Filament dynamics in planar chemical gardens

Precipitation-induced filament pattern of injected fluid controlled by a structured cell

Mixing of two fluids can lead to the formation of a precipitate. If one of the fluids is injected into a confined space filled with the other, then a created precipitate disrupts the flow locally and forms complex spatiotemporal patterns. The relevance of controlling these patterns has been highlighted in the engineering and geological contexts. Here, we show that such injection patterns can be controlled consistently by injection rate and obstacles. Our experimental results revealed filament patterns for high-injection and low-reaction rates, and the injection rate can control the number of active filaments. Furthermore, appropriately spaced obstacles in the cells can straighten the motion of the advancing tip of the filament. A mathematical model based on a moving boundary adopting the effect of precipitation reproduced the phase diagram and the straight motion of filaments in structured cells. Our study clarifies the impact of the nonlinear permeability response on the precipitate density and that of the obstacles in the surrounding medium on the motion of the injected fluid with precipitation.

Light-modulated colour transformation in highly intertwined vertically growing silver tungstate tubes

Achieving control over growth kinetics in chemical garden architectures is challenging due to the nonequilibrium conditions. In this study, we demonstrate the vertical growth of silver tungstate chemical garden tubes under both illuminated and dark conditions, a phenomenon not observed in a comparable silver-based system, specifically silver silicate, under light exposure. Physicochemical factors, viz. thermo chemical radius of the tungstate anion, its density-buoyancy relation, the osmotic pressure gradient, and the hydration enthalpy, contributed to the tube appearance in silver tungstate even in light. Tubes grown in light illumination were greyish black, while dark-grown tubes were creamy white, and both tubes appeared twisted and highly intertwined. The colour of the as obtained silver tungstate tubes could be transformed via exposure to light. In the presence of a strong oxidizing agent, the growing tubes retain the original creamy white colour even under illumination. Colour transformation in chemical garden tubes has not yet been observed, and this report could lead the way.

Pattern selection by material aging: Modeling chemical gardens in two and three dimensions

Chemical gardens are complex, often macroscopic, structures formed by precipitation reactions. Their thin walls compartmentalize the system and adjust in size and shape if the volume of the interior reactant solution is increased by osmosis or active injection. Spatial confinement to a thin layer is known to result in various patterns including self-extending filaments and flower-like patterns organized around a continuous, expanding front. Here, we describe a cellular automaton model for this type of self-organization, in which each lattice site is occupied by one of the two reactants or the precipitate. Reactant injection causes the random replacement of precipitate and generates an expanding near-circular precipitate front. If this process includes an age bias favoring the replacement of fresh precipitate, thin-walled filaments arise and grow-like in the experiments-at the leading tip. In addition, the inclusion of a buoyancy effect allows the model to capture various branched and unbranched chemical garden shapes in two and three dimensions. Our results provide a model of chemical garden structures and highlight the importance of temporal changes in the self-healing membrane material.

Dissimilar chemobrionic growth in copper silicate chemical gardens in the absence or presence of light

The effect of the absence of light on chemical garden growth has been neglected although the gardens resemble hydrothermal vents that grow in dark in the sea/ocean. Herein, we report the differential growth of chemobrionic structures in copper silicate when identical reactions to yield copper silicate chemical gardens were carried out in the presence or absence of light. Irradiating the copper silicate chemical garden during its growth with different wavelengths of light independently resulted in morphologically divergent tubes.

Downward fingering accompanies upward tube growth in a chemical garden grown in a vertical confined geometry

Chemical gardens are self-assembled structures of mineral precipitates enabled by semi-permeable membranes. To explore the effects of gravity on the formation of chemical gardens, we have studied chemical gardens grown from cobalt chloride pellets and aqueous sodium silicate solution in a vertical Hele-Shaw cell. Through photography, we have observed and quantitatively analysed upward growing tubes and downward growing fingers. The latter were not seen in previous experimental studies involving similar physicochemical systems in 3-dimensional or horizontal confined geometry. To better understand the results, further studies of flow patterns, buoyancy forces, and growth dynamics under schlieren optics have been carried out, together with characterisation of the precipitates with scanning electron microscopy and X-ray diffractometry. In addition to an ascending flow and the resulting precipitation of tubular filaments, a previously not reported descending flow has been observed which, under some conditions, is accompanied by precipitation of solid fingering structures. We conclude that the physics of both the ascending and descending flows are shaped by buoyancy, together with osmosis and chemical reaction. The existence of the descending flow might highlight a limitation in current experimental methods for growing chemical gardens under gravity, where seeds are typically not suspended in the middle of the solution and are confined by the bottom of the vessel.

Archimedean Spirals Form at Low Flow Rates in Confined Chemical Gardens

We describe and study the formation of confined chemical garden patterns. At low flow rates of injection of cobalt chloride solution into a Hele-Shaw cell filled with sodium silicate, the precipitate forms with a thin filament wrapping around an expanding "candy floss" structure. The result is the formation of an Archimedean spiral structure. We model the growth of the structure mathematically. We estimate the effective density of the precipitate and calculate the membrane permeability. We set the results within the context of recent experimental and modeling work on confined chemical garden filaments.

Filament dynamics in vertical confined chemical gardens

When confined to a Hele-Shaw cell, chemical gardens can grow as filaments, narrow structures with an erratic and tortuous trajectory. In this work, the methodology applied to studies with horizontal Hele-Shaw cells is adapted to a vertical configuration, thus introducing the effect of buoyancy into the system. The motion of a single filament tip is modeled by taking into account its internal pressure and the variation of the concentration of precipitate that constitutes the chemical garden membrane. While the model shows good agreement with the results, it also suggests that the concentration of the host solution of sodium silicate also plays a role in the growth of the structures despite being in stoichiometric excess.

Formation and growth of lithium phosphate chemical gardens

We show that a chemical garden can be developed from an alkaline metal precipitate using a flow-driven setup. By injecting sodium phosphate solution into lithium chloride solution from below, a liquid jet appears, on which a precipitate grows forming a structure resembling a hydrothermal vent. The precipitate column continuously builds upward until a maximum height is reached. The vertical growth then significantly slows down while the tube diameter still increases. The analysis of the growth profiles has revealed a linear dependence of volume growth rate on the injection rate, hence yielding a universal growth profile. The expansion in diameter, localized at the tip of the structure, scales with a power law suggesting that the phenomenon is controlled by both diffusion and convection.

Dark–induced vertical growth of chemobrionic architectures in silver based precipitating chemical gardens

Light sensitivity of many silver compounds has restricted observation of silver based chemical gardens. Here we report for the first time, silver based chemical gardens grown in dark. An identical...