Growth Mechanism Research Articles

A morpho-viscoelasticity theory for growth in proliferating aggregates.

Despite significant research efforts in the continuum modeling of biological growth, certain aspects have been overlooked. For instance, numerous investigations have examined the influence of morphogenetic cell behaviors, like division and intercalation, on the mechanical response of passive (non-growing) tissues. Yet, their impact on active growth dynamics remains inadequately explored. A key reason for this inadequacy stems from challenges in the continuum treatment of cell-level processes. While some coarse-grained models have been proposed to address these shortcomings, a focus on cell division and cell expansion has been missing, rendering them unusable when it comes to modeling growth. Moreover, existing studies are limited to two-dimensional tissues and are yet to be formally extended to three-dimensional multicellular systems. To address these limitations, we here present a generalized multiscale model for three-dimensional aggregates that accounts for complex morphogenetic movements that include division, expansion, and intercalation. The proposed continuum theory thus allows for a comprehensive exploration into the growth and dissipation mechanics of proliferating aggregates, such as spheroids and organoids.

Electrodeposition of Au Nanowires via Amine Ligand-Induced Active Surface Growth.

Amine ligands have been widely applied as morphology-directing reagents in nanostructure synthesis. In this work, we explored the application of the amine ligands in the active surface growth mechanism in place of the strong thiolated ligands. Despite being weaker compared to the thiols, amine ligands such as aniline were also shown to be capable of facilitating the template-less electrodeposition of Au nanowires (NWs) on the substrate via the active surface growth mechanism. Given the close binding difference between the amine-grafted substrate and the ligands, substrate functionalization becomes critically important for effective construction of the active surface and the growth of the nanowires. Additionally, the growth with the amine ligands took place at more positive reduction potentials and is less prone to splitting and bundle formation. A systematic generality study revealed that besides the aromatic amines, long-chain aliphatic amines were also capable of facilitating nanowire growth. Given the weak binding affinity of the amine ligands, the Au NWs are readily accessible for further processing to generate sophisticated one-dimensional structures. As a demonstration, tandem electrodeposition was performed to directly obtain coaxial core-shell Au@Pt NWs with adjustable length, diameter, and shell thickness.

Curvature-Induced Electron Spin Catalysis with Carbon Spheres.

Here, we report curvature-induced electron spin catalysis by using solid carbon spheres as catalysts, which were synthesized using positive curvature molecular hexabromocyclopentadiene as a precursor molecule, following a radical coupling mechanism. The curvature spin of carbon is regarded as an overlapping state of σ- and π-radical, which is identified by the inverse Laplace transform of pulse-electron paramagnetic resonance. The growth mechanism of carbon spheres abiding by Kroto's model, is supported by the density functional theory study of thermodynamics and kinetics calculations. The solid carbon spheres present excellent catalytic behaviour of oxidation coupling of amines to form corresponding imines with the conversion of >99%, selectivity of 98.7%, and yield of 97.7%, which is attributed to the predominantly curvature-induced electron spin catalysis of carbon, supported by the calculation of oxygen adsorption energy. This work proposes a view of curvature-induced spin catalysis of carbon, which opens up a research direction for curvature-induced electron spin catalysis.

Curvature‐Induced Electron Spin Catalysis with Carbon Spheres

Here, we report curvature‐induced electron spin catalysis by using solid carbon spheres as catalysts, which were synthesized using positive curvature molecular hexabromocyclopentadiene as a precursor molecule, following a radical coupling mechanism. The curvature spin of carbon is regarded as an overlapping state of σ‐ and π‐radical, which is identified by the inverse Laplace transform of pulse‐electron paramagnetic resonance. The growth mechanism of carbon spheres abiding by Kroto’s model, is supported by the density functional theory study of thermodynamics and kinetics calculations. The solid carbon spheres present excellent catalytic behaviour of oxidation coupling of amines to form corresponding imines with the conversion of >99%, selectivity of 98.7%, and yield of 97.7%, which is attributed to the predominantly curvature‐induced electron spin catalysis of carbon, supported by the calculation of oxygen adsorption energy. This work proposes a view of curvature‐induced spin catalysis of carbon, which opens up a research direction for curvature‐induced electron spin catalysis.

Deposition temperature-mediated growth of helically shaped polymers and chevron-type graphene nanoribbons from a fluorinated precursor.

Graphene nanoribbons (GNRs) of precise size and shape, critical for controlling electronic properties and future device applications, can be realized via precision synthesis on surfaces using rationally designed molecular precursors. Fluorine-bearing precursors have the potential to form GNRs on nonmetallic substrates suitable for device fabrication. Here, we investigate the deposition temperature-mediated growth of a new fluorine-bearing precursor, 6,11-diiodo-1,4-bis(2-fluorophenyl)-2,3-diphenyltriphenylene (C42H24F2I2), into helically shaped polymer intermediates and chevron-type GNRs on Au(111) by combining scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory simulations. The fluorinated precursors do not adsorb on the Au(111) surface at lower temperatures, necessitating an optimum substrate temperature to achieve maximum polymer and GNR lengths. We compare the adsorption behavior with that of pristine chevron precursors and discuss the effects of C-H and C-F bonds. The results elucidate the growth mechanism of GNRs with fluorine-bearing precursors and establish a foundation for future synthesis of GNRs on nonmetallic substrates.

Enhanced mud retention as an autogenic mechanism for sustained delta growth: Insight from records of the Lafourche subdelta of the Mississippi River

ABSTRACTMud deposition is acknowledged as a significant contributor to delta architecture, yet its role is often oversimplified as a constant parameter in models of delta formation. A better understanding of mud retention on deltas would resolve remaining questions regarding delta growth. This study explores how spatiotemporally varied mud retention facilitates sustained delta growth in defiance of the concept of autoretreat, that is, the idea that shoreline progradation rates decline as a delta grows due to the expansion of subaqueous and subaerial delta surfaces. This research is inspired by prior field observations of the river‐dominated Mississippi Delta, USA, where the shoreline of a ca 6000 to 8000 km2 subdelta prograded at a constant rate for roughly a millennium, despite its expanding delta surface, compaction and sea‐level rise. For this, a laterally averaged one‐dimensional numerical model is leveraged to test hypotheses that enhanced mud retention with time in: (i) the delta bottomset; and (ii) the delta plain (floodplain) supports a constant rate of shoreline progradation in a maturing delta. Results demonstrate that enhanced mud retention in both the bottomset and delta plain facilitates sustained delta growth. Neither component by itself can replicate the case study. Yet, with these two integrated components, the model reproduces the cross‐section and linearly prograding pattern observed in the Mississippi Delta. The findings provide an autogenic mechanism for sustained delta growth and support the importance of mud as a fundamental building block of deltas that should be incorporated in delta‐growth models of engineered river diversions.

Spiral-concave Prussian Blue Crystals with Rich Steps: Growth Mechanism and Coordination Regulation.

Investigating the formation and transformation mechanisms of spiral-concave crystals holds significant potential for advancing innovative material design and comprehension. We examined the kinetics-controlled nucleation and growth mechanisms of Prussian Blue crystals with spiral concave structures, and constructed a detailed crystal growth phase diagram. The spiral-concave hexacyanoferrate (SC-HCF) crystals, characterized by high-density surface steps and a low stress-strain architecture, exhibit enhanced activity due to their facile interaction with reactants. Notably, the coordination environment of SC-HCF can be precisely modulated by the introduction of diverse metals. Utilizing X-ray absorption fine structure spectroscopy and in-situ ultraviolet-visible spectroscopy, we elucidated the formation mechanism of SC-HCF to Co-HCF facilitated by oriented adsorption-ion exchange (OA-IE) process. Both experimental data, and density functional theory confirm that Co-HCF possesses an optimized energy band structure, capable of adjusting the local electronic environment and enhancing the performance of the oxygen evolution reaction. This work not only elucidates the formation mechanism and coordination regulation for rich steps HCF, but also offers a novel perspective for constructing nanocrystals with intricate spiral-concave structures.

Spiral‐concave Prussian Blue Crystals with Rich Steps: Growth Mechanism and Coordination Regulation

Spiral‐concave Prussian Blue Crystals with Rich Steps: Growth Mechanism and Coordination Regulation

Fabrication of double modified electrocatalyst by dual flame synthesis for enhancing electrochemical reduction of carbon dioxide

A rapid dual flame synthesis is developed for one-step preparation and modification of double modified ZnO catalysts with carbon doping and oxygen vacancies. The growth mechanism and nanostructure evolution are also investigated. The double modified ZnO with carbon doping and oxygen vacancies exhibies excellent performance in CO2 reduction to syngas, with a high current density of 14.02 mA/cm2 at −1.1 V vs. RHE and a maximum Faradaic efficiency of 71% for CO production. The maximum adjustable range of the CO/H2 ratio from 0.5 to 2.7. In a flow cell, the double modified ZnO exhibits a large current density of 126.8 mA/cm2 at −1.2 V vs. RHE. The maximum Faradaic efficiency for CO2 reduction to CO is 74.8% at 50 mA/cm2. Double modified ZnO maintains stable potential and Faradaic efficiency for over 5 h of electrolysis. Operando X-ray absorption spectroscopy and density functional theory calculations reveal that the active site is the Zn–Zn configuration, and that carbon dopant and oxygen vacancy promote CO2 activation and CO desorption, and reduce reaction overpotential of CO2RR.

A dual growth mode unique for organic crystals relies on mesoscopic liquid precursors.

Organic solvents host the synthesis of high-value crystals used as pharmaceuticals and optical devices, among other applications. A knowledge gap persists on how replacing the hydrogen bonds and polar attraction that dominate aqueous environments with the weaker van der Waals forces affects the growth mechanism, including its defining feature, whether crystals grow classically or nonclassically. Here we demonstrate a rare dual growth mode of etioporphyrin I crystals, enabled by liquid precursors that associate with crystal surfaces to generate stacks of layers, which then grow laterally by incorporating solute molecules. Our findings reveal the precursors as mesoscopic solute-rich clusters, a unique phase favored by weak bonds such as those between organic solutes. The lateral spreading of the precursor-initiated stacks of layers crucially relies on abundant solute supply directly from the solution, bypassing diffusion along the crystal surface; the direct incorporation pathway may, again, be unique to organic solvents. Clusters that evolve to amorphous particles do not seamlessly integrate into crystal lattices. Crystals growing fast and mostly nonclassically at high supersaturations are not excessively strained. Our findings demonstrate that the weak interactions typical of organic systems promote nonclassical growth modes by supporting liquid precursors and enabling the spreading of multilayer stacks.

A method to obtain the trapping energy and trapping range between hydrogen and defects at finite temperature

The binding energy between hydrogen (H) and defects in solid phase materials has been widely studied, which is of vital importance to understand the H retention effects and defect growth mechanisms. However, present studies of binding energy through density functional theory (DFT) or the molecular statics (MS) method were usually performed at 0 K, which could not take the influence of entropy into consideration. In this work, a thermodynamic method has been proposed to obtain the trapping energy between H and defects at finite temperatures. The method is based on the rate theory, which uses trapping energy (V) and trapping range (δ) to describe the trapping properties of defects. Ultimately, a parameterized H spatial cumulative distribution function at thermodynamic equilibrium state could be given. The trapping energy and trapping range parameters in the function can be determined by contrast with the results obtained from molecular dynamics or other methods. This method has been applied to calculate the trapping energies and trapping ranges of H to helium bubble and grain boundary, respectively. Further discussion has been made on the discrepancy between trapping energies obtained by this method and the conventional DFT/MS method.

Development of the full Lagrangian approach for modeling dilute dispersed media flows (a review)

Continuum models of media with zero pressure are widely used in various branches of physics and mechanics, including studies of a dilute dispersed phase in multiphase flows. In zero-pressure media, the particle trajectories may intersect, “folds” and “puckers” of the phase volume may arise, and “caustics” (the envelopes of particle trajectories) may appear, near which the density of the medium sharply increases. In recent decades, the phenomena of clustering and aerodynamic focusing of inertial admixture in gas and liquid flows have attracted increasing attention of researchers. This is due to the importance of taking into account the inhomogeneities in the impurity concentration when describing the transport of aerosol pollutants in the environment, the mechanisms of droplet growth in rain clouds, scattering of radiation by dispersed inclusions, initiation of detonation in two-phase mixtures, as well as when solving problems of two-phase aerodynamics, interpretation of measurements obtained by LDV or PIV methods, and in many other applications. These problems gave an impetus to a significant increase in the number of publications devoted to the processes of accumulation and clustering of inertial particles in gas and liquid flows. Within the framework of classical two-fluid models and standard Eulerian approaches assuming single-valuedness of continuum parameters of the media, it turns out impossible to describe zones of multi-valued velocity fields and density singularities in flows with crossing particle trajectories. One of the alternatives is the full Lagrangian approach proposed by the author earlier. In recent years, this approach has been further developed in combination with averaged Eulerian and Lagrangian (vortex-blob method) methods for describing the dynamics of the carrier phase. Such combined approaches made it possible to study the structure of local zones of accumulation of inertial particles in vortex, transient, and turbulent flows. This article describes the basic ideas of the full Lagrangian approach, provides examples of the most significant results which illustrate the unique capabilities of the method, and gives an overview of the main directions of further development of the method as applied to transient, vortex, and turbulent flows of “gas-particle” media. Some of the ideas discussed and the results presented below are of a more general interest, since they are also applicable to other models of zero-pressure media.

Growth mechanisms of amorphous nanoparticles in solution and during heat drying

The purpose of this study was twofold: to identify the growth mechanisms of amorphous nanoparticles in solution and during the drying process at high temperatures, and to guide the process condition and stabilizer selection for amorphous nanoparticle formulations. In contrast to nanocrystals that are mostly mechanically robust, amorphous nanoparticles tend to undergo deformation under stress. As a result, development of a stable formulation and evaluation of the drying process for re-dispersible amorphous nanoparticles presents considerable challenges. Although amorphous nanoparticles have stability issues, they have several pros in terms of production, high monodispersity, and diverse applications in drug delivery. In this study, amorphous nanoparticles were prepared via liquid-liquid phase separation, and their growth mechanisms were investigated both in solution and during the drying process. In solution, particles were found to be susceptible to flocculation, crystallization, coalescence, and Ostwald ripening, with coalescence being a preliminary step providing the driving force for Ostwald ripening. However, during the heat drying process, coalescence and crystallization were found to be the primary mechanisms for particle growth, with Ostwald ripening being negligible due to reduced molecular mobility. The glass transition temperature (Tg) of these amorphous nanoparticles was found to be a crucial factor both in solution and during the drying process. At temperatures < Tg, particles remained in a rigid, glassy state thereby inhibiting coalescence, whereas at or above Tg, particles transition from glassy to rubbery state, making them more susceptible to deformation and coalescence. The mechanistic understanding of particle growth from this study can also be extended to the stabilization of other types of soft nanoparticles.

Dual-Porous ZIF-8 Heterogeneous Catalysts with Increased Reaction Sites for Efficient PET Glycolysis

Poly(ethylene terephthalate) (PET) has been widely used for drink bottles, food packing, films, and fibers, resulting in millions of tons of waste PET. Less than 10% of that waste is recycled, and the rest is discarded or incinerated. Waste PET upcycling employs chemical recycling and particularly glycolysis to create the bis(2-hydroxyethyl) terephthalate (BHET) monomer. Herein, we report a dual-porous zeolitic imidazolate framework-8 nanoparticle (DPZIF-8) heterogeneous catalyst for efficient PET glycolysis. The DPZIF-8 nanoparticles were prepared using a triethylamine modulator, which can control the nucleation and growth mechanisms of the ZIF-8 nanoparticles. The DPZIF-8 nanoparticles include both intrinsic micropores and particle-particle adhesion-induced mesopores that can provide a larger external surface area of the zinc sites in the ZIF-8 architecture. The PET glycolysis catalyzed by DPZIF-8 at 180 °C and 1 atm for 4 h shows a PET conversion of 91.7% and a BHET yield of 76.1%, the latter particularly being much higher than with a traditional heterogeneous ZIF-8 catalyst. This dual-porous structure rational design strategy can be versatile for other metal–organic frameworks (MOFs) to increase the interfacial catalytic reaction sites between the metal–organic framework and the polymer, enhancing the PET depolymerization performance and efficiency.

In situ growth of ultrathin covalent triazine frameworks on unmodified cellulose II beads for enhanced dye pollutant removal

cellulose II beads@covalent triazine frameworks (CBCs) are prepared by in situ growth of ultra-dispersed covalent triazine frameworks (CTF) using unmodified regenerated cellulose beads (CBs) as templates. The CBCs as a whole are three-dimensional structures consisting of a layered pore structure and a continuous ultrathin CTF, which combines a functional surface with highly efficient mass transfer. The thickness of the CTF in the prepared CBCs can be controlled at 32–83 nm, which enables the CBC to have a dye adsorption efficiency of up to 191 mg g−1 and an ultrafast dye removal time (Methylene Blue, 0.5 min, 95 %). Molecular dynamics simulations revealed the mechanism for CTF growth on the surface of unmodified cellulose II rather than on the surface of cellulose Ⅰ, and the effects of the hydrophilic/hydrophobic surfaces of cellulose I and cellulose II on the growth of CTF were determined. This is the first use of unmodified cellulose II as a template for the in situ growth of ultrathin CTF and provides important insights into dynamic CTF-cellulose interactions. This research provides a new cost-effective strategy for preparation of ultra-dispersed CTF based on large-scale cellulose templates.

Near-bulk resistivity of sub-10nm Au films by breaking free from thickness downscaling effects

The miniaturization of electronic devices requires thin films with electrical conductivities that are comparable to those of bulk metals. However, ultrathin coinage metal films inevitably suffer from increased electrical resistivity compared with bulk metals, hindering their performance in miniaturized electronics. This study presents a novel approach to achieve near-bulk resistivity in sub-10-nm-thick Au films on heterogeneous oxide substrates. Our method utilizes O-incorporated epitaxial growth of Au films on α-Al2O3(0001) substrates followed by thermal treatment. This strategy promoted an exceptional film crystallinity, particularly favoring the Au(111) orientation, and significantly reduced the resistivity. Notably, the 8-nm-thick Au film exhibited a record-low resistivity of 3.7 μΩ⋅cm, approaching that of a significantly thicker (60-nm) Au film. This performance surpasses those of Cu and Ag film electrodes of similar thicknesses. Density functional theory calculations provided theoretical insights into the mechanism of O-induced epitaxial growth. Our findings demonstrate that improved crystallinity mitigates the strong dependence of resistivity on the thickness reduction. This study challenges the conventional view of resistivity increase in ultrathin metal films and offers a promising path toward high-performance miniaturized electronics with superior electrical properties.

SO3 removal by submicron absorbents synthesized via inhibition method: The product layer grows like parallel peaks

Injecting calcium hydroxide powder into the flue gas is an effective strategy for SO3 removal. However, commercial calcium hydroxide has several disadvantages, including large particle size, low efficiency, and unsuitability for excessive grinding. In this work, sub-micron calcium hydroxide was synthesized by an inhibition method and its performance for SO3 removal from flue gas was investigated on a pilot-scale platform (120 Nm3/h). When the concentration of sodium alginate solution was 100 mg/L, the average particle size of calcium hydroxide decreased from 13.66 µm to 0.84 µm, which improved the SO3 removal (92.1 %) and conversion of the absorbent. The results of the fixed-bed experiments indicate that the absorption kinetics of the reaction is consistent with the Bangham model. In addition, density functional theory verifies that calcium hydroxide captures SO3 by chemisorption. The AFM image shows that the calcium sulfate whiskers produced during the reaction grow like parallel peaks on the adsorbent surface. The calculations suggest that the driving force for SO3 adsorption originates from Ca-p orbital (Ca(OH)2) and O-s orbital (SO3) hybridization. This study complements the island growth mechanism for gas-solid two-phase reactions and provides an effective method for removing SO3 from flue gas in coal-fired power plants. In addition, it will provide an important reference for the development of submicron adsorbents.

Investigation of simultaneous production of H2 and separable carbon from CH4 in a fluidised bed of NiO/Ca2Fe2O5/CaO particles

This work investigated the possibility of simultaneous production of hydrogen/syngas and separable solid carbon in a fluidised bed by using CH4-CO2 cycles and exploring the carbon growth over solid catalytic particles of NiO/Ca2Fe2O5/CaO. This two-stage process included i) stage I: H2-rich gas and carbon were simultaneously generated from the interaction between CH4 and NiO/Ca2Fe2O5/CaO particles; and ii) stage II: the reduced/carbon-deposited particles were regenerated in CO2. Following our previous successful demonstration of the process for stable hydrogen production over cycles, this study focused on the formation of solid carbon and aimed at understanding its growth mechanism as well as demonstrating the potential of using fluidisation as a means of automatic carbon separation. By tracking the carbon growth history and the change in phases of the reacted NiO/Ca2Fe2O5/CaO particles at temperatures from 700 to 900 °C, we discovered the formation of various forms of nano-structured carbon from CH4 conversion (e.g. partial oxidation, pyrolysis). These include carbon nanotubes (CNTs), carbon graphite sheets, carbon onions (CNOs), and carbon fibres. Amorphous carbon was also observed, particularly in the initial stage of CH4 conversion. Higher temperatures like 800 °C and 900 °C gave faster kinetics of CH4 conversion and more formation of solid carbon. Fe3C phase was observed on the reduced catalytic particles and could act as an intermediate phase or carbon sink for carbon growth. The results suggested that other mechanisms for carbon deposition, such as directly over Fe sites, may also exist. Fluidisation with a higher U/Umf ratio separated more carbon-rich fines from the bulk catalytic particles in the fluidised bed. Fluidising with air at 700 °C effectively removed amorphous carbon on the reacted catalytic particles, whilst structured carbon remained. Full separation and purification to obtain pure carbon require furthers optimisation of e.g. fluidisation parameters and material design.

Modelling and verification of the nickel electroforming process of a mechanical vane fit for Industry 4.0

In previous studies, the comprehensive scaling-up of nickel electroforming on a lab-scale rotating disk electrode (RDE) suggested that secondary current distribution could adequately simulate such a forming process. In this work, the use of a 3-D, time-dependent, secondary current distribution model, developed in COMSOL Multiphysics®, was examined to validate the nickel electroforming of an industrial mechanical vane, a low-tolerance part with a demanding thickness profile of great interest to the aerospace industry. A set of experiments were carried out in an industrial pilot tank with computations showing that the model can satisfactorily predict the experimental findings. In addition, these experiments revealed that the local applied current density was related to the surface appearance (shiny vs matt) of the electroform.Simulations of the process at applied current densities ≤5A/dm2 satisfactorily predicted the experimentally observed thickness distribution while, simulations of the process at applied current densities ≥5A/dm2 underpredicted the experimentally achieved thicknesses. Nevertheless, it is proposed that the model can be used for either quantitative or qualitative studies, respectively, depending on the required operating current density on a case-by-case basis. Scanning electron microscopy was used to determine the microstructure of the electroforms and determine the purity of nickel (i.e., if nickel oxide is formed), with imaging suggesting that pyramid-shaped nickel particles evolve during deposition. Another interesting observation revealed a periodicity in the deposit's growth mechanism which leads to “necklace”-like deposit layers at the areas where the electroforms presented the highest thickness.

Study on the dendritic growth and grain boundary formation in the suddenly expanded cross-section of single crystal superalloy during directional solidification process

The dendritic growth behavior at the suddenly expanded cross-section of single crystal blades dramatically affects the defects formation. In this work, the dendrite growth mechanism is deeply investigated in the rectangular platform by analyzing the quasi-three-dimensional microstructures via the continuous image shooting and orientation scanning, combined with simulating the thermal fields at different furnace temperatures. As the solidification proceeds to the platform, the secondary branches at the connection between the primary zone and the expansion zone grow outwardly. Some secondary branches growth direction deflects the preferred orientation. The well-developed tertiary arms would develop on some secondary branches. The different generation dendrites with the different growth directions converge and form the boundary angles. The tertiary proportion and the dendrite boundary lengthes/angles show the decrease tendency as the temperature increases. The undercooling in the platform edges and corners from the concave/convex degree of isothermal surface should be responsible for the formation and convergence of the different generation dendrites the matrix dendrite expanding behavior towards the platform edge and their subsequent upward directional growth. The nonuniformity of thermal gradient at the isothermal surface should affects the inconsistency of the growth directions of the different dendrites, which provides the more opportunity for the dendrite deviation. This study sheds light on the dendrite growth behavior when the single crystal blade directionally solidifies through the suddenly expanded platform.