Cluster Growth Research Articles

CO2 Aggregation on Monoethanolamine: Observations from Rotational Spectroscopy.

The initial stages of the gas-phase nucleation between CO2 and monoethanolamine were investigated via broadband rotational spectroscopy with the aid of extensive theoretical structure sampling. Sub-nanometer-scale aggregation patterns of monoethanolamine-(CO2 )n , n=1-4, were identified. An interesting competition between the monoethanolamine intramolecular hydrogen bond and the intermolecular interactions between monoethanolamine and CO2 upon cluster growth was discovered, revealing an intriguing CO2 binding priority to the hydroxyl group over the amine group. These findings are in sharp contrast to the general results for aqueous solutions. In the quinary complex, a cap-like CO2 tetramer was observed cooperatively surrounding the monoethanolamine. As the cluster approaches the critical size of new particle formation, the contribution of CO2 self-assembly to the overall stability increases.

CO2Aggregation on Monoethanolamine: Observations from Rotational Spectroscopy

AbstractThe initial stages of the gas‐phase nucleation between CO2and monoethanolamine were investigated via broadband rotational spectroscopy with the aid of extensive theoretical structure sampling. Sub‐nanometer‐scale aggregation patterns of monoethanolamine‐(CO2)n,n=1–4, were identified. An interesting competition between the monoethanolamine intramolecular hydrogen bond and the intermolecular interactions between monoethanolamine and CO2upon cluster growth was discovered, revealing an intriguing CO2binding priority to the hydroxyl group over the amine group. These findings are in sharp contrast to the general results for aqueous solutions. In the quinary complex, a cap‐like CO2tetramer was observed cooperatively surrounding the monoethanolamine. As the cluster approaches the critical size of new particle formation, the contribution of CO2self‐assembly to the overall stability increases.

Theoretical and mechanistic insights into control factor-assisted CO2 mineralization with olivine

We elucidate the CO2 mineralization mechanism with Mg-rich forsterite via theoretical approach including density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Here, the CO2 mineralization follows two steps: the ion dissolution pathway for dissolving Mg ions from the forsterite surface, and the cluster growth pathway, where ion pairs agglomerate into molecular-sized MgCO3 clusters in aqueous solution. Step-by-step reaction mechanism for the dissolution of Mg ion was investigated via DFT calculations, and the formation procedure of solvated magnesite clusters and their structural changes over time were observed through MD simulations. Afterward, the effects of three control factors of pH, temperature, and hetero-metal ions were studied for both pathways. We found that the adjustment of pH contributed to the structural changes of the mineral surface and clustering ion pairs, which in turn affected the kinetics of reaction pathway. Also, high-temperature condition induced positive effects for accelerating both mineralization pathways. Lastly, calcium and ferrous ions showed opposite effects, promoting and hindering the overall processes, respectively. Importantly, our mechanistic study suggests that the pH of the solution changes alternatively between acid and base conditions during each mineralization pathway and pH condition induced by the preceding mineralization pathway facilitates the subsequent one.

Morphological and structural evolutions of tungsten-tungsten oxide powders after a novel vacuum-reduction thermo-chemical treatment

In the current paper, morphological, chemical and structural evolution of WO3 particles under an interesting thermo-chemical treatment was investigated. This proposed treatment is consisting of partial oxidation of initial tungsten particles at 800 °C under air atmosphere, vacuum heat treatment at 1100 °C and hydrogen reduction at 800 °C, subsequently. The morphological and microstructural investigations of the material during different stages carried out by SEM and EDS analysis. The obtained results confirmed the sever size reduction of initial tungsten powders due to the formation of needle-like tungsten oxide particles after vacuum heat treatment. Formation of cauliflower-like tungsten oxide, the phase transformation from yellow tungsten oxide into brown one after vacuum treatment, and growth of tungsten crystal cluster during hydrogen reduction is the main microstructural observation in this study.

Mutual independence of water and n-nonane nucleation at low temperatures.

The interaction of water with different substances in the earth's atmosphere lies at the heart of many processes that influence our climate. However, it is still unclear how different species interact with water on the molecular level and in which ways this interaction contributes to the water vapor phase transition. Here, we report the first measurements of water-nonane binary nucleation in the 50-110K temperature range, along with unary nucleation data of both. The time-dependent cluster size distribution in a uniform post-nozzle flow was measured by time-of-flight mass spectrometry coupled with single-photon ionization. From these data, we extract experimental rates and rate constants for both nucleation and cluster growth. The observed mass spectra of water/nonane clusters are not or only slightly affected by the introduction of the other vapor, and the formation of mixed clusters was not observed during nucleation of the mixed vapor. Additionally, the nucleation rate of either substance is not much affected by the presence (or absence) of the other species, i.e., the nucleation of water and nonane proceeds independently, indicating that hetero-molecular clusters do not play a role during nucleation. Only at the lowest temperature of our experiment (i.e., 51K) do the measurements suggest that interspecies interaction slows water cluster growth. The findings here are in contrast to our earlier work in which we showed that vapor components in other mixtures, e.g., CO2 and toluene/H2O, can interact to promote nucleation and cluster growth in a similar temperature range.

Nucleation and condensation characteristics of carbon dioxide in natural gas: A molecular simulation perspective

The potential of supersonic separators to remove CO2 from natural gas has received extensive attention. However, microscopic understanding of the condensation mechanism of CO2 in natural gas and the applicability of classical nucleation theory (CNT) is unclear. In this study, we investigated the condensation characteristics of CO2 gas by using computational fluid dynamics (CFD) and molecular dynamics (MD) simulations with a CH4-CO2 mixture gas. The nucleation and growth pathways of CO2 are elucidated from the molecular scale. The results show that the Laval nozzle creates low-temperature conditions for CO2 liquefaction, and that reducing the inlet temperature and increasing the inlet pressure will create more favorable conditions for condensation. In the nucleation stage, CO2 gas molecules collide to form clusters, releasing large amounts of latent heat, leading to repeated condensation and evaporation of CO2 gas, and the stability of the clusters depends on the energy interactions with surrounding molecules. With higher initial pressure and lower cooling temperature, the nucleation phase duration is shortened, the nucleation rate increases, and the cluster growth is accelerated. In addition, CNT deviates from the MD simulation results by 3 ∼ 4 orders of magnitude, and reasonable corrections to the CNT will be made subsequently by combining the results of many MD simulations.

Kinetics of Precipitation Processes at Non-Zero Input Fluxes of Segregating Particles

We consider the process of formation and growth of clusters of a new phase in segregation processes in solid or liquid solutions in an open system when segregating particles are added continuously to it with a given rate of input fluxes, Φ. As shown here, the value of the input flux significantly affects the number of supercritical clusters formed, their growth kinetics, and, in particular, the coarsening behavior in the late stages of the process. The detailed specification of the respective dependencies is the aim of the present analysis, which combines numerical computations with an analytical treatment of the obtained results. In particular, a treatment of the coarsening kinetics is developed, allowing a description of the development of the number of clusters and their average sizes in the late stages of the segregation processes in open systems, which goes beyond the scope of the classical Lifshitz, Slezov and Wagner theory. As is also shown, in its basic ingredients, this approach supplies us with a general tool for the theoretical description of Ostwald ripening in open systems, or systems where the boundary conditions, like temperature or pressure, vary with time. Having this method at one's disposal supplies us with the possibility that conditions can be theoretically tested, leading to cluster size distributions that are most appropriate for desired applications.

Water vapor condensation on substrates with nanoscale hydrophilic spots: A molecular dynamics study

Because of preferable nucleation and departure characteristics, hybrid wetting substrates have been widely used to enhance condensation. Nanoscale hydrophilic spots are expected to reduce the adhesive force between the droplet and substrate, thereby promoting droplet departure; however, whether such hydrophilic spots can enhance nucleation and cluster growth remains poorly understood. Using molecular dynamics simulations, this work studies vapor condensation on a hydrophobic background substrate decorated with nanoscale hydrophilic spots. The results show that on the substrate with larger isolated hydrophilic spots, a higher probability of vapor molecules colliding with hydrophilic spots leads to faster nucleation. In the growth stage, the time-evolved size and surface area of the cluster follow N ∼ t3/2 and A ∼ t, respectively. With a fixed size of hydrophilic spots, increasing the hydrophilic spot density is found to enhance nucleation probability and increase the number of formed clusters; however, the competition between nucleation sites also suppresses the growth of individual clusters. Besides, an interesting phenomenon is observed that there is a critical size of hydrophilic spots below which vapor condensation cannot take place on the spots. This phenomenon can be explained by the fact that the hydrophobic atoms surrounding a hydrophilic spot weaken the affinity of the hydrophilic atoms that are located at the boundary of the hydrophilic spot, and thus reduce the interaction between the hydrophilic spot and vapor molecules. This edge effect will become extremely prominent if increasing the nucleation site number with a fixed hydrophilic atoms ratio. As a result, an appropriate nucleation site number should be designed to obtain the best condensation performance.

Collective rotational motion of freely expanding T84 epithelial cell colonies.

Coordinated rotational motion is an intriguing, yet still elusive mode of collective cell migration, which is relevant in pathological and morphogenetic processes. Most of the studies on this topic have been carried out on epithelial cells plated on micropatterned substrates, where cell motion is confined in regions of well-defined shapes coated with extracellular matrix adhesive proteins. The driver of collective rotation in such conditions has not been clearly elucidated, although it has been speculated that spatial confinement can play an essential role in triggering cell rotation. Here, we study the growth of epithelial cell colonies freely expanding (i.e. with no physical constraints) on the surface of cell culture plates and focus on collective cell rotation in such conditions, a case which has received scarce attention in the literature. One of the main findings of our work is that coordinated cell rotation spontaneously occurs in cell clusters in the free growth regime, thus implying that cell confinement is not necessary to elicit collective rotation as previously suggested. The extent of collective rotation was size and shape dependent: a highly coordinated disc-like rotation was found in small cell clusters with a round shape, while collective rotation was suppressed in large irregular cell clusters generated by merging of different clusters in the course of their growth. The angular motion was persistent in the same direction, although clockwise and anticlockwise rotations were equally likely to occur among different cell clusters. Radial cell velocity was quite low as compared to the angular velocity, in agreement with the free expansion regime where cluster growth is essentially governed by cell proliferation. A clear difference in morphology was observed between cells at the periphery and the ones in the core of the clusters, the former being more elongated and spread out as compared to the latter. Overall, our results, to our knowledge, provide the first quantitative and systematic evidence that coordinated cell rotation does not require a spatial confinement and occurs spontaneously in freely expanding epithelial cell colonies, possibly as a mechanism for the system.

Cluster growth in binary N2–Kr supersonic jets: Effect of initial gas temperature and krypton gas concentration

An electron diffraction diagnostics of substrate-free clusters formed in N2–Kr binary jets expanding through a supersonic nozzle into a vacuum was carried out. Gas mixtures contained 0.5, 1, and 6 mol % krypton, the measured average sizes of aggregations in the cluster beam varied from 500 to 30000 molecules per cluster. A change in the nucleation mechanism in the jet from homogeneous to heterogeneous was revealed when the temperature of the gas mixture at the nozzle inlet T0 decreased from 120 to 100 K, which had a profound effect on the sizes, phase composition, and component composition of the clusters. The effect of cluster growth suppression by adding impurity with stronger intermolecular forces was revealed for the first time. It is shown that the effect is caused by the kinetics of gas condensation in a supersonic jet and is manifested at T0 = 120 K when the krypton gas content increases to 6 mol %. It was established that the intensification of cluster growth by inserted krypton nucleation centers at T0 = 100 K occurs through an increase in the fraction of the fcc phase compared to the hcp.

The impact of endoplasmic reticulum morphology on IRE1 protein clustering.

The Unfolded Protein Response (UPR) is a signaling network that responds to an increased load of unfolded proteins within the Endoplasmic Reticulum (ER), referred to as ER stress. ER stress activates the transmembrane signaling protein IRE1, which subsequently forms oligomers and clusters with signaling activity that modifies target gene expression to reestablish ER homeostasis. Experiments have shown that IRE1 clusters can have complex shapes that form along the ER tube structure, including wrapping around an ER tube, and suggest that IRE1 protein clusters tend to be found on narrower ER tubes. However, the influence of ER morphology on the dynamics of these IRE1 clusters remains largely unexplored. We quantitatively modeled the dynamics of IRE1 protein clusters on a tubular surface, using a kinetic Monte Carlo algorithm that treats the IRE1 proteins as particles undergoing stochastic diffusion. We show that cluster shape exhibits a phase transition from approximately round clusters to clusters that wrap around the ER tube as a cluster becomes sufficiently large or on sufficiently narrow tubes. These wrapped clusters, which easily form on narrow tubes, evaporate much slower compared to circular clusters of equal size that form on larger tubes. The threshold concentration between cluster growth and decay is also lower for wrapped clusters compared to circular clusters, exhibiting greater stability of wrapped clusters under varying cellular concentrations of IRE1. This modeled behavior aligns with experimental observations and suggests cluster wrapping around the ER tube is important to understanding IRE1 cluster dynamics and corresponding signaling. UPR malfunction is implicated in the development of many diseases including neurodegeneration and cancer. By furthering understanding of IRE1 protein clustering, we gain insight into how ER morphology controls the IRE1 behavior and impacts UPR signaling

Cell-cell adhesion control in multicellular assemblies under the influence of external fluid flow.

Understanding the dynamics and viscoelastic properties of growing multicellular bacterial assemblies under external fluid flow is important for many applications. What behaviors are possible, and how they can be controlled with the strength and selectivity of cell-cell adhesins is largely unknown. Here we take a synthetic biology approach by controlling the expression of synthetic cell-cell adhesins in bacterial aggregates attached to a surface while subjecting these aggregates to external fluid flows. We experimentally characterize the phase space of possible behaviors of these aggregates based on flow conditions and adhesion strength. We identify a rich set of behaviors including cluster growth, cluster deformation, and intermittent cell shedding. We present a biophysical model explaining the observed behaviors. These results provide fundamental insights for active matter research, and will inform the behavior of clinical biofilms, the evolutionary constraints of multicellular life, and have applications like active biomaterials, among others.

Modeling contractility kit-mediated cytoskeletal network assembly.

The proper function of the cytoskeleton enables mechanoresponsiveness, the ability of cells to sense and respond to mechanical cues. Myosin II, cortexillin I and IQGAP proteins preassemble in the cytoplasm of Dictyostelium cells into contractility kits (CKs). These CKs are thought to play a pivotal role in the regulation and delivery of contractile proteins to sites of mechanical stress. The IQGAPs complementarily regulate the mechanoresponsiveness of cortexillin I-myosin II elements within CKs. Whereas cells that have only IQGAP2 are highly mechanoresponsive, those that have only IQGAP1 are not. Moreover, double mutants lacking both IQGAPs are also mechanoresponsive, suggesting that IQGAP1 serves as an inhibitor of cortexillin I and myosin II, and part of the role of IQGAP2 is to alleviate IQGAP1's inhibition. To investigate the mechanism of CK self-assembly and the possible molecular means for IQGAP regulation, we developed in SpringSaLaD a coarse-grained excluded-volume molecular model in which all protein polymers are represented by nm-sized spheres connected by spring-like links. The model is parameterized using experimentally measured values acquired through fluorescence cross-correlation spectroscopy (FCCS) and fluorescence correlation spectroscopy (FCS), which describe the interaction affinities and diffusion coefficients for individual molecular components. Simulations of the model provided cluster diffusion coefficients, distributions of cluster sizes, cluster component distributions, and IQGAP ratios in the clusters. Simulations of wild-type and null-mutant conditions revealed that the temporal order of assembly of these kits is dominated by myosin II dimer formation and that IQGAP proteins mediate cluster growth. Additionally, our simulations predicted, and FCCS experiments confirmed, the existence of CKs that incorporate both IQGAP1 and IQGAP2. This molecular model serves to describe the formation of CKs and how their assembly enables and regulates mechanoresponsiveness.

Обеспечение становления и роста кластеров: центральные, региональные и местные власти

The various aspects of the present-day policymaking in relation to the cluster development and growth are analyzed. The concepts of approaches employed in Norway and the US are identi􀏐ied, along with policy tools used to support the cluster creation, functioning and development. Speci􀏐ic features of municipal policymaking are addressed and an overview of the approaches to cluster organization is provided. The policy tools are listed as effective solutions in the context of deploying the currently existing set of policy tools in this area. The set of policy tools in the above-mentioned countries has evolved with their key elements and the decisions adopted by the policy— makers in these countries to put in place the policy tools in the relevant area being addressed. The policy approach to the creation and development of clusters as the tools of industrial policy and area economic development has been formulated while emphasizing that the key policy makers are to be those at the regional and municipal level.

Effect of pyrazine in PEDOT:PSS thin films: Structural, optical, optoelectrical, and electrical analysis

The pristine PEDOT:PSS and different weight amounts of pyrazine in PEDOT:PSS thin films were prepared using the doctor-blading technique on a borosilicate glass substrate. The structural, optical, and electrical properties of the effect of pyrazine in PEDOT:PSS thin films were presented for the first time of this admixed solution. More accuracy in the surface of thin films was observed by atomic force microscopy (AFM) which revealed the granular deposits on the film surfaces. Some hill shapes and the distribution of agglomerated grains were also observed on the thin films. The PEDOT:PSS with pyrazine has a preferred orientation to be an orthorhombic crystal structure. The crystallite sizes were reduced from 230.40 nm to 101.81 nm for 30–60 mg pyrazine in the PEDOT:PSS. The energy band gap (Eg) value of pristine PEDOT:PSS is of 3.50 eV with Urbach energy (EU) of 336.10 meV. The alteration Eg values from 3.52 to 3.67 eV was obtained with the estimated EU values in the range of 283.16–324.62 meV depends on various amounts of pyrazine. The linear optical parameters, i.e., the refractive index, optical electronegativity, real/imaginary dielectric constants, extinction coefficient, and optical conductivity were investigated and explained by the changes in the formation, nucleation, growth of clusters, and particle arrangement. As the spectrum increased, the highest χ(1), χ(3), and n2 values were obtained for the 80 mg pyrazine in PEDOT:PSS of 0.110, 2.562 × 10−14 esu, and 6.219 × 10−13 esu, respectively. The electrical conductivity was clearly increased for pyrazine exceeding 40 mg from 1.85 × 102 to 3.84 × 102 S/cm and the figure of merit was in the range of 4.34 × 10−2 to 4.68 × 10−2 Ω−1. Thus, the novelty of this work can show that pyrazine in the range of 40 mg–80 mg is the optimum condition to synthesize non-linear optical (NLO) materials, organic light-emitting diodes (OLEDs), and organic light-emitting transistors (OLETs).

Influence of Cluster Sources on the Growth Mechanisms and Chemical Composition of Bimetallic Nanoparticles

Metal nanoparticles are omnipresent in today’s applied and fundamental research. Both wet-chemical as well as physical procedures for their fabrication are well-established, where the latter is of particular interest as they supply surfactant-free particles. Particle growth has been investigated for several decades, but due to its complexity, involving kinetic and dynamic processes on various length and time scales, often only phenomenological rules of thumb are available. In this study, we report on bimetallic AgAu nanoparticles and demonstrate how the additional degree of freedom of the chemical composition can be used to derive information about how and where the particles grow, depending on two different cluster source types (hollow magnetron vs laser vaporization). The chemical composition is quantified on the single-particle level using electron-induced X-ray spectroscopy (STEM-EDS) and shows significant differences for the two fabrication routes. Based on molecular dynamics and Monte Carlo simulations, we derive that for hollow cylindrical sources both the mean particle size and the chemical composition are determined within the plasma region, where particles not only grow but also evaporate low-boiling silver. The comparably large plasma plays a decisive role here, as opposed to planar magnetron or laser vaporization sources, where no such evaporation is observed. These results shed light into the complex cluster growth and help understanding and optimizing nanoscale fabrication processes.

Suppressing condensation frosting using micropatterned ice walls

Condensation frosting is encountered ubiquitously in our daily life and numerous industrial applications, rooting many detrimental consequences in heat transfer and mechanical stabilities. In latest decades, both active de-frosting and passive anti-frosting methods have been developed. In this work, we adopt the concept of three-dimensional overlapping dry zones by patterning microscopic ice walls on a smooth substrate, engendering a sustainable frost coverage of less than 13 %. Patterned ice walls prevent vapor deposition on the substrate base by absorbing all incoming moisture on upper sidewalls, leaving the substrate base free of contaminates from both frost and condensate. To ensure vapor preferentially depositing on upper sidewalls, a critical ice wall height exists, below which fine ice grains initiate in the adjacent of the substrate base and grow substantially faster, compromising the anti-frosting performance. The proposed surface shows reasonable durability when exposed to varying substrate supercooling, and frost coverage may increase due to covering and fracturing of the out-of-plane growth of feather-like ice clusters at large substrate supercooling. Our findings provide an effective anti-frosting surface design that doesn’t require any chemical or mechanical modifications on the targeted surfaces, showing great advantages compared to conventional icephobic surface designs.

Effects of Iron Addition on the Collision of Polycyclic Aromatic Hydrocarbon Clusters: A Molecular Dynamics Study

In this work, soot particle size distributions in iron-doped premixed ethylene flames are examined using scanning mobility particle sizer measurements. It is found that iron addition promotes the growth in soot particle size, and the enhanced particle coagulation is inferred to be an important reason. To support that, the influence of iron addition on the coagulation of polycyclic aromatic hydrocarbon (PAH) clusters, the analogue of incipient soot particles, is further investigated using molecular dynamics simulations. Based on the results of hundreds of binary head-on collision simulations, the collision between two coronene-Fe-coronene dimers is found to have a significantly higher coagulation efficiency than that between two coronene dimers. However, this enhancement effect weakens as the size of the PAH monomer increases. Although the coagulation efficiency can be increased by iron addition, the collision frequency is almost unaffected, as revealed from the binary off-central collision simulations. Moreover, the simulation results of coronene cluster growth via coagulation show that iron addition promotes coronene cluster growth, leading to larger cluster size, which may explain the larger soot particle size observed in iron-doped flames.

Treated sediment as substrate component of three containerized ornamental species: effects on marketable and qualitative traits

Carried out within the LIFE17ENV/IT/000347-SUBSED project, this research aimed at investigating the effect of a treated sediment (TS) as substrate component on the quality and marketability of three widespread containerized ornamental species: cherry laurel (Prunus laurocerasus) cv. Novìta, calla lily (Zantedeschia aethiopica) and protea (Protea cynaroides) cv. Little Prince. The TS was mixed with soilless substrates as sphagnum peat, coir, and bark in different proportion (0%, 25% and 50%). In cherry laurel, the TS used in 25 - 50% proportions reduced plant height, slightly altering its attractive vibrant foliage. A positive effect of the TS was evidenced on calla lily, where both tested sediment-based mixtures allowed a copious blooming and flower quality raised as the sediment content increased (TS 50% > TS 25% > TS 0%). Post-harvest longevity and colour of flowers were not affected by substrate composition. The effect of sediment-based substrates on protea growth and blooming showed an opposite trend (TS 0% > TS 25% > TS 50%), with plants grown on 50% v/v TS exhibiting a considerable reduction in plant growth and production of flower clusters, with brighter tones turning towards purple. Based on sale values, the TS proved to be a sustainable alternative for the production of potted ornamentals if properly mixed with other organic matrixes, such as peat and coir.

An Atomistic View of Platinum Cluster Growth on Pristine and Defective Graphene Supports.

Density functional theory (DFT) is used to systematically investigate the electronic structure of platinum clusters grown on different graphene substrates. Platinum clusters with 1 to 10 atoms and graphene vacancy defect supports with 0 to 5 missing C atoms are investigated. Calculations show that Pt clusters bind more strongly as the vacancy size increases. For a given defect size, increasing the cluster size leads to more endothermic energy of formation, suggesting a templating effect that limits cluster growth. The opposite trend is observed for defect-free graphene where the formation energy becomes more exothermic with increasing cluster size. Calculations show that oxidation of the defect weakens binding of the Pt cluster, hence it is suggested that oxygen-free graphene supports are critical for successful attachment of Pt to carbon-based substrates. However, once the combined material is formed, oxygen adsorption is more favorable on the cluster than on the support, indicating resistance to oxidative support degradation. Finally, while highly-symmetric defects are found to encourage formation of symmetric Pt clusters, calculations also reveal that cluster stability in this size range mostly depends on the number of and ratio between PtC, PtPt, and PtO bonds; the actual cluster geometry seemssecondary.