Growth Of Aggregates Research Articles

Effect of surfactants on the aggregation and stability of TiO2 nanomaterial in environmental aqueous matrices

The high likelihood of the coexistence of surfactants and engineered nano-materials (ENMs) in aqueous environments redoubles the need to study the effects of surfactants on the behavior and transport of nano-materials. In this study, we chose anionic sodium dodecyl sulfate (SDS) and nonionic nonylphenol ethoxylate (NPEO, Tergitol NP-9) to study the effect of surfactants on the behaviors of a typical TiO2 ENM in water environment. An adsorption isotherm and zeta potential study showed that both surfactants could be adsorbed onto the surface of nano-TiO2 but that only SDS can significantly decrease the zeta potential of TiO2. For a better simulation of the dynamic natural water environment, we conducted a 24-h batch experiment to study the aggregation behaviors of nano-TiO2 in the presence of SDS or NP-9 surfactants and recorded the sedimentation of the aggregates in solutions containing the surfactants over a 24h-period. SDS and NP-9 both reduced the growth of the TiO2 aggregates and retarded the aggregate sedimentation at surfactant concentrations ≥0.015% (w:v). The aggregation of TiO2 was far more remarkable in six environmental water matrices from different natural origins than in Milli-Q water, mainly because of the relatively high ionic strength of the former. The introduction of surfactants, however, still retarded the aggregation and sedimentation of TiO2 in the six environmental water matrices. SDS exerted a stronger reductive effect than NP-9. This study reveals that the presence of surfactants may increase the bioavailability and environmental risk of nanomaterial contaminants by retarding the aggregation and promoting the transport of nanomaterials in natural aqueous environments.

Characteristic scale of heterogeneity of seismically active fault and its manifestation in scaling of earthquake source spectra

Previously, similarity of source spectra of Kamchatka earthquakes with respect to the common corner frequency fc1 and the expressed deviations from similarity for the second fc2 and the third fc3 corner frequencies were revealed. The value of fc3 reflects the characteristic size Lis of fault surface; correspondingly, Lis ≈ vrTis, where vr is the rupture speed and Tis ≈ 1/fc3 is characteristic time. The estimates of fc3 are used for normalizing fc1 and fc2. In this way one obtains dimensionless rupture temporal parametres τ1 and τ2 and can further study the dependence τ2 (τ1). The growth of a rupture is considered as a process of aggregation of elementary fault spots of the size Lis. The dimensionless width of the random front of aggregation is on the order of τ2. The relationship τ2 (τ1) approximately follows power law with exponent β. The estimates of β derived from earthquake populations of Kamchatka, USA and Central Asia (β = 0.35–0.6) agree with values expected from the known Eden’s theory of random aggregation growth and from its generalizations.

Surfactant and Gelation Properties of Acetylsalicylate Based Room Temperature Ionic Liquid in Aqueous Media.

An amphiphilic room temperature ionic liquid (RTIL) containing acetylsalicylate anion of type 1-dodecyl-1-methylpiperidinium acetylsalicylate, [C12mpip][AcSa], is synthesized from the precursor [C12mpip][Cl] by an ion exchange process. The sample is characterized, and its surface active and aggregation behavior in water has been studied and explained. The critical aggregation concentrations (CACs) are determined by a variety of methods, namely, electrical conductivity, surface tension, steady state florescence, and isothermal titration calorimetry (ITC) at different temperatures. As compared to its precursor, [C12mpip][AcSa] has low CAC values, indicating enhanced favorable interactions between the [alkylmpip]+ cation···bulky [AcSa]- anion and also hydrogen bonding of both of the ions with water. The free energy of aggregation ΔG0a is always negative, and both enthalpy and entropy of aggregation drive the aggregation process. The micelle-like aggregates are ellipsoidal in shape. The aggregation numbers are determined from translational diffusion coefficients and florescence quenching measurements. Aggregates of [C12mpip][AcSa] are larger than those of its precursor IL with chloride anion. Therefore, it is evident that the close interactions between the ion pairs of [C12mpip]+···[AcSa]- facilitate packing of more molecules in an aggregate. The steady state and oscillatory rheology measurements in aqueous solutions consisting of mixtures of [C12mpip][AcSa] and sodium salicylate (SS), an hydrotope additive, were carried out. The analysis of zero shear viscosity and moduli properties as a function of concentration and temperature reveals that the addition of SS promotes the growth of small ellipsoid aggregates into large worm-like structures with a typical viscoelastic gel behavior. The moduli properties vs temperature profiles are complex and no hysteresis was produced in heating and cooling modes, suggesting the thermoirreversibile and complex nature of the network structures. The release of the acetylsalicylate anion from the gels could be triggered by simple dilution, and the release occurs due to surface erosion and demicellization.

Controllable 5-sulfosalicylic acid assisted solvothermal synthesis of monodispersed superparamagnetic Fe3O4 nanoclusters with tunable size

Monodispersed Fe3O4 nanoclusters were synthesized in a one-pot solvothermal route with 5-sulfosalicylic acid (SSA) as the functional ligand in a mixed-solvent system of diethylene glycol/ethylene glycol (DEG/EG). Nucleation and aggregation growth model was responsible for the formation of secondary structure of the clusters. In the process, the size of the clusters can be effectively controlled by varying the amounts of SSA and the volume ratio of DEG/EG. The nanoclusters exhibited superparamagnetic properties with high saturation magnetization value of about 68.7emug−1 at room temperature. The water-soluble small-molecule SSA grafted on the surface of Fe3O4 nanocrystals rendered the superparamagnetic clusters dispersible in water, which is crucial for potential applications in biomedical fields.

The analysis of the causes of protein precipitate formation in the blanched soymilk

This paper explored the causes of protein precipitate formation in blanched soymilk prepared by blanching soybeans through studying the changes in composition and amount of protein particles during its thermal processing. Compared with the traditional method of preparing soymilk, blanching changed the thermal aggregation behavior of protein particles. Results showed that when blanching was applied to soybeans, β-conglycinin (7S) was denatured in the blanched soybeans, which resulted in the fixation and aggregation of 7S prior to the grinding processing. Therefore, 7S lost its inhibitory ability on the growth of other protein aggregation, explaining the increased insoluble precipitates in the blanched soymilk.

Kinetics of Antibody Aggregation at Neutral pH and Ambient Temperatures Triggered by Temporal Exposure to Acid.

The purification process of an antibody in manufacturing involves temporal exposure of the molecules to low pH followed by neutralization-pH-shift stress-which causes aggregation. It remains unclear how aggregation triggered by pH-shift stress grows at neutral pH and how it depends on the temperature in an ambient range. We used static and dynamic light scattering to monitor the time-dependent evolution of the aggregate size of the pH-shift stressed antibody between 4.0 and 40.0 °C. A power-law relationship between the effective molecular weight and the effective hydrodynamic radius was found, indicating that the aggregates were fractal with a dimension of 1.98. We found that the aggregation kinetics in the lower-temperature range, 4.0-25.0 °C, were well described by the Smoluchowski aggregation equation. The temperature dependence of the effective aggregation rate constant gave 13 ± 1 kcal/mol of endothermic activation energy. Temporal acid exposure creates an enriched population of unfolded protein molecules that are competent of aggregating. Therefore, the energetically unfavorable unfolding step is not required and the aggregation proceeds faster. These findings provide a basis for predicting the growth of aggregates during storage under practical, ambient conditions.

Composite alginate gels for tunable cellular microenvironment mechanics.

The mechanics of the cellular microenvironment can be as critical as biochemistry in directing cell behavior. Many commonly utilized materials derived from extra-cellular-matrix create excellent scaffolds for cell growth, however, evaluating the relative mechanical and biochemical effects independently in 3D environments has been difficult in frequently used biopolymer matrices. Here we present 3D sodium alginate hydrogel microenvironments over a physiological range of stiffness (E = 1.85 to 5.29 kPa), with and without RGD binding sites or collagen fibers. We use confocal microscopy to measure the growth of multi-cellular aggregates (MCAs), of increasing metastatic potential in different elastic moduli of hydrogels, with and without binding factors. We find that the hydrogel stiffness regulates the growth and morphology of these cell clusters; MCAs grow larger and faster in the more rigid environments similar to cancerous breast tissue (E = 4–12 kPa) as compared to healthy tissue (E = 0.4–2 kpa). Adding binding factors from collagen and RGD peptides increases growth rates, and change maximum MCA sizes. These findings demonstrate the utility of these independently tunable mechanical/biochemistry gels, and that mechanical confinement in stiffer microenvironments may increase cell proliferation.

A Review of Research Progress in the Genesis of Colloform Pyrite and Its Environmental Indications

AbstractColloform pyrite is a special form of nano‐micro polycrystalline aggregation growth, for which a suitable term is “aggregates of nano‐micro crystals”. This kind of colloform texture is observed in various geological bodies, such as ancient sedimentary rocks, modern marine and lake sediments, various types of ore deposits, and modern seafloor hydrothermal vents. This paper summarizes the latest developments and research into the definition, formation mechanisms, and environmental indications of colloform pyrite. There appears to be three main formation mechanisms of colloform pyrite: pseudomorphic replacement; biogenic precipitation; and inorganic precipitation. The morphology, particle size, trace element content and preferential growth orientations of colloform pyrite microcrystals can be important indicators for sedimentary environments, hydrothermal activity, and ore‐forming processes. We suggest that the microscopic features of nano‐micro crystals in colloform pyrite and their aggregation growth patterns need further investigation. The relationships between formation mechanisms of colloform pyrite, organic activity and depositional environments require further exploration. To reveal the nature of nano‐micro grain aggregation growth in colloform pyrite and analyse its growth environment and evolutionary history, it is supposed to apply nanoscientific and nanotechnological methods, further integrate consideration of macroscopic geological backgrounds and microscopic mineral growth phenomena, combine high–resolution imaging systems and in situ quantitative microanalysis methods and constitute a mergence of earth science, thermodynamics and kinetics, life science, material science, and chemistry in the study.

Connecting Microphysical Processes in Colorado Winter Storms with Vertical Profiles of Radar Observations

AbstractTo better connect radar observations to microphysical processes, the authors analyze concurrent polarimetric radar observations at vertical incidence and roughly side incidence during the Front Range Orographic Storms (FROST) project. Data from three events show signatures of riming, aggregation, and dendritic growth. Riming and the growth of graupel are suggested by negative differential reflectivity ZDR and vertically pointing Doppler velocity magnitude |VR| > 2.0 m s−1; aggregation is indicated by maxima in the downward-relative gradient of radar reflectivity at horizontal polarization ZH below the −15°C isotherm and positive downward-relative gradients in |VR| when averaged over time. A signature of positive downward-relative gradients in ZH, negative downward-relative gradients in |VR|, and maxima in ZDR is observed near −15°C during all three events. This signature may be indicative of dendritic growth; preexisting, thick platelike crystals fall faster and grow slower than dendrites, allowing for |VR| to shift toward the slower-falling, rapidly growing dendrites. To test this hypothesis, simplified calculations of the ZH and |VR| gradients are performed for a range of terminal fall speeds of dendrites and isometric crystals. The authors prescribe linear profiles of ZH for the dendrites and isometric crystals, with the resulting profiles and gradients of |VR| determined from a range of particle fall speeds. Both the observed ZH and |VR| gradients are reproduced by the calculations for a large range of fall speeds. However, more observational data are needed to fully constrain these calculations and reject or support explanations for this signature.

Real-time monitoring of amyloid growth in a rigid gel matrix

We demonstrate the real-time monitoring of the growth of amyloid-protein aggregates in a semi-rigid gel environment constructed from a 5% w/v gelatin solution. The kinetics of amyloid fibril growth from reduced and carboxy-methylated κ-casein occurring in the gel medium was contrasted against that obtained in a regular solution assay. Aggregation kinetics were recorded using Thioflavin T fluorescence. Transmission electron microscopy was used to confirm the aggregates' existence and morphology. The current demonstration of controlled amyloid growth in a gel environment represents the first step towards development of an experimental model for investigating the role of spatial and medium factors in the kinetics of aggregation-based proteopathies.

Kinetics of asphaltene aggregation phenomena in live oils

The thorough knowledge of the asphaltene aggregation phenomena and pressure/temperature related kinetics is helpful for accurate prediction/control of the asphaltene issues in all facets of petroleum production/processing. However, characterizing the asphaltene aggregation phenomena in live oils at high pressure-high temperature conditions is not well discussed in the available literature. In this work, the asphaltene aggregation phenomena as well as the kinetics of aggregation at different levels of pressure and temperature are investigated in light and heavy live oils using high pressure microscope. The results are presented and discussed in terms of asphaltene onset pressure, aggregates size-growth, particle size distribution, and fractal dimension of the aggregates. For the samples studied, it was discovered that the de-pressurization process at higher temperatures results in higher asphaltene onset pressure. The oil viscosity reduction with temperature rise is the dominant driving force in earlier asphaltene precipitation rather than the solubility effect of oil/asphaltene. The effect of temperature on asphaltene aggregates growth is much more pronounced in light oil than in heavy oil. In light oil, as the temperature of the de-pressurization process increases the kinetics of asphaltene aggregation changes gradually from diffusion limited aggregation to reaction limited aggregation. In heavy oil, the kinetics of aggregation is mainly governed by slow aggregation or reaction limited control of the aggregation. The observed differences in the mechanisms of asphaltene aggregation may be attributed to the stability/nature of the oil rather than the asphaltene content of oil. The findings of this research reveal that accurate prediction/control of the asphaltene related issues seek to kinetics behavior of the asphaltene aggregation at reservoir conditions of pressure and temperature.

INDUCTION OF NEURONAL DIFFERENTIATION, TAU EXPRESSION, AGGREGATION AND PHOSPHORYLATION BY GROWTH FACTOR REMOVAL AND ACIDIC PH CORRELATES WITH AN ENHANCED PROTEIN CLEARANCE AND RECYCLING IN HUMAN HIPPOCAMPAL NEURAL PRECURSOR CELLS (HHIPPNPCS)

INDUCTION OF NEURONAL DIFFERENTIATION, TAU EXPRESSION, AGGREGATION AND PHOSPHORYLATION BY GROWTH FACTOR REMOVAL AND ACIDIC PH CORRELATES WITH AN ENHANCED PROTEIN CLEARANCE AND RECYCLING IN HUMAN HIPPOCAMPAL NEURAL PRECURSOR CELLS (HHIPPNPCS)

Rice-like hollow nano-CaCO3 synthesis

We have shown that Ca(OH)2 solution is a natural stabilizer for CaCO3 particles. We designed a CO2 bubbling crystallization reactor to produce nano-CaCO3 particles in homogenous size distribution without aggregation. In the experimental set-up, the crystallization region was separated from the stabilization region. The produced nanoparticles were removed from the crystallization region into the stabilization region before aggregation or crystal growth. It was shown that rice-like hollow nano-CaCO3 particles in about 250nm in size were produced with almost monodispersed size distribution. The particles started to dissolve through their edges as CO2 bubbles were injected, which opened-up the pores inside the particles. At the late stages of crystallization, the open pores were closed as a result of dissolution-recrystallization of the newly synthesized CaCO3 particles. These particles were stable in Ca(OH)2 solution and no aggregation was detected. The present methodology can be used in drug encapsulation into inorganic CaCO3 particles for cancer treatment with some modifications.

Soil aggregation and root growth of perennial grasses in a constructed clay minesoil

Studying constructed soils (anthropogenic) in mined areas provides an opportunity to expand the existing knowledge about the formation and stabilization of aggregates, due to the magnitude of ecosystem disruption, that creates a “zero time” scenario. The aim of this study was to evaluate the relationship between the aggregation and the root growth of perennial grasses 103 months after the reconstruction of a constructed minesoil, in a coal mining area located in Candiota/Rio Grande do Sul State, Brazil. The evaluated plant species were Hemarthria altissima, Paspalum notatum cv. Pensacola, Cynodon dactylon cv. Tifton, and Urochloa brizantha. The grass roots promoted the recovery of the soil physical condition in the 0.00–0.10m layer, with a decrease in dry bulk density and an increase in soil macroporosity related to the formation of new aggregates. The decrease in root development of all species below 0.10m depth is the result of the restrictive soil physical conditions, with high bulk density and low macroporosity related to aggregates formed originally by compression. The results of root and soil attributes found in this study suggest a different soil-aggregation hierarchy in compacted constructed minesoils, where first a disintegration occurs of large cohesive aggregates formed by compression followed by a re-aggregation process, with sequential re-formation and stabilization of aggregates. The Urochloa brizantha showed a greater root density, volume, length and area, thus presenting a greater potential to recover the physical attributes of the degraded areas, especially those in the compacted layer below 0.10m depth. The recommendation of this and other species in the reclamation of constructed soils after coal mining should take into account the thickness of the topsoil layer because the roots of these species can grow into the overburden layers and thus accelerate the sulfurization process. The recovery of physical attributes of the constructed minesoil, especially below the 0.00–0.10m layer, is a slow process, possibly due to the low accumulation rates of organic carbon in this layer.

DUST COAGULATION IN THE VICINITY OF A GAP-OPENING JUPITER-MASS PLANET

ABSTRACT We analyze the coagulation of dust in and around a gap opened by a Jupiter-mass planet. To this end, we carry out a high-resolution magnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent due to the magnetorotational instability. From the MHD simulation, we obtain values of the gas velocities, densities, and turbulent stresses (a) close to the gap edge, (b) in one of the two gas streams that accrete onto the planet, (c) inside the low-density gap, and (d) outside the gap. The MHD values are then input into a Monte Carlo dust-coagulation algorithm which models grain sticking and compaction. We also introduce a simple implementation for bouncing, for comparison purposes. We consider two dust populations for each region: one whose initial size distribution is monodisperse, with monomer radius equal to 1 μm, and another one whose initial size distribution follows the Mathis–Rumpl–Nordsieck distribution for interstellar dust grains, with an initial range of monomer radii between 0.5 and 10 μm. Without bouncing, our Monte Carlo calculations show steady growth of dust aggregates in all regions, and the mass-weighted (m-w) average porosity of the initially monodisperse population reaches extremely high final values of 98%. The final m-w porosities in all other cases without bouncing range between 30% and 82%. The efficiency of compaction is due to high turbulent relative speeds between dust particles. When bouncing is introduced, growth is slowed down in the planetary wake and inside the gap. Future studies will need to explore the effect of different planet masses and electric charge on grains.

PH-induced aggregation growth of large Au nanoparticles from zwitterionic ligand-modified small Au nanoparticles

This work reports pH-induced oriented attachment growth of large Au nanoparticles (NPs) from zwitterionic ligand-modified 4nm Au NPs. The growth process was examined using UV⿿vis spectroscopy and transmission electron microscopy. Our results show that the sulfonic acid group in the zwitterionic group is protonated at pH<1.4. This leads to the formation of intermolecular hydrogen bond, which in turn mediates the self-assembly of the zwitterionic ligand-modified 4nm Au NPs into small particle assembly. Driven by the reduction of surface free energy, the primary particles in the assembly can further fuse into larger Au NPs, because they are loosely locked and have sufficient freedom to align their crystallographic orientation. These results achieved provide a relatively easy route to study the oriented attachment growth mechanism because it can be initiated at room temperature.

The origin of chloritoid – 3‐mica pseudomorph growth in staurolite–muscovite schist, Bangriposi (Eastern India)

AbstractAt Bangriposi, variable stages in replacement of staurolite by chloritoid – Na–K–Ca mica shimmer aggregates in muscovite schists provides insight into the complex interplay between fluid flow, mass transfer, and dissolution–precipitation during pseudomorph growth. Idioblastic chloritoid growing into mica caps without causing visible deformation, and monomineralic chloritoid veins (up to 300 μm wide) within shimmer aggregates replacing staurolite attest to chloritoid nucleation in fluid‐filled conduits along staurolite grain boundaries and crystallographic planes. The growth of shimmer aggregates initiated along staurolite margins, and advanced inwards into decomposing staurolite along networks of crystallographically controlled fluid‐filled conduits. Coalescence among alteration zones adjacent to channel fills led to dismemberment and the eventual demise of staurolite. Mass balance calculation within a volume‐fixed, silica‐conserved reference frame indicate the shimmer aggregates grew via precipitation from fluids in response to mass transport that led to the addition of H2O, K2O, Na2O and CaO in the reaction zone, and Al2O3 was transported outward from the inward‐retreating margin of decomposing staurolite. This aided precipitation of chloritoid in veins and in the outer collars, and as disseminated grains in the shimmer aggregates at mid‐crustal condition (~520 ± 20 °C, 5.5 ± 2.0 kbar). Computation using one‐dimensional transport equation suggests that staurolite decomposition involved advection dominating over diffusive transport; the permeation of externally derived H2O caused flattening of chemical potential gradients in H2O and aqueous species, for example, and , computed using the Gibbs method. This suggests that staurolite decomposition was promoted by the infiltration of a large volume of H2O that flattened existing chemical potential gradients. In the initial stages of replacement, chloritoid super‐saturation in fluid caused preferential nucleation and growth of chloritoid at staurolite grain boundaries and in crystallographic planes. As reaction progressed, further chloritoid nucleation was halted, but chloritoid continued to grow as the 3‐mica aggregates continued to replace the remaining staurolite in situ, while the chloritoid‐compatible elements were transported in the water‐rich phase facilitating continued growth of the existing chloritoid grains.

Magneto-optical extinction trend inversion in ferrofluids

Effects of pulse magnetic field on the optical transmission properties of thin ferrofluid (FF) layers were experimentally investigated. It was observed that, under an influence of an external uniform magnetic field, pulses applied to the samples surfaces in normal direction decrease the optical transmission with further returning it to its original state, even before the end of the field pulse. The dependencies of the observed effects on the magnetic pulse magnitude and the samples thickness were investigated. The experimental results are explained using FF columnar aggregates growth and lateral coalescence under influence of a magnetic field, leading to a light scattering type Rayleigh-to-Mie transition. Further evolution of this process comes to a geometrical optics scale and respective macroscopic observable opaque FF columnar aggregates emergence. These changes of optical transmission are non-monotonic during the magnetic field pulse duration with minimal value in the case of Mie scattering, which is known as a magneto-optical extinction trend inversion. The residual inversion was detected after the external magnetic field pulse falling edge. Using molecular dynamics simulation, we showed that a homogeneous external magnetic field is enough for the formation of columnar aggregates and their fusion. The results clarify the known Li theory (Li et al., 2004, 2007), implying an inhomogeneous field as a required prerequisite for the magneto-optical extinction trend inversion phenomenon.

Effects of charge density and molecular weight of cationic polyacrylamides on growth and structural characteristics of ground calcium carbonate aggregates

Effects of charge density and molecular weight of cationic polyacrylamides on growth and structural characteristics of ground calcium carbonate aggregates

Morphology-Specific Inhibition of β-Amyloid Aggregates by 17β-Hydroxysteroid Dehydrogenase Type 10.

A major hallmark of Alzheimer's disease (AD) is the formation of toxic aggregates of the β-amyloid peptide (Aβ). Given that Aβ peptides are known to localise within mitochondria and interact with 17β-HSD10, a mitochondrial protein expressed at high levels in AD brains, we investigated the inhibitory potential of 17β-HSD10 against Aβ aggregation under a range of physiological conditions. Fluorescence self-quenching (FSQ) of Aβ(1-42) labelled with HiLyte Fluor 555 was used to evaluate the inhibitory effect under conditions established to grow distinct Aβ morphologies. 17β-HSD10 preferentially inhibits the formation of globular and fibrillar-like structures but has no effect on the growth of amorphous plaque-like aggregates at endosomal pH 6. This work provides insights into the dependence of the Aβ-17β-HSD10 interaction with the morphology of Aβ aggregates and how this impacts enzymatic function.