Several theories or models have been proposed to account for the biofabrication of the architecture of nacre layers in mollusk shell; among them, a dipole-driven self-assembly mineralization model has been put forward to account for the oriented alignment of aragonite nanocrystals in an aragonite tablet and the formation of local co-oriented aragonite columns in nacre. In order to test the dipole-driven self-assembly model, we select witherite, which is isostructural with aragonite, as a model mineral to examine the concept. Herein, nanoscale witherite rods (nanorods) were first synthesized by use of dimethyl sulfoxide (DMSO) as a stabilizer, and then the completely washed up nanorods were redispersed in deionized water to obtain organized mesoscale witherite rods (mesocrystals or mesorods) at ambient temperature. The nano- or mesorods obtained under different conditions were characterized by a range of techniques involving XRD, FTIR, FESEM, TEM, SAED, and HRTEM. The SEM, TEM and SAED results demonstrate that the witherite nanorods can be spontaneously organized into mesorods in deionized water at ambient temperature via an oriented-attachment growth process, indicating that the intrinsic anisotropic dipole-dipole interactions between the assembled nanorods should be responsible for the self-assembly of the nanorods into the mesorods of witherite. Therefore, our results can provide a direct examination for dipole driven self-assembly, and show that dipole-dipole interactions can reasonably account for some aspects of the formation of hierarchical biominerals.

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