The emergence of complex nano- and microstructures is of fundamental interest, and the ability to program their form has practical ramifications in fields such as optics, catalysis, and electronics. We developed carbonate-silica microstructures in a dynamic reaction-diffusion system that allow us to rationally devise schemes for precisely sculpting a great variety of elementary shapes by diffusion of carbon dioxide (CO2) in a solution of barium chloride and sodium metasilicate. We identify two distinct growth modes and show how continuous and discrete modulations in CO2 concentration, pH, and temperature can be used to deterministically switch between different regimes and create a bouquet of hierarchically assembled multiscale microstructures with unprecedented levels of complexity and precision. These results outline a nanotechnology strategy for "collaborating" with self-assembly processes in real time to build arbitrary tectonic architectures.
We thank J. C. Weaver for advice with the SEM imaging, S. K. Y. Tang and R. Sadza for the microfluidic experiments, L. Hendriks for growing the structures in Fig. 5F, and A. J. Aizenberg for help with the manuscript. This work was supported by the NSF Materials Research Science and Engineering Centers under award no. DMR-0820484. W.L.N. thanks the Netherlands Organization for Scientific Research for financial support. EM was performed at Harvard’s Center for Nanoscale Systems, supported by the NSF under award no. ECS-0335765.