The ability to have predictive behavior of nanoparticles during bottom-up fabrication requires a fundamental understanding of their mechanical properties, often differing from their bulk counterparts because of the dramatic difference in grain size and free surfaces. Here, a series of in situ nanocompression experiments is performed on cerium oxide nanocubes in an environmental transmission electron microscope, in which the operating conditions of electron dose and gaseous environment are changed. This leads to either oxidation or reduction of the nanoparticles in situ. Utilizing the same nanoparticle under different oxidative states allows a direct comparison of the mechanical property changes. The elastic properties of CeO _x nanocubes, 1.5< x < 2 , are compared to the results from a DFT + U simulation. The trends from the two treatments are in general agreement.

HYPOTHESIS:To understand the relationship between topography and wetting, it is not enough to study the contact angle. Indeed, the liquid-solid interface plays an important role in wetting. However, data such as the total triple line length, the wetting area and the anchoring depth are inaccessible or difficult to obtain experimentally. This work proposes to overcome the experimental limitations by using a numerical approach to characterize the wetting behavior on textured surfaces.METHODS:The wetting behavior of an anisotropic textured surface was compared for both experimental and numerical approaches. The experimental wetting is characterized by sessile drop experiments. The simulations were performed by applying the pseudo-potential Lattice-Boltzmann method. The numerical approach was then used to predict the wetting behavior of different materials.FINDINGS:The simulations capture both the wetting state and the contact angle, in accordance with the experimental observation. Without making any assumptions about the interfacial shape and anchoring, the simulation allows to characterize the liquid-solid interface by quantifying the total length of the triple line and the wetting area. Simultaneously, the simulations enable the characterization of impregnation within textures for complex mixed regimes.

The understanding and modeling of heat transport across nanometer and subnanometer gaps, where the distinction between thermal radiation and conduction becomes blurred, remains an open question. In this work, we present a three-dimensional atomistic simulation framework by combining the molecular dynamics (MD) and phonon nonequilibrium Green???s function (NEGF) methods. The relaxed atomic configuration and interaction force constants of metallic vacuum nanogaps are generated from MD as inputs into harmonic phonon NEGF. Phonon tunneling across gold-gold and copper-copper nanogaps is quantified, and is shown to be a significant heat transport channel below a gap size of 1 nm. We demonstrate that lattice anharmonicity contributes to within 20%???30% of phonon tunneling depending on gap size, whereas electrostatic interactions turn out to have a weak effect for the small bias voltage typically used in experimental measurements. This work provides detailed information of the heat current spectrum and interprets the recent experimental determination of thermal conductance across gold-gold nanogaps. Our study contributes to deeper insight into heat transport in the extremely near-field regime, as well as hints for future experimental investigation.

The tribological behavior of different linear amines blended to PAO4 alone or in combination with ZDDP was investigated under boundary lubrication regime via the coupling of tribometry and XPS measurements. Using a reciprocating ball-on-flat tribometer, it was evidenced that all tested amines were able to reduce both friction and wear. The combination of primary monoamine (1 wt %) and ZDDP (1 wt %) produced synergistic effect on reduction of both friction and wear in most cases. Experimental investigations suggest that this synergistic effect is due to the fast formation of a zinc-oxide-enriched tribofilm depleted in phosphates. Moreover, our results show that the lubrication mechanism and the composition of the tribofilm are strongly dependent on the amine/ZDDP molar ratio.

The tribological performance of the R1233zd refrigerant in extreme confinement between two hematite $${\text{Fe}}_{ 2} {\text{O}}_{ 3} \left( {01\overline{1} 2} \right)$$ surfaces is studied thanks to large-scale molecular dynamics simulations based on a force field previously parametrized from ab initio calculations. With atomically smooth surfaces, and a refrigerant film thickness as small as 2 nm, adsorbed layers of R1233zd molecules on $${\text{Fe}}_{ 2} {\text{O}}_{ 3}$$ surfaces resist to high pressures and high sliding velocities. In ultra-confined systems, friction behaves non-monotonously, reaching a global maximum when a single saturated layer is formed. Moreover, sliding simulations with a rough surface reveal total film breakdown for a local pressure around 13 GPa. Interestingly, the addition of a sliding velocity enhances the performance through a hydrodynamic lift-like mechanism: the higher the sliding, the higher the chance for refrigerant molecules to be entrained into the asperity contact.

The adsorption phenomenon of refrigerant R-1233zd(E) molecules on a hematite Fe2O3(011 (1) over bar2) surface is studied at the quantum level thanks to density functional theory + U (DFT + U) calculations employing a van der Waals functional combined with a spin-polarized system. The results show different adsorption sites on the solid surface depending on orientations of the molecule, characterizing strong interactions between the refrigerant molecule and both iron and oxygen atoms. A range of binding energy values of -0.92 to -0.22 eV is observed. These ab initio results are used to parametrize a force field at the refrigeranthematite interface for larger scale molecular dynamics simulations. Effects of these ab initio considerations on density and velocity profiles are studied, in the case of a confined fluid between two surfaces as in a lubricated contact. The high binding energy values induce a locking effect of the R-1233zd(E) molecules close to the hematite surface, showing a resistance to compression (P-z = 500 MPa) and shearing (v(s) = 20 m/s).

In situ mechanical testing inside Transmission Electron Microscopes is probably the most powerful way to investigate the mechanical behavior at the nanoscale, as it can provide simultaneously quantitative mechanical data (force-displacement curves) and images of the sample during deformation [1]. Such experiments not only permit insightful works on plasticity mechanisms in bulk materials, with characterizations before/during/after conventional mechanical tests, but also permit the analysis of the mechanical behavior of individual nano-objects.