| Experimental studies have shown that nanoparticle chain aggregates, made of various materials, can be strained up to 100%; after breaking they contract to more compact structures. Using atomistic computer simulations, the behavior of small copper nanoparticle aggregates under strain is investigated and force estimates obtained. The copper interatomic interaction potential is obtained with the embedded atom method.; In the first part of this work, a 675 atom nanoparticle is melted and subsequently solidified at various cooling rates. The lowest cooling rate gives the lowest potential energy nanoparticle, which is a face-centered cubic polyhedron similar to an hexakaiicosahedron. Next, two to seven identical hexakaiicosahedra are sintered at 300 K in various aggregate configurations. Interparticle bond energies defined (for the first time) and calculated for the sintered aggregates vary from about 21 eV to 42 eV depending on the initial contact direction and the number of primary particles per aggregate. The bond energies are compared with macroscale particle adhesion theory predictions.; Finally, aggregates are strained to breaking using molecular dynamics and energy minimization straining. Two seven nanoparticle aggregates are studied, one linear and the other kinked. The linear aggregate yield strain is about 0.1. The kinked aggregate elastic limit is also about 0.1, but only one third of the stress develops compared to the linear aggregate. The kinked aggregate breaks at a strain of about 0.5, five times higher than the breaking strain of the linear aggregate. The ability of the kinked aggregate to straighten through combined nanoparticle interface sliding and rotation accounts for the extra strain accommodation. Sudden strain unloading leads to plastic deformation in both linear and kinked aggregates.; Although simulation strain rates are orders of magnitude higher than previous experimental observations, simulated straining at different rates has little effect on aggregate behavior. That is, over certain ranges, aggregate behavior is independent of strain rates. Applications of the experimental and simulation studies are to the behavior of nanocomposite materials, sampling of aggregates by high-speed impactors and the formation of flexible coatings of nanoparticles. Atomistic simulations can also serve as models with which to compare predictions of theories based on macroscale concepts. |
