Jean-Yves Cavaillé

Electric anisotropy of carbon nanofibre/epoxy resin composites due to electric field induced alignment

Abstract We report the application of alternating electric fields for the alignment and network formation of carbon nanofibres in an epoxy resin dispersion during curing. In situ optical microscopy verified the electrostatic stabilisation of the fibres in the dispersion and the orientation and agglomeration caused by the electric field. An explanation for the interaction forces between particles and the external electric field is given taking into account electric dipoles induced on the fibres. For the cured composites, the structural anisotropy of the fibre network was evidenced by electrical measurements. A maximal anisotropy for the dc resistivity of about 10 and for the dielectric constant at 1 kHz of about 20 was found for composites with a fibre loading ⩾1 wt.%.

Nucleation and nonisothermal crystallization kinetics in cross-linked polyethylene/zinc oxide nanocomposites

In the present study organic–inorganic hybrid nanocomposites of cross-linked polyethylene (XLPE) with 0, 2, 5 and 10 wt% of trimethoxyoctyl-silane surface treated ZnO nanoparticles were prepared by melt mixing. Non-isothermal crystallization kinetics is examined in detail to reveal the crystallization characteristics of the cross-linked system (XLPE) in the presence of nanomaterials (ZnO) as the dispersed phase. Based on the diffusion controlled growth theory, all the nanocomposites of the present system, exhibit a constant nucleation rate or the growth of nanometer aggregates that constitutes nuclei, with an increasing nucleation rate. Non-isothermal crystallization kinetic parameters and the theoretical estimation of nucleation activity certify the nucleating capability of ZnO nanomaterials in the cross-linked continuous phase of XLPE. The experimental results confirmed that, even at very fast cooling rates, the promising role of nanoparticles for nucleation is able to compensate for the negative effect of fast cooling.

Mechanistic Study and Characterization of Cold-Sprayed Ultra-High Molecular Weight Polyethylene-Nano-ceramic Composite Coating

The cold spray deposition of ultra-high molecular weight polyethylene (UHMWPE) powder mixed with nano-alumina, fumed nano-alumina, and fumed nano-silica was attempted on two different substrates namely polypropylene and aluminum. The coatings with UHMWPE mixed with nano-alumina, fumed nano-alumina, and fumed nano-silica were very contrasting in terms of coating thickness. Nano-ceramic particles played an important role as a bridge bond between the UHMWPE particles. Gas temperature and pressure played an important role in the deposition. The differential scanning calorimetry results of the coatings showed that UHMWPE was melt-crystallized after the coating.

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...

Energy conversion in magneto-rheological elastomers

Abstract Magneto-rheological (MR) elastomers contain micro-/nano-sized ferromagnetic particles dispersed in a soft elastomer matrix, and their rheological properties (storage and loss moduli) exhibit a significant dependence on the application of a magnetic field (namely MR effect). Conversely, it is reported in this work that this multiphysics coupling is associated with an inverse effect (i.e. the dependence of the magnetic properties on mechanical strain), denoted as the pseudo-Villari effect. MR elastomers based on soft and hard silicone rubber matrices and carbonyl iron particles were fabricated and characterized. The pseudo-Villari effect was experimentally quantified: a shear strain of 50 % induces magnetic induction field variations up to 10 mT on anisotropic MR elastomer samples, when placed in a 0.2 T applied field, which might theoretically lead to potential energy conversion density in the mJ cm-3 order of magnitude. In case of anisotropic MR elastomers, the absolute variation of stiffness as a function of applied magnetic field is rather independent of matrix properties. Similarly, the pseudo-Villari effect is found to be independent to the stiffness, thus broadening the adaptability of the materials to sensing and energy harvesting target applications. The potential of the pseudo-Villari effect for energy harvesting applications is finally briefly discussed.

Anisotropic magnetorheological elastomers for mechanical to electrical energy conversion

MagnetoRheological Elastomers (MREs) have been widely used for actuation purposes in numerous applications (e.g., vibration damping), thanks to their magnetic-field controllable shear modulus. Nevertheless, the converse effect, namely, the modification of the magnetic properties through the application of a shear strain or stress has been barely studied. Hence, the purpose of this paper is to investigate such a possibility, both qualitatively and quantitatively, through the modeling of the rotation of particle segments induced both by the mechanical and magnetic solicitations in the case of anisotropic MREs. Such a demonstration, along with experimental validations, therefore allows envisaging new application fields for such materials.