Oriented attachment (OA) of nanoparticles is an important crystal growth pathway. The role of the nanoparticles, solvent, and their interactions during particle alignment remain unclear. We perform molecular dynamics (MD) simulations to calculate the potential of mean force (PMF) profile for a gibbsite particle sliding across a gibbsite slab where the slab and particle are separated by one or two water layers (1W or 2W). The gibbsite surfaces and the water between them are analyzed to determine how the number and type of hydrogen bonds (H-bonds) influence the free energy profile during alignment. The PMF profile exhibits a periodicity of length 5.078 Å, consistent with the gibbsite unit cell size along the b-axis. In both 1W and 2W cases, the lowest energy state is found when the particle and slab are fully aligned because these configurations contain the largest number of H-bonds between both (a) the surface -OH groups and interlayer water and (b) water molecules. The energy barrier for particle-slab alignment is larger for the 1W than the 2W case. The 1W PMF profile exhibits a local free energy minimum between two aligned configurations, suggesting that imperfectly aligned attachment may occur. The energetic analyses suggest that in a fully aligned configuration, the large negative enthalpy contribution results in a global free energy minimum. In order to describe configurations that are not fully aligned, we quantified the degree of mismatch between the particle and the slab. The mismatch profile exhibits a strong correlation with the PMF profile for the 2W case. These analyses help explain the roles of surface interaction and confined water to particle alignment prior to the “jump-to-contact” in oriented attachment.

Energetic and structural transformation during the alignment stage of oriented attachment of gibbsite nanoparticles

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