Additive-induced morphological tuning of
self-assembled silica-barium carbonate crystal aggregates,
Crystn. of barium carbonate from alk. silica solns. results in the formation of
extraordinary micron-scale architectures exhibiting non-crystallog. curved
shapes, such as helical filaments and worm-like braids. These so-called
"silica biomorphs" consist of a textured assembly of uniform
elongated witherite nanocrystallites, which is occasionally sheathed by a skin
of amorphous silica. Although great efforts have been devoted to clarifying the
phys. origin of these fascinating materials, to date little is known about the
processes underlying the obsd. self-organization. Herein, we describe the
effect of two selected additives, a cationic surfactant and a cationic polymer,
on the morphol. of the forming crystal aggregates, and relate changes to expts.
conducted in the absence of additives. Minor amts. of both substances are shown
to exert a significant influence on the growth process, leading to the
formation of predominantly flower-like spherulitic aggregates. The obsd.
effects are discussed in terms of feasible morphogenesis pathways. Based on the
assumption of a template membrane steering biomorph formation, it is proposed
that the two additives are capable of performing specific bridging functions
promoting the aggregation of colloidal silica which constitutes the membrane.
Morphol. changes are tentatively ascribed to varying colloid coordination
effecting distinct membrane curvatures.
Matthias Kellermeier, Fabian Glaab, Anna M. Carnerup, Markus Drechsler,
Benjamin Gossler, Stephen T. Hyde, and Werner Kunz,
Journal of Crystal Growth 311(8) (2009), 2530-2541.