Direction-specific van der Waals attraction between rutile TiO2 nanocrystals

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Science  28 Apr 2017:
Vol. 356, Issue 6336, pp. 434-437
DOI: 10.1126/science.aah6902

When forces depend on orientation

In oriented attachment, small nuclei or crystals come together to make a larger crystal, but only when complementary facets approach each other. Does this mean that there is an orientational dependence of the force between two nanocrystals? Zhang et al. report a delicate method to measure the van der Waals attraction between rutile TiO2 nanocrystals. They imaged the contact point in situ with environmental transmission electron microscopy, which allowed the interparticle distances to be measured accurately. This elucidated the relationship between the nanocrystals' orientations, surface hydrations, and interactions. The results suggest that there is enough force to generate a torque between the crystals to ensure a complementary interaction.

Science, this issue p. 434