Atomistic Mismatch Defines Energy–Structure Relationships during Oriented Attachment of Nanoparticles

Abstract

Oriented attachment is an important crystal growth pathway in nature and has been extensively exploited to develop hierarchically structured crystalline materials. Atomistic mismatch in the crystal structure of two particles in the solvent-separated state creates forces that drive particle motions enabling solvent expulsion and coalescence, but the relative magnitudes of the energy barriers for approach, rotation, and translation are not well-known. Here we use classical molecular simulations to calculate the potential of mean force for these three different motions for basal surface encounters of gibbsite nanoplatelets separated by one water layer. In all cases, the highest energy barrier is associated with removing this last water layer to enable jump to contact, even when coaligned. Mutual rotation is more probable than sliding motion, which are both much more probable than jump to contact. This work provides the first comparison on an equal footing of the energy–structure relationships for multiple alignment paths between solvent-separated particles in bulk aqueous solution.

Effects of Size and Shape on the Tolerances for Misalignment and Probabilities for Successful Oriented Attachment of Nanoparticles

“…The ability of our simple model to predict the basic properties of a rotational energy landscape is supported by comparison to a recent molecular dynamics study by Ho et al that was published shortly after our paper was submitted for review. They calculated rotational energy landscapes for hexagonal gibbsite platelets with a d/w ratio of 1/8.…”

“…Similar ideas have also been suggested in the context of OA for protein crystals, where larger crystals with higher contact areas (and hence larger interparticle forces) were found to have a higher probably of attaching in improper translational alignments, thus making it important to fine-tune interparticle forces to maximize OA assembly. 28 The ability of our simple model to predict the basic properties of a rotational energy landscape is supported by comparison to a recent molecular dynamics study by Ho et al 33 that was published shortly after our paper was submitted for review. They calculated rotational energy landscapes for hexagonal gibbsite platelets with a d/w ratio of 1/8.…”

“…However, in practice, particles may continue to slip or twist relative to each other, sampling different orientations until they find a configuration that is more suitable for OA, particularly if they retain a layer of lubricating solvent between their faces. Sophisticated experiments and molecular modeling indicate that a wide diversity of forces may define complex orientation-dependent energy landscapes. − ,− For example, some systems appear to possess long-range dipole forces and dispersion forces that may guide alignment prior to close contact, , while others do not. However, it is beyond the scope of this paper to address the full diversity of interfacial forces that may exist between real-world particles.…”

Roles of Hydrogen Bonds and Alignment in Oriented Attachment of Gibbsite Nanoparticles: Insights from Molecular Dynamics

“…On the gibbsite basal surface (i.e., looking down the c -axis of the gibbsite lattice), the Al–O bonding network forms a system of unit hexagons, as shown in Figure a (also see Figure in our previous work) . We define the particle/slab misalignment as normalM normali normals normala normall normali normalg normaln normalm normale normaln normalt = 1 − ∑ 1 n C i / A i n where C i is the overlapped surface area between the unit hexagon A i of the particle and the unit hexagon B i of the slab ( A i = B i , Figure a).…”

“…The initial configuration of the 1W case is obtained directly from the end of the equilibrium simulation. To obtain the 2W configuration (Figure d), the particle in Figure c is pulled up along the z -direction to the distance established as the 2W minimum in the previous study . The temperature is 300 K.…”