon nanotube reinforced polymer foams filling a metallic honeycomb were processed and characterized for the production of hybrid materials with high electromagnetic absorption potential. Electromagnetic modeling and experimental characterization of the hybrids proved that the honeycomb, acting as a hexagonal waveguide, improves the absorption properties in the gigahertz range above the cutoff frequency. The electromagnetic absorption can be tuned by changing the hybrid material properties. The required levels of electrical conductivity are attained owing to the dispersion of low amounts (1-2 wt%) of carbon nanotubes inside the polymer matrix. The combination of the foam and honeycomb architecture contributes to decrease the real part of the relative effective permittivity Re{εr,eff }. Varying the cell shape of the honeycomb changes the frequency range for high absorption. An analytical model for the absorption has been developed, showing good agreement with the experimental results.

Carbon nanotube composites for broadband microwave absorbing materials

In this paper, we present a new shielding and absorbing composite based on carbon nanotubes (CNTs) dispersed inside a polymer dielectric material. The extremely high aspect ratio of CNTs and their remarkable conductive properties lead to good absorbing properties with very low concentrations. A broadband characterization technique is used to measure the microwave electrical properties of CNT composites. It is shown that a conduction level of 1 S/m is reached for only 0.35 wt % of a CNT, while, for a classical absorbing composite based on carbon black, 20% concentration is mandatory. The conductive properties are explained by a phenomenological electrical model and successfully correlated with rheological data aiming at monitoring the dispersion of conductive inclusions in polymer matrices

Double thermoresponsive di- and triblock copolymers based on N-vinylcaprolactam and N-vinylpyrrolidone: Synthesis and comparative study of solution behaviour

Poly(N-vinylcaprolactam) (PNVCL) and poly(N-vinylpyrrolidone) (PNVP) are water soluble polymers of interest especially in the biomedical field. Moreover, PNVCL is characterized by a lower critical solution temperature close to 36 °C in water, which makes it useful for the design of thermoresponsive systems. In this context, we used the cobalt-mediated radical polymerization (CMRP) and reaction coupling (CMRC) for synthesizing a series of well-defined NVCL and NVP-based copolymers, including statistical copolymers as well as double thermoresponsive diblocks and triblocks. Dynamic light scattering and turbidimetry analyses highlighted the crucial impact of the copolymer composition and architecture on the cloud point temperature (TCP) of each segment and also their influence on the multistep assembly behaviour of block copolymers. Addition of NaCl enabled us to adjust the inter-TCP range of the di- and triblock in which selective precipitation of one block and self-assembly of the copolymer were favoured. Overall, data presented here provide a basis for the synthesis of a broad range of NVCL/NVP based copolymer architectures with a tunable thermal response in water.

Double thermo-responsive hydrogels from poly(vinylcaprolactam) containing diblock and triblock copolymers

The thermally-induced gelation and gel properties of concentrated aqueous solutions of double thermoresponsive poly(N-vinylamide)-based di- and triblock copolymers are studied by rheology. The copolymers under investigation, prepared by cobalt-mediated radical polymerization and coupling reactions, are composed of poly(vinylcaprolactam) (PNVCL) blocks and of a statistical poly(vinylcaprolactam-stat-vinylpyrrolidone) segment with a cloud point temperature (TCP) higher than that of PNVCL. Heating the di- and triblock solutions beyond the first phase transition temperature favors gel formation while heating above the second TCP leads to opaque gels without macroscopic demixing. Moduli of the triblock hydrogels are systematically higher than those of the corresponding diblocks, even above the second transition. Rheological data suggest distinct micellar structures for each copolymer architecture: densely packed micelles of diblocks and 3-D networks of bridged micelles for triblocks. Strain sweep experiments also emphasize the positive effect of the micelle bridging on the elasticity and stability of the hydrogels. The formation and properties of the obtained gels are also shown to depend on the copolymer concentration, block length, and composition. Addition of salt also allows us to tune the phase transition temperatures of these double thermoresponsive hydrogels.

Characterization and optimization of GMO-based gels with long term release for intraarticular administration

Osteoarthritis is characterized by slow degenerative processes in the articular cartilage within synovial joints. It could be interesting to develop a sustained-release formulation that could be effective on both pain/inflammation and restoration of mechanical integrity of the joint. Recently, an injectable system based on glycerol monooleate (GMO), containing clonidine as a model hydrophilic analgesic/anti-inflammatory drug and hyaluronic acid as a viscoelastic scaffold, showed promising potential as a biodegradable and biocompatible preparation to sustain the drug activity. However, drug release from the system is relatively fast (complete within 1 week) and the underlying drug release mechanisms not fully understood. The aims of this study were: (i) to significantly improve this type of local controlled drug delivery system by further sustaining clonidine release, and (ii) to elucidate the underlying mass transport mechanisms. The addition of FDA-approved inactive ingredients such as sodium oleate or purified soybean oil was found to be highly effective. The release rate could be substantially reduced (e.g., 50% release after 10 days), due to the increased hydrophobicity of the systems, resulting in slower and reduced water uptake and reduced drug mobility. Interestingly, Ficks second law of diffusion could be used to quantitatively describe drug release.

Locating carbon nanotubes (CNTs) at the surface of polymer microspheres using poly(vinyl alcohol) grafted CNTs as dispersion co-stabilizers

In this communication, we prepared carbon nanotubes (CNTs) modified by poly(vinyl alcohol) that are used as co-stabilizers for the dispersion polymerization of methyl methacrylate. Poly(methyl methacrylate) microspheres with CNTs selectively located at their surface are formed. This specific localization is a way to enhance the electrical conductivity of the nanocomposite.

Microwave absorbers based on foamed nanocomposites with graded concentration of carbon nanotubes

A multilayered foamed nanocomposite with graded concentration of carbon nanotubes is proposed as a novel microwave absorber. The dispersion and foaming process enables to control the gradation in conductivity of each layer. Absorption performances are demonstrated through measurements of reflectivity and shielding effectiveness over the frequency range [8-16 GHz]. An improvement of about 5 dB in reflectivity is observed with respect to a foamed composite having a similar uniform concentration, while in both cases the shielding effectiveness is kept higher than 15 dB.