Abstract
Crystal architectures delimited by sinuous boundaries and exhibiting complex hierarchical structures are a common product of natural biomineralization. However, related forms can also be generated in purely inorg. environments, as exemplified by the existence of so-called "silica-carbonate biomorphs". These peculiar objects form upon copptn. of barium carbonate with silica and self-assemble ...
Abstract
Crystal architectures delimited by sinuous boundaries and exhibiting complex hierarchical structures are a common product of natural biomineralization. However, related forms can also be generated in purely inorg. environments, as exemplified by the existence of so-called "silica-carbonate biomorphs". These peculiar objects form upon copptn. of barium carbonate with silica and self-assemble into aggregates of highly oriented, uniform nanocrystals, displaying intricate noncrystallog. morphologies such as flat sheets and helicoidal filaments. While the driving force steering ordered mineralization on the nanoscale has recently been identified, the factors governing the development of curved forms on global scales are still inadequately understood. The authors have studied the circumstances that lead to the expression of smooth curvature in these systems and propose a scenario that may explain the obsd. morphologies. Detailed studies of the growth behavior show that morphogenesis takes crucial advantage of reduced nucleation barriers at both extrinsic and intrinsic surfaces. That is, sheets grow in a quasi-two-dimensional fashion because they spread across interfaces such as walls or the soln. surface. In turn, twisted forms emerge when there is no foreign surface to grow on, such that the evolving aggregates curve back on themselves to use their own as a substrate. These hypotheses are corroborated by expts. with micropatterned surfaces, which show that the morphol. selection intimately depends on the topol. of the offered substrate. Finally, with the aid of suitable template patterns, it is possible to directly mold the shape (and size) of silica biomorphs and thus gain polycryst. materials with predefined morphologies and complex structures.
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