Cement nanotubes: on chemical gardens and cement

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.

Growth of chemical gardens in gaseous acidic atmospheres

The generation of chemobrionic architectures through slow injection of aqueous silicate solution in gaseous TiCl₄ is demonstrated. The tubes were characterized by XRD, SEM and wet chemistry control experiments, and their mechanism of formation was unraveled. These structures serve as laboratory models for calthemites or soda straws.

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.

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.

Dynamic diffusion and precipitation processes across calcium silicate membranes

HYPOTHESIS

Chemical gardens are tubular inorganic structures exhibiting complex morphologies and interesting dynamic properties upon ageing, with coupled diffusion and precipitation processes keeping the systems out of equilibrium for extended periods of time. Calcium-based silica gardens should comprise membranes that mimic the microstructures occurring in ordinary Portland cement and/or silicate gel layers observed around highly reactive siliceous aggregates in concrete.

EXPERIMENTS

Single macroscopic silica garden tubes were prepared using pellets of calcium chloride and sodium silicate solution. The composition of the mineralized tubes was characterized by means of various ex-situ techniques, while time-dependent monitoring of the solutions enclosed by and surrounding the membrane gives insight into the spatiotemporal distribution of the different ionic species. The latter data reflect transport properties and precipitation reactions in the system, thus allowing its complex dynamic behavior to be resolved.

FINDINGS

The results show that in contrast to the previously studied cases of iron- and cobalt-based silica gardens, the formed calcium silicate membrane is homogeneous and ultimately becomes impermeable to all species except water, hydroxide and sodium ions, resulting in the permanent conservation of considerable concentration gradients across the membrane. The insights gained in this work may help elucidate the nature and mechanisms of ion diffusion in Portland cements and concrete, especially those occurring during initial hydration of calcium silicates and the so-called alkali-silica reaction (ASR), one of the major concrete deterioration mechanisms causing serious problems with respect to the durability of concrete and the restricted use of many potential sources of raw materials.

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...

Chemobrionics: From Self-Assembled Material Architectures to the Origin of Life

Self-organizing precipitation processes, such as chemical gardens forming biomimetic micro- and nanotubular forms, have the potential to show us new fundamental science to explore, quantify, and understand nonequilibrium physicochemical systems, and shed light on the conditions for life's emergence. The physics and chemistry of these phenomena, due to the assembly of material architectures under a flux of ions, and their exploitation in applications, have recently been termed chemobrionics. Advances in understanding in this area require a combination of expertise in physics, chemistry, mathematical modeling, biology, and nanoengineering, as well as in complex systems and nonlinear and materials sciences, giving rise to this new synergistic discipline of chemobrionics.

Precipitation patterns driven by gravity current

A precipitation reaction can be driven by a gravity current that spreads on the bottom as a denser fluid is injected into an initially stagnant liquid. Supersaturation and nucleation are restricted to locations where the two liquids come into contact; hence, the flow pattern governs the spatial distribution of the final product. In this numerical study, we quantitatively characterize the flow associated with the gravity current prior to the onset of nucleation and distinguish three zones where the coupling of transport processes with the reaction can take place depending on their time scales. A scaling law associated with the region of Rayleigh-Taylor instability behind the tip of the gravity current is also determined.

Self-Assembling Ice Membranes on Europa: Brinicle Properties, Field Examples, and Possible Energetic Systems in Icy Ocean Worlds

Brinicles are self-assembling tubular ice membrane structures, centimeters to meters in length, found beneath sea ice in the polar regions of Earth. We discuss how the properties of brinicles make them of possible importance for chemistry in cold environments-including that of life's emergence-and we consider their formation in icy ocean worlds. We argue that the non-ice composition of the ice on Europa and Enceladus will vary spatially due to thermodynamic and mechanical properties that serve to separate and fractionate brines and solid materials. The specifics of the composition and dynamics of both the ice and the ocean in these worlds remain poorly constrained. We demonstrate through calculations using FREZCHEM that sulfate likely fractionates out of accreting ice in Europa and Enceladus, and thus that an exogenous origin of sulfate observed on Europa's surface need not preclude additional endogenous sulfate in Europa's ocean. We suggest that, like hydrothermal vents on Earth, brinicles in icy ocean worlds constitute ideal places where ecosystems of organisms might be found.

Exploding Chemical Gardens: A Phase-Change Clock Reaction

Chemical gardens and clock reactions are two of the best-known demonstration reactions in chemistry. Until now these have been separate categories. We have discovered that a chemical garden confined to two dimensions is a clock reaction involving a phase change, so that after a reproducible and controllable induction period it explodes.

Macroscale precipitation kinetics: towards complex precipitate structure design

Producing self-assembled inorganic precipitate micro- and macro-structures with tailored properties may pave the way for new possibilities in, e.g., materials science and the pharmaceutical industry.