Eshelby untwisting

XD Zhong and HY Zhou and C Li and AG Shtukenberg and MD Ward and B Kahr, CHEMICAL COMMUNICATIONS, 57, 5538-5541 (2021).

DOI: 10.1039/d1cc01431e

The concept of Eshelby untwisting, the effect of an axial screw dislocation driving an intrinsically twisted nanocrystal towards a straighter configuration more consistent with long-range translational symmetry, is introduced here. Force-field simulations of nanorods built from the enantiomorphous (space groups, P3(1)21 and P3(2)21) crystal structures of benzil (C6H5-C(O)-C(O)-C6H5) were previously shown to twist in opposite directions, even in the absence of dislocations. Here, both right- and left-handed screw dislocations were introduced into benzil nanorods in silico. For rods built from the P3(2)21 enantiomorph, dislocations with negative Burgers vectors increased the right-handed twisting already present in the intrinsically twisted structures without dislocations, whereas dislocations with positive Burgers vectors drove the twisted structure back towards a straight configuration, untwisting. In the dynamic simulations, the P3(2)21 helicoid endowed with a positive Burgers vector ultimately twisted back through the straight configuration, until a helicoid of opposite sense from that of the starting structure, was obtained. The bearing of these observations on the propensity of small crystals to adopt non-polyhedral morphologies is discussed.

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