A benzoxazine/substituted borazine composite coating: A new resin for improving the corrosion resistance of the pristine benzoxazine coating applied on aluminum

In this paper, laboratory synthesized Phenol-paraPhenyleneDiAmine (P-pPDA) benzoxazine containing different amounts of B-trimesityl-N-triphenylborazine was applied by spin coating on aluminum and thermally cured. The addition of the borazine derivative (borazine 1) does not appear to modify the curing characteristics of the P-pPDA matrix itself as shown by FTIR, DSC and DEA analyses; however, some interactions - chemical and/or physical (co-crystallization) – between P-pPDA and borazine 1 cannot be excluded. The microstructure of the composites is characterized by a two phase system consisting of a dispersion of nanosized (10–20 nm) clusters for the lowest borazine 1 concentration (0.5 wt%), evolving towards bigger (100–200 nm), agglomerated clusters for higher borazine 1 concentrations (3 wt%) and finally, continuous, dendritic structures within the P-pPDA matrix for the highest borazine 1 concentration (10 wt%). The benzoxazine composite coating containing 0.5 wt% trimesitylborazine derivative showed a largely increased and durable ability to protect the aluminum substrate. It is shown that a highly capacitive behavior and durable barrier properties can be obtained for P-pPDA coatings containing such a low amount of borazine derivative homogeneously dispersed in the benzoxazine matrix. For concentrations of 3 wt%, as agglomeration took place and dendrites appeared for the highest concentration of borazine derivative (10 wt%), the corrosion resistance decreased with time

Quantifying the local mechanical properties of twisted double bilayer graphene

Nanomechanical measurements of minimally twisted van der Waals materials remained elusive despite their fundamental importance for device realisation. Here, we use Ultrasonic Force Microscopy (UFM) to locally quantify the variation of out-of-plane Young's modulus in minimally twisted double bilayer graphene (TDBG). We reveal a softening of the Young's modulus by 7% and 17% along single and double domain walls, respectively. Our experimental results are confirmed by force-field relaxation models. This study highlights the strong tunability of nanomechanical properties in engineered twisted materials, and paves the way for future applications of designer 2D nanomechanical systems

Microstructure et propriétés de transport: les fibres de carbone

Doctorat en Sciences appliquées -- UCL, 199

Nanomechanics with the atomic force microscope on polymer surfaces, interfaces and nano-materials

Methods based on the atomic force microscope (AFM) were implemented or developed to measure and map at the nanoscale the mechanical properties of polymer surfaces and of nanomaterials: force spectroscopy, force modulation, phase detection in intermittent-contact mode. Especially, a technique, referred as resonant contact-AFM, was developed. It is based on the electrostatic excitation of the cantilever vibration and on the measurement of its resonance frequency when the tip contacts the probed sample. A theoretical model was developed to determine the tip-sample contact stiffness from the measurement of the frequency shift. These methods were used to study several questions raised in the fields of polymer surfaces and interfaces and of nanomaterials. Surfaces of toughened polypropylene (PP) with ethylene-propylene copolymer (EP) were studied by force spectroscopy and force modulation microscopy (FMM) to characterise the effect of the blending and the moulding processes and the PP/EP viscosity ratio on the surface distribution of the EP rubber nodules. The contribution of the EP rubber to paint adhesion was also demonstrated. Surfaces of atactic polypropylene photo-grafted with acrylic acid monomers were analysed by intermittent-contact AFM (IC-AFM) with phase detection. The combination of these methods with other analytical techniques allowed characterising the chemical composition of the heterogeneous surface morphology obtained after photo-grafting. The tensile elastic modulus of polymer nanotubes and metallic nanowires was measured with force spectroscopy and resonant contact-AFM. These measurements confirmed the ability of resonant contact-AFM to quantitatively measure the mechanical properties of nanomaterials. Moreover, they showed that the measured modulus increased when the nanowires or nanotubes diameter decreases. This behaviour was explained by taking into account the effect of the surface deformation that added a surface stiffness proportional to the surface tension, or surface stress, of the material. Resonant contact-AFM was also used to characterise the variation of the mechanical properties at the interfaces in polymer blends. It was demonstrated that this technique allows the determination of the interfacial width in incompatible polymer blends. It also allowed characterising the mechanical property gradient that can appear in reactive polymer blends.(FSA 3A)--UCL, 200

Scanning Probe Microscopies : Principles and Applications to Micro- and Nano-Fibers

This chapter presents the main principles of Scanning Electron Tunneling (STM) and atomic force microscopy (AFM) and describes the most generally used techniques. It also presents some applications on micro- and nanofibers. Since many different kinds of interactions can be measured between the probe and the sample, a large variety of techniques were developed. The three main parts of an STM are the probe, a conductive tip, a piezoelectric scanner, and a control unit. A measurement head contains a support on which a soft microcantilever with an ultra-fine tip at its end is mounted and an optical detection system enables the measurement of the deflection of the cantilever. In the “constant force” mode, the cantilever deflection signal is measured while the sample is raster scanned under the tip. Combining AFM and nanoindentation, several authors have studied the hardness and the elastic modulus of metallic and semiconducting nanowires. Lateral force microscopy was also used to measure the mechanical properties of nanowires

Les microscopies a sonde locale: de l'imagerie des atomes aux spectroscopies a l'echelle nanoscopique

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Nanotechnology (invited lecture)

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Atomic Force Microscopies of polymers : From the molecular structure to the viscoelasticity of blends (invited lecture)

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