Jean-Marc Chenal

Soft Nanostructured Films with an Ultra-Low Volume Fraction of Percolating Hard Phase

In this study, aqueous emulsion polymerization of n-butyl acrylate is performed in batch conditions without surfactants using a poly(acrylic acid)-trithiocarbonate macro-RAFT agent to control the polymerization and to stabilize the emulsion. According to the polymerization-induced self-assembly (PISA) approach, well-defined amphiphilic PAA-b-PBA diblock copolymers form and self-assemble during synthesis to yield highly stable core-shell particles with an extremely thin hard PAA shell. For the first time, we report here the specific properties of films obtained from these particular latexes. After drying the aqueous dispersion, tough and transparent films are obtained. Although the films are not chemically cross-linked, they do not dissolve in good solvents for PBA. Moreover, they remain transparent even after immersion in water. Rheology shows that the films are both stiff and ductile, thanks to the nanostructured but very low volume fraction (less than 3 wt%) of PAA forming a percolating network in the soft PBA. Compared with conventional core-shell-based films, this approach affords for the first time a route to a thin percolating honeycomb nanostructure with a sharp and strong interface between the two phases. The versatility of the synthetic procedure opens perspectives for a large range of functional materials.

In vitro and in vivo evaluation of a polylactic acid-bioactive glass composite for bone fixation devices

Poly(lactic acid) is nowadays among the most used bioabsorbable materials for medical devices. To promote bone growth on the material surface and increase the degradation rate of the polymer, research is currently focused on organic-inorganic composites by adding a bioactive mineral to the polymer matrix. The purpose of this study was to investigate the ability of a poly(L,DL-lactide)-Bioglass® (P(L,DL)LA-Bioglass(®) 45S5) composite to be used as a bone fixation device. In vitro cell viability testing of P(l,dl)LA based composites containing different amounts of Bioglass(®) 45S5 particles was investigated. According to the degradation rate of the P(L,DL)LA matrix and the cytocompatibility experiments, the composite with 30 wt % of Bioglass® particles seemed to be the best candidate for further investigation. To study its behavior after immersion in simulated physiological conditions, the degradation of the composite was analyzed by measuring its weight loss and mechanical properties and by proceeding with X-ray tomography. We demonstrated that the presence of the bioactive glass significantly accelerated the in vitro degradation of the polymer. A preliminary in vivo investigation on rabbits shows that the addition of 30 wt % of Bioglass(®) in the P(L,DL)LA matrix seems to trigger bone osseointegration especially during the first month of implantation. This composite has thus strong potential interest for health applications.

Single-ion conductor nanocomposite organic–inorganic hybrid membranes for lithium batteries

A modified sol–gel synthesis of di-urethanosil resins provides an easy preparation of single-ion conductor membranes, by combining in one pot the in situ formation of oligosilsesquioxane nanofillers, the cross-linking of PEO chains and the covalent grafting of anion groups. Prototypal membranes demonstrated promising combination of thermal stability, flexibility and lithium ion conductivity performance.

Crystallization processes at the surface of polylactic acid—bioactive glass composites during immersion in simulated body fluid†

We report on the crystallization processes occurring at the surface of PDLLA-Bioglass® composites immersed in simulated body fluid. Composites manufactured by injection molding and containing different amounts (0, 20, 30, and 50 wt %) of 45S5 Bioglass® particles were tested for durations up to 56 days and compared with Bioglass® particles alone. Crystallization processes were followed by visual inspection, X-ray diffraction (with Rietveld analysis) and scanning electron microscopy. Both calcite and hydroxyapatite were formed at the surface of all materials, but their relative ratio was dependent on the Bioglass® content and immersion time. Hydroxyapatite was always the major phase after sufficient immersion time, insuring bioactivity of such composites especially for Bioglass® content higher than 30 wt %. A scenario of crystallization is proposed. Rapid degradation of the composites with 50 wt % was also observed during immersion. Therefore, composites with 30 wt % of Bioglass® particles seem to exhibit the best balance between bioactivity and stability at least during the first weeks of immersion in contact with body fluids.

Effect of nanoclay addition on physical, chemical, optical and biological properties of experimental dental resin composites

OBJECTIVE To prepare organically modified montmorillonite (OM MMT) and assess mechanical, physical, chemical and biological effects of its introduction into resin-composites. METHODS Natural MMT clay was modified by a methacrylate functionalized quaternary ammonium intercalating agent. Interlayer distance was measured by X-ray diffraction. Dental composites were then prepared with x=0, 1, 2.5, 5 or 7.5wt.% of OM MMT, (75-x) wt.% of silanated barium glass and 25wt.% of methacrylate based matrix). Relative weight loss was measured and the effect of the substitution on mechanical properties was studied by dynamic mechanical analysis and hardness tests. Properties of resin composites were evaluated in terms of water sorption, light transmittance, biological tests and by high-performance liquid chromatography (HPLC). RESULTS Resin based composites with well-dispersed organically modified MMT were successfully prepared. There were no significant weight loss differences shown by TGA within all samples. The DMA analysis showed that the introduction of clays have a beneficial effect in increasing the storage and elastic modulus of composites. Clay presence was shown to interfere with the blue light transmittance, affecting Vickers hardness and water sorption levels. The amount of released monomers measured from extracts was below expected levels for this type of materials and biological tests show satisfactory cell compatibility. SIGNIFICANCE This paper reports the successful functionalization of MMT by a methacrylate group and further incorporation in experimental dental composites. Physical and biological results show a potential interest to the application of nanoclays into dental resin composites.

Physical modeling of the electromechanical behavior of polar heterogeneous polymers

Some polymers exhibit very high electromechanical activity, and there is a lack of physical understanding of the mechanisms at the origin of this behavior. In amorphous or slightly crystalline polymers, piezoelectric effect is negligible and the contributions to electrostriction are quadratic function of the applied electric field. These contributions are extrinsic and intrinsic, namely, (i) the electrostatic pressure resulting from the two electrodes attraction (Maxwell effect) and (ii) dipoles-electric field interactions resulting in a mechanism so-called electrostriction. The later contribution can reach much higher value, i.e., by a factor 1000, than the Maxwell effect in some polyurethanes. On the other hand, dipoles-dipoles interactions are known to play a negligible role in homogeneous media. In this work, it is shown that both heterogeneities of local stiffness and dielectric constants are responsible for this unexpected behavior. Nano-heterogeneities may result from phase separation in block copo...

Versatile hybrid sandwich composite combining large stiffness and high damping: spatial patterning of the viscoelastic core layer

With the aim of decreasing CO2 emissions, car producers’ efforts are focused, among others, on reducing the weight of vehicles yet preserving the overall vibrational comfort. To do so, new lightweight materials combining high stiffness and high (passive) damping are sought. For panels essentially loaded in bending, sandwich composites made of two external metallic stiff layers and an inner polymeric (i.e. absorbing) core are broadly used. In the present work, the performances of such sandwich structures are enhanced by optimizing their damping behavior according to their use. More precisely, spatial patterning through selective UV irradiation of the viscoelastic properties of the silicone elastomeric layer is obtained based on a recently published UV irradiation selective technique [1]. Initially developed to modulate the elastic property gradient in Liquid Silicone Rubber (LSR) membranes, the procedure is now generalized to control the viscoelastic behavior of Room Temperature Vulcanization (RTV) silicon...

Tailored microstructure and mechanical properties of nanocomposite films made from polyacrylic/LDH hybrid latexes synthesized by RAFT-mediated emulsion polymerization

Layered Double Hydroxide (LDH)-filled nanocomposites were processed from film-forming latexes synthesized by macroRAFT-assisted encapsulating emulsion polymerization (REEP). The microstructure and thermomechanical behavior of the polymer matrices and corresponding nanocomposites were investigated by TEM, FIB-SEM, SAXS and DMA. Strong ionic interactions created between acrylic acid groups induce lamellar nanostructuration of the P(AA-BA)-b-P(MA-BA) diblock copolymer matrix and are responsible for a high Youngs modulus in the rubbery state that increases with the length (i.e., the molar mass) of the P(AA-BA) blocks. When filled with 16 wt% of LDH, the intrinsic structure of the matrix is lost and the mechanical behavior of the nanocomposites is solely driven by the LDH dispersion and ionic interactions. Two types of percolation (i.e., mesh size of the LDH network and mechanical reinforcement) have been achieved by playing with the degree of segregation of the LDH nanoplatelets within the material.