DISCOVERIES REGARDING GIBBSITE NANOPARTICLE BEHAVIOR USING MOLECULAR SIMULATION

Using gibbsite and classical molecular dynamics simulations, we have investigated the processes of particle compaction, ion adsorption, oriented attachment, and epitaxial growth between gibbsite nanoparticles and a large corundum crystal surface. The rate of water removal plays a key role in the nature of the porous media created due to particle compaction. The slower the water removal, the more likely the clay-like particles will assemble basal-surface to basal-surface, forming a nicely stacked nano-rock with low porosity and pore-size distribution. Potential of mean force (PMF) calculations demonstrate that the attachment of two gibbsite particles through their basal surfaces is energetically preferred over edge-edge or edge-basal surface attachment. These simulations reinforce the concept that slow water evaporation will allow time for equilibration between the particles and lead to more layered shale-like features. They also provide insight into oriented-particle attachment as a non-classical crystal growth mechanism. The highest energy barrier to particle-particle attachment involves the removal of the final monolayer of water between the particles, allowing them to jump into contact. Atom-by-atom mismatch between the crystal structure of two particles in this solvent-separated state creates forces that drive particle motions enabling solvent expulsion and coalescence. We further investigate this state using PMF calculations to study particle rotation and translation while separated by one water layer. Initial investigations of gibbsite nanoparticle adsorption onto a larger corundum surface suggest that at the nanoscale, the minor differences in the gibbsite and corundum surface structure can greatly complicate the energy profile for monolayer nanoparticle attachment.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-9784 A.