Mechanical strength of amorphous CaCO3 colloidal spheres

Uncovering the Dynamics of Urease and Carbonic Anhydrase Genes in Ureolysis, Carbon Dioxide Hydration, and Calcium Carbonate Precipitation

The hydration of CO2 suffers from kinetic inefficiencies that make its natural trapping impractically sluggish. However, CO2-fixing carbonic anhydrases (CAs) remarkably accelerate its equilibration by 6 orders of magnitude and are, therefore, "ideal" catalysts. Notably, CA has been detected in ureolytic bacteria, suggesting its potential involvement in microbially induced carbonate precipitation (MICP), yet the dynamics of the urease (Ur) and CA genes remain poorly understood. Here, through the use of the ureolytic bacteriumSporosarcina pasteurii, we investigate the differing role of Ur and CA in ureolysis, CO2 hydration, and CaCO3 precipitation with increasing CO2(g) concentrations. We show that Ur gene up-regulation coincides with an increase in [HCO3-] following the hydration of CO2 to HCO3- by CA. Hence, CA physiologically promotes buffering, which enhances solubility trapping and affects the phase of the CaCO3 mineral formed. Understanding the role of CO2 hydration on the performance of ureolysis and CaCO3 precipitation provides essential new insights, required for the development of next-generation biocatalyzed CO2 trapping technologies.

Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach

Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny–Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface.

Matrix-induced pre-strain and mineralization-dependent interfibrillar shear transfer enable 3D fibrillar deformation in a biogenic armour

The cuticle of stomatopod is an example of a natural mineralized biomaterial, consisting of chitin, amorphous calcium carbonate and protein components with a multiscale hierarchical structure, and forms a protective shell with high impact resistance. At the ultrastructural level, cuticle mechanical functionality is enabled by the nanoscale architecture, wherein chitin fibrils are in intimate association with enveloping mineral and proteins. However, the interactions between these ultrastructural building blocks, and their coupled response to applied load, remain unclear. Here, we elucidate these interactions via synchrotron microbeam wide-angle X-ray diffraction combined with in situ tensile loading, to quantify the chitin crystallite structure of native cuticle - and after demineralization and deproteinization - as well as time-resolved changes in chitin fibril strain on macroscopic loading. We demonstrate chitin crystallite stabilization by mineral, seen via a compressive pre-strain of approximately 0.10% (chitin/protein fibre pre-stress of ∼20 MPa), which is lost on demineralization. Clear reductions of stiffness at the fibrillar-level following matrix digestion are linked to the change in the protein/matrix mechanical properties. Furthermore, both demineralization and deproteinization alter the 3D-pattern of deformation of the fibrillar network, with a non-symmetrical angular fibril strain induced by the chemical modifications, associated with loss of the load-transferring interfibrillar matrix. Our results demonstrate and quantify the critical role of interactions at the nanoscale (between chitin-protein and chitin-mineral) in enabling the molecular conformation and outstanding mechanical properties of cuticle, which will inform future design of hierarchical bioinspired composites. STATEMENT OF SIGNIFICANCE: Chitinous biomaterials (e.g. arthropod cuticle) are widespread in nature and attracting attention for bioinspired design due to high impact resistance coupled with light weight. However, how the nanoscale interactions of the molecular building blocks - alpha-chitin, protein and calcium carbonate mineral - lead to these material properties is not clear. Here we used X-ray scattering to determine the cooperative interactions between chitin fibrils, protein matrix and biominerals, during tissue loading. We find that the chitin crystallite structure is stabilized by mineral nanoparticles, the protein phase prestresses chitin fibrils, and that chemical modification of the interfibrillar matrix significantly disrupts 2D mechanics of the microfibrillar chitin plywood network. These results will aid rational design of advanced chitin-based biomaterials with high impact resistance.

Temperature-induced amorphization in CaCO3 at high pressure and implications for recycled CaCO3 in subduction zones

Calcium carbonate (CaCO₃) significantly affects the properties of upper mantle and plays a key role in deep carbon recycling. However, its phase relations above 3 GPa and 1000 K are controversial. Here we report a reversible temperature-induced aragonite-amorphization transition in CaCO₃ at 3.9-7.5 GPa and temperature above 1000 K. Amorphous CaCO₃ shares a similar structure as liquid CaCO₃ but with much larger C-O and Ca-Ca bond lengths, indicating a lower density and a mechanism of lattice collapse for the temperature-induced amorphous phase. The less dense amorphous phase compared with the liquid provides an explanation for the observed CaCO₃ melting curve overturn at about 6 GPa. Amorphous CaCO₃ is stable at subduction zone conditions and could aid the recycling of carbon to the surface.

Quantifying Rock Weakening Due to Decreasing Calcite Mineral Content by Numerical Simulations

The quantification of changes in geomechanical properties due to chemical reactions is of paramount importance for geological subsurface utilisation, since mineral dissolution generally reduces rock stiffness. In the present study, the effective elastic moduli of two digital rock samples, the Fontainebleau and Bentheim sandstones, are numerically determined based on micro-CT images. Reduction in rock stiffness due to the dissolution of 10% calcite cement by volume out of the pore network is quantified for three synthetic spatial calcite distributions (coating, partial filling and random) using representative sub-cubes derived from the digital rock samples. Due to the reduced calcite content, bulk and shear moduli decrease by 34% and 38% in maximum, respectively. Total porosity is clearly the dominant parameter, while spatial calcite distribution has a minor impact, except for a randomly chosen cement distribution within the pore network. Moreover, applying an initial stiffness reduced by 47% for the calcite cement results only in a slightly weaker mechanical behaviour. Using the quantitative approach introduced here substantially improves the accuracy of predictions in elastic rock properties compared to general analytical methods, and further enables quantification of uncertainties related to spatial variations in porosity and mineral distribution.

Calcium carbonate with nanogranular microstructure yields enhanced toughness

The presence of nanogranular microstructures is a widely reported feature of biominerals that form by classical and non-classical mineralization pathways. Inspired by nature, we have synthesized amorphous calcium carbonate nanoparticles with nanogranular microstructures, whose grain size is tuned by varying the polymer concentration. The response to indentation of single calcium carbonate nanoparticles proceeds via an intermittent stick-slip that reflects the characteristics of the nanogranular microstructure. A two-fold mechanism is thus proposed to enhance the toughness of the nanoparticles, namely nanogranular rearrangement and intergranular bridging by an organic phase and/or hydration. This work not only provides a synthesis route to design biologically inspired mineral nanoparticles with nanogranular structure, but also helps in understanding toughening mechanisms of biominerals arising from their nanoscale heterogeneity.

Core and surface microgel mechanics are differentially sensitive to alternative crosslinking concentrations

Microgel mechanics are central to the swelling of stimuli-responsive materials and furthermore have recently emerged as a novel design space for tuning the uptake of nanotherapeutics. Despite this importance, the techniques available to assess mechanics, at the sub-micron scale, remain limited. In this report, all mechanical moduli for a series of air-dried, polystyrene-co-poly(N-isopropylacrylamide) (pS-co-NIPAM) microgels of varying composition in monomer and crosslinker (N,N'-methylene-bisacrylamide (BIS)) mol% have been determined using Brillouin light scattering (BLS) and AFM nanoindentation. These techniques sample the material through distinct means and provide complementary nanomechanical data. An initial demonstration of this combined approach is used to evaluate size-dependent nanomechanics in pS particles of varying diameter. For the pS-co-NIPAM series, our BLS results demonstrate an increase in Young's (E) and shear moduli with increasing NIPAM and/or BIS mol%, while the Poisson's ratio decreased. The same rank order in E was observed from AFM and the two techniques correlate well. However, at low BIS crosslinking, an inverted particle structure persists and small increases in BIS yield a higher increase in E from AFM relative to BLS, consistent with a higher density at the particle surface. At higher BIS incorporation, the microgel reverts to a typical, dense-core structure and further increasing BIS yields changes to core-particle mechanics reflected in BLS. Lastly, at 75 mol% NIPAM, the microgels displayed a broad volume phase transition and increased crosslinking resulted in a minor, yet unexpected, increase in swelling ratio. This complementary approach offers new insight into nanomechanics critical for microgel design and application.

Using simulation to understand the structure and properties of hydrated amorphous calcium carbonate

The protocols used give a range of behaviours comparable to previous experiments and an insight into the structure of ACC.

Formation of nanoparticles and nanostructures--an industrial perspective on CaCO3 , cement, and polymers

Nanotechnology enables the design of materials with outstanding performance. A key element of nanotechnology is the ability to manipulate and control matter on the nanoscale to achieve a certain desired set of specific properties. Here, we discuss recent insight into the formation mechanisms of inorganic nanoparticles during precipitation reactions. We focus on calcium carbonate, and describe the various transient stages potentially occurring on the way from the dissolved constituent ions to finally stable macrocrystals-including solute ion clusters, dense liquid phases, amorphous intermediates, and nanoparticles. The role of polymers in nucleating, templating, stabilizing, and/or preventing these structures is outlined. As a specific example for applied nanotechnology, the properties of cement are shown to be determined by the formation and interlocking of calcium-silicate-hydrate nanoplatelets. The aggregation of these platelets into mesoscale architectures can be controlled with polymers.

In situ investigation of complex BaSO4 fiber generation in the presence of sodium polyacrylate. 2. Crystallization mechanisms

The formation mechanisms of complex BaSO(4) fiber bundles and cones in the presence of polyacrylate sodium salt via a bioinspired approach at ambient temperature in an aqueous environment are reported. These complex organic-inorganic hybrid structures assemble after heterogeneous nucleation of amorphous precursor particle aggregates on polar surfaces, and the crystallization area can be patterned. In contrast to earlier reports, three different mechanisms based on the oriented attachment of nanoparticles were revealed for the formation of typical fibrous superstructures depending on the supersaturation or on the number of precursor particles. (A) High supersaturation (S > 2): large amorphous aggregates stick to a polar surface, form fiber bundles after mesoscopic transformation and oriented attachment, and then form a narrow tip through polymer interaction. (B) Low supersaturation (S = 1.02-2): only a few fibers nucleate heterogeneously from a single nucleation spot, and amorphous particles stick to existing fibers, which results in the formation of a fiber bundle. (C) Vanishing supersaturation (S = 1-1.02): nucleation of a fiber bundle from a single nucleation spot with self-limiting repetitive growth as a result of the limited amount of building material. These growth processes are supported by time-resolved optical microscopy in solution, TEM, SEM, and DLS.

Nanosized amorphous calcium carbonate stabilized by poly(ethylene oxide)-b-poly(acrylic acid) block copolymers

Particles of amorphous calcium carbonate (ACC), formed in situ from calcium chloride by the slow release of carbon dioxide by alkaline hydrolysis of dimethyl carbonate in water, are stabilized against coalescence in the presence of very small amounts of double hydrophilic block copolymers (DHBCs) composed of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) blocks. Under optimized conditions, spherical particles of ACC with diameters less than 100 nm and narrow size distribution are obtained at a concentration of only 3 ppm of PEO-b-PAA as additive. Equivalent triblock or star DHBCs are compared to diblock copolymers. The results are interpreted assuming an interaction of the PAA blocks with the surface of the liquid droplets of the concentrated CaCO3 phase, formed by phase separation from the initially homogeneous reaction mixture. The adsorption layer of the block copolymer protects the liquid precursor of ACC from coalescence and/or coagulation.