Contact laws between nanoparticles: the elasticity of a nanopowder

Abstract

Studies of the mechanical contact between nanometer-scale particles provide fundamental insights into the mechanical properties of materials and the validity of contact laws at the nanoscale which are still under debate for contact surfaces approaching atomic dimensions. Using in situ Brillouin light scattering under high pressure, we show that effective medium theories successfully predict the macroscopic sound velocities in nanopowders if one takes into account the cementation of the contacts Our measurements suggest the relevance of the continuum approach and effective medium theories to describe the contact between nanoparticles of diameters as small as 4 nm, i.e. with radii of contact of a few angstroms. In particular, we demonstrate that the mechanical properties of nanopowders strongly depend on the surface state of the nanoparticles. The presence of molecular adsorbates modifies significantly the contact laws.

Room temperature plasticity and phase transformation of nanometer-sized transition alumina nanoparticles under pressure

“…Three uniaxial compression experiments have been performed at 5 GPa, 15 GPa and 20 GPa. As shown recently, the pressure measured by the ruby luminescence even in presence of highly non-hydrostatic components is a pertinent parameter to study the mechanical properties of a nanopowder by giving an average pressure that corresponds to the load on the powder [28]. Thin foils have been extracted from the compacted samples using a FIB/SEM (NVision 40; Carl Zeiss Microscopy GmbH, Oberkochen, Germany), equipped with a multi-nozzle SIINT gas injection system (GIS) and a Cartesian nano-robotic manipulator (Klocke Nanotechnik GmbH, Aachen, Germany).…”

“…In order to calculate the theoretical electron diffraction profiles, we used data from JEMS software [30]. The structural parameters of g-Al 2 O 3 and d*-Al 2 O 3 are also based on the papers published in the literature [18,28].…”

Surface contacts strongly influence the elasticity and thermal conductivity of silica nanoparticle fibers

“…Prior to the discussion of the elastic moduli of the fibers and understanding the origin of its elastic enhancements, the knowledge of the elastic properties of the constituent silica NPs is a prerequisite. Experimental access to the elasticity of NPs and their assembled structure simultaneously by BLS is for the first time reported in the granular materials 5,7,17,18 . It is well established that NPs exhibit vibrations, in analogy to the electron motion in atoms.…”

“…The different responses of r b and r a to loading leads to a decoupling of k n and k s in Equation 2. Digby model has adequately described sintered systems such as poly(methyl methacrylate) NPs 34 but failed for other systems like titanium dioxide NPs 18 .…”

Mechanical Properties of Nanoporous Metallic Ultrathin Films: A Paradigmatic Case

“…We pinpoint that a typical displacement involved in picosecond photoacoustic experiments is in the range of 1 to 10 pm (depending on the exploited pump pulse energy) for thicknesses in the order of 10 nm, thus resulting in a strain in the order of 10 −3 -10 −4 . Hence, in its various forms, photoacoustic nanometrology is emerging as the go-to technique for the inspection of thin-film [39,[49][50][51][52][53][54], ultrathin film [37,[39][40][41][42][43], and nanoparticle [55,56] mechanics, and the topic is in rapid and continuous evolution. Cross-feed from other topical areas has recently resulted in novel inspection protocols based on the photoacoustic effects.…”