2 research outputs found
Interdependent Roles of Electrostatics and Surface Functionalization on the Adhesion Strengths of Nanodiamonds to Gold in Aqueous Environments Revealed by Molecular Dynamics Simulations
Molecular dynamics
simulations demonstrate that adhesion strengths
as a function of charge for aqueous nanodiamonds (NDs) interacting
with a gold substrate result from an interdependence of electrostatics
and surface functionalization. The simulations reveal a water layer
containing Na<sup>+</sup> counterions between a negative ND with surface
−COO<sup>–</sup> functional groups that is not present
for a positively charged ND with −NH<sub>3</sub><sup>+</sup> functional groups. The closer proximity of the positive ND to the
gold surface and the lack of cancelation of electrostatic interactions
due to counterions and the water layer lead to an electrostatic adhesion
force for the positive ND that is nearly three times larger than that
of the negative ND. Prior interpretations of experimental tribological
studies of ND–gold systems suggested that electrostatics or
surface functionalization could be responsible for observed adhesion
strength differences. The present work demonstrates how these two
effects work together in determining adhesion for this system
New Method for Extracting Diffusion-Controlled Kinetics from Differential Scanning Calorimetry: Application to Energetic Nanostructures
A new expression is derived for interpreting
differential scanning
calorimetry curves for solid-state reactions with diffusion-controlled
kinetics. The new form yields an analytic expression for temperature
at the maximum peak height that is similar to a Kissinger analysis,
but that explicitly accounts for laminar, cylindrical, and spherical
multilayer system geometries. This expression was used to analyze
two reactive multilayer nanolaminate systems, a Zr/CuO thermite and
an Ni/Al aluminide, that include systematically varied layer thicknesses.
This new analysis scales differential scanning calorimetry (DSC) peak
temperatures against sample geometry, which leads to geometry-independent
inherent activation energies and prefactors. For the Zr/CuO system,
the DSC data scale with the square of the bilayer thickness, while,
for the Ni/Al system, the DSC data scale with the thickness. This
suggests distinct reaction mechanisms between these systems