Crystal growth by assembly of small particles or clusters as opposed to ion-by-ion is a recently recognized type of growth impacting our understanding of natural mineralization processes, and holding promise for novel materials design. Oriented aggregation is an important case where larger crystals grow by the oriented self-assembly of smaller ones, typically nanoparticles. Successful attachment is predicated upon near-perfect co-alignment prior to expulsion of thin layers of intervening solvent and coalescence. In this metastable solvent-separated state, as mutual orientations are randomly sampled and when nearly co-aligned the presence of an interparticle torque that favors rotation into alignment is implied but remains poorly quantified. Only in recent <i>in situ</i> liquid-cell transmission electron microscopy (TEM) measurements was it shown that the rotation of ferrihydrite particles accelerates when they are nearly co-aligned, while still separated by a nanometer of solution. Here we demonstrate direction-specific interaction force between nanocrystals under precise control of distance, mutual orientation, and surface hydration extent. At tens of nanometers of separation the attraction is weak and shows no dependence on azimuthal alignment nor surface hydration.  In attractive contact, the force strongly depends on azimuthal alignment, and systematically decreases as adsorbed water density increases. Measured forces are in comprehensive agreement with predictions from Lifshitz theory, and contribute to the understanding of forces capable of generating a torque between particles interacting in solution and grains in materials. <br/>

Direction-Specific interaction force between nanocrystals

253rd National Meeting (2017)

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