Biomorph Oscillations Self-organize Micrometer-Scale Patterns and Nanorod Alignment Waves

Abstract

The coprecipitation of barium carbonate and silica spontaneously creates complex micrometer-scale objects such as sheets and helices. These structures consist of densely packed crystalline nanorods that in the case of sheets align in radial direction. We report the existence of an additional level of self-organization that creates oscillatory height variations in biomorph sheets. These topographic features take the form of either concentric rings or disordered, patchy patterns and form immediately in the wake of the crystallization front. Their wavelength varies around 6.5 μm and shows no pronounced dependence on the reactant concentrations. Atomic force microscopy reveals height variations of up to 500 nm which equal 45% of the average sheet thickness. These undulations are accompanied by a systematic out-of-plane displacement of the nanorods. Our results are discussed in the context of an earlier hypothesis that predicts pH oscillations near the crystallization front.

Authigenesis of biomorphic apatite particles from Benguela upwelling zone sediments off Namibia: The role of organic matter in sedimentary apatite nucleation and growth

“…The outer layers of the rod‐shaped particles appear wider, possibly due to a geometric effect of the cross‐sections cutting through the ellipsoidal rod‐shaped particles at different distances with respect to their centre ( e.g ., Cosmidis et al., ). Similar nanometre scale autocatalytic self‐organization of the precipitates, due to oscillations in the local microenvironment, is known in silica‐carbonate biomorphs ( e.g ., Nakouzi, Ghoussoub, Knoll, & Steinbock, ), and can result in the formation of intrinsic mineralized banding patterns with the same periodicity (Montalti et al., ). Therefore, such layering observed in rod‐shaped apatite particles could be the result of alternating levels of phosphate input, in turn, a result of intermittent microbial phosphate pumping by polyphosphate‐accumulating bacteria (Jones, Flood, & Bailey, ; Schulz & Schulz, ).…”

Inorganic Reactions Self‐organize Life‐like Microstructures Far from Equilibrium

“…Most of the planar structures start from a globule on the reactor substrate and then grow on that surface radially outwards at speeds of a fraction of to a few micrometers per minute (Figure a) ,. These sheets can be surprisingly circular, but typically experience disruptions of the growth front.…”

“…In shallow solution layers, the typical pH ranges from 10 to 11 for this procedure and produces worms, double helices, and leaves. [10,16,24] However, in deeper containers and at higher barium concentrations, the pH can be extended to values of up to 11.8 producing stemmed flowers and coral-like shapes. [25] Noorduin et al demonstrated that temporary increases of the ambient CO 2 pressure (by opening and closing of the lid) induce thickened rings around the growing structures due to the faster formation of barium carbonate crystals.…”

“…also measured elemental maps using EDX spectroscopy which showed spatial bands in the Ba : Si ratio, although similar measurements by Nakouzi et al. revealed no compositional changes ,…”

“…Most of the planar structures start from a globule on the reactor substrate and then grow on that surface radially outwards at speeds of a fraction of to a few micrometers per minute (Figure 3a). [15][16]41] These sheets can be surprisingly circular, but typically experience disruptions of the growth front. These disruptions trigger the formation of stationary edges that tangentially expand along the forward moving front to yield planar, leaf-like objects or star-shaped sheets if multiple front breaks occur.…”