Formation Of Aggregate Structures Research Articles

Amphiphilic Block Copolymer Grafted Multiwalled Carbon Nanotube Based Hierarchical Nanohybrids for Effective Epoxy Toughening

Inspired by the impact of nanostructured hybrids in the toughening of the epoxy matrix, the effect of an amphiphilic triblock copolymer, poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (TBCP) grafted multiwalled carbon nanotube (MWCNT) in the epoxy matrix is investigated. The effect of molecular architecture in determining the mechanical properties is elucidated in detail. The self-assembly of surface engineered MWCNT (MWCNT-g-TBCP) synthesized via the “grafting to” approach and the related formation of aggregated structures in the epoxy are analyzed and correlated with the mechanical performance. The synergisitic effect of the components of the hybrid filler and the hierarchical worm-like arrangement of the grafted filler contribute to an overall enhancement in the fracture toughness of about 367% compared to neat epoxy, without compromising the tensile strength. Further, evaluation of rheological and thermal behavior helped in understanding the processing parameters of the epoxy nanocomposites.

Alkyl chain length and headgroup dependent stability and agglomeration properties of surfactant-assisted colloidal selenium nanoparticles

In this study, we have systematically investigated and reported the growth, stability, and aggregation properties of selenium nanoparticles (Se NPs) in the presence of surfactant systems comprising different head groups and alkyl chain lengths. Here, the n-alkyl sulfates (C10-C14) and n-alkyl trimethylammonium bromides (C12-C18) were used as the anionic and cationic surfactants. The obtained results showed that the shortening in the alkyl chain length both in anionic and cationic groups does not affect the Se NPs morphologically, however it leads to a gradual increase in their mean sizes. It was also found that the surfactants having a cationic head group pave the way for forming the bigger NPs compared to the anionic ones. In addition, especially in the cationic group, the NPs were found to be in an increasing aggregation tendency with decreasing number of carbon atoms in the chain length. On the other hand, it was observed that the absorbance tends to decrease with time both in the anionic and cationic systems. The rate of decrease in the absorbance within the time revealed that the elongation in the alkyl chain length gives rise to a more stable nanoparticle solution for both surfactant systems. Furthermore, the results revealed that the surfactants having an anionic head group kept the Se NPs more stable in their solutions as compared to cationic ones. The scanning electron microscopy images corresponding to absorption measurements taken for certain days suggested that the formation of aggregated structures, which increase along with time in the nanoparticle solution, is responsible for the accelerated decrease in the absorbance as the tail length decreases.

Quantifying the relative contribution of driving factors to the transformation of bauxite residue into a plant growth substrate

The vast stock and increasing amount of bauxite residue with high alkalinity, low nutrient and poor structure poses a significant challenge to plant growth. Although additives have been recognized to have obvious effects on the transformation of bauxite residue to a soil-like media for plant growth, a clear understanding of the quantitative contribution of physicochemical properties to plant growth is missing. This study aimed to discuss the portrayed role and contributions of additives mediated alkalinity, nutrient, and aggregates component in the significant factors of aggregate structure formation and corresponding plants seed germination in bauxite residue. The regulation of pH and total alkalinity in bauxite residue depends on inorganic additives, while for ESP and nutrients, nitrohumic acid and vinegar residue are better than inorganic and citric acid. The silt-clay fraction and microaggregate increased from 35.1% and 25.6% to 40.8% and 31.9% within citric acid addition, respectively, while macroaggregate increased from 39.2% to 49.9% within nitrohumic acid application, indicating citric acid may be more involved in the formation of the fundamental building units of organo-mineral associations in bauxite residue, while nitrohumic acid and vinegar residue may play an important role in continuous aggregation of small particles. For aggregates component, calcium in silt-clay fraction had the largest explanatory power in aggregate stability and germination rate (R2 = 65.6%), followed by Al in 0.25–2 mm size fraction (R2 = 11.1%), while organic complex Fe oxides and Mg in microaggregate explained little variance (R2 = 3.89% and R2 = 1.25%), demonstrating Ca, Fe, and Mg contributed greatly to the formation of microaggregate, while Si and Al contributed greatly to the formation of large aggregate. Besides the dominant role of aggregates component, aggregate stability related to mean weight diameter, large macroaggregates, fractal dimension, and silt-clay fraction plays a more critical role in seed germination.

Effect of Tricarboxylic Acids on the Formation of Hydrogels with Melem or Melamine: Morphological, Structural and Rheological Investigations.

Herein, aggregation behaviors of melem or melamine in the presence of three symmetric carboxylic acids (1,3,5-tris(4-carboxyphenyl)benzene (TPCA), 1,3,5-benzene-tri-carboxylic acid (BTA) and 1,3,5-cyclohexane-tri-carboxylic acid (CHTA)) have been performed to check the influence of acid on the formation of aggregated structures which have been investigated by optical microscopy, FESEM, FTIR, XRD and viscoelastic properties have been explored with rheological studies. Interestingly, melem, that has limited solubility in aqueous medium, forms aggregation that leads to the formation of hydrogels with TPCA. More significantly, hydrogel is formed here by matching the size selectivity. Melem forms hydrogel with only large tricarboxylic acid, whereas melamine produces hydrogel with any kind of its counterpart from small to large tricarboxylic acid derivatives. Present investigations and results provide the strategy of design of organic self-assembled materials having two component systems.

The rhizosphere effect of native legume Albizzia julibrissin on coastal saline soil nutrient availability, microbial modulation, and aggregate formation

In the coastal zones, numerous ecological shelterbelt projects were conducted to protect against natural hazards. However, it is still not fully understood whether phytoremediation with native legume Albizzia julibrissin plantation can improve saline soil structural development or microbial community structure. In this study, a field experiment was conducted to investigate the responses of rhizosphere soil salinity, nutrients, bacterial community, and aggregate structure to A. julibrissin plantation in a recently reclaimed area along Zhejiang coast, China. After ~3-year plantation, rhizosphere soil pH and EC reduced to 8.25 and 0.14 dS·m−1, respectively, belonging to non-saline soil. Meanwhile, total organic carbon (TOC), permanganate-oxidizable carbon (POXC), total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), and ammonium nitrogen (NH4+-N) were significantly increased in rhizosphere soil compared with bare land (P < 0.05). Consequently, rhizosphere soil had favorable habitat condition for copiotrophic bacterial taxa (e.g., Chloroflexi, Acidobacteria, and Bacteroidates), as well as high diversity, complex co-occurrence network, and catabolism related with nutrient cycling. The soil particle size of bare land was < 0.053 mm, while microaggregate (0.053–0.25 mm) and macroaggregate (0.25–2 mm) were formed in the rhizosphere and coupled with C accumulation and Fe removal. Soil aggregates were of great importance to soil fertility with more efficient bacterial network and biogeochemical cycles of nutrients. N-fixing Rhizobiales preferred to inhabit large soil particle and might primarily contribute to N accumulation. Generally, A. julibrissin was a suitable pioneer tree for mudflat reclamation projects, which effectively improved saline soil rhizosphere environment by reducing salinity, accumulating C and N, and promoting microbial community succession, as well as aggregate structure formation.

Quinoline yellow (food additive) induced conformational changes in lysozyme: a spectroscopic, docking and simulation studies of dye-protein interactions

Quinoline yellow (QY) is a synthetic yellow dye widely used as a coloring agent for various foodstuffs. In the current study, we have examined the role of QY on the aggregation propensity of hen egg-white lysozyme (HEWL) under physiological conditions. The dye induced conformational changes in HEWL leading to aggregate formation were identified by circular dichroism (CD), turbidity analysis, fluorescence measurement and microscopic (TEM) imaging. Molecular docking and molecular dynamics simulation studies were also employed to strengthen binding and aggregation results. Our results indicate that 25–100 µM of QY induces aggregation in HEWL, while lower QY concentrations (5 and 10 µM) does not have any effect on the aggregation propensity of HEWL. The kinetics of HEWL aggregation demonstrate nucleation independent aggregation of HEWL without lag phase. On the other hand, far UV-CD analysis illustrated the loss of α-helical structure with the increasing concentration of QY. TEM results also support the formation of aggregate structures in HEWL when exposed to QY. Molecular docking and simulation studies revealed that the HEWL-QY complex is stable as compared to individual entities. In silico analysis also illustrated that QY-induced aggregation of HEWL proceeds through the formation of hydrogen bonds, electrostatic (Pi-Anion) and Pi-Sulfur interactions. The above-mentioned results highlight the possible detrimental effect by food additive dyes, particularly in protein misfolding.

Electrochemically Reduced Graphene Oxide – Noble Metal Nanoparticles Nanohybrids for Sensitive Enzyme-Free Detection of Hydrogen Peroxide

Electrochemically reduced graphene oxide (ERGO) is a versatile material for the electrode modification, which enables modification of the physicochemical properties of the surface by the reduction and reoxidation of oxygen groups. The oxygen functional groups and structural defects of ERGO deposited on a layer of metal nanoparticles facilitate the electron transport and enhance the electrocatalytic properties of the nanoparticles. ERGO layers show moderate-intrinsic electrocatalytic properties towards the electrochemical reduction of hydrogen peroxide. In this contribution, we present studies of ERGO layers on the top of the nanoparticle layer composed of gold nanoparticles stabilized with silicotungstate ligands (Au/SiW12), silver nanoparticles stabilized with silicotungstate ligands (Ag/SiW12), and silver nanoparticles stabilized with phosphomolybdate ions (Ag/PMo12). The nanoparticles are prepared by the reduction of the chloroauric acid or silver nitrate by the partially reduced forms of H4SiW12O40 or H3PMo12O40 acid. The films of nanoparticles are conditioned by the repetitive potential cycling at pH = 6 before the deposition of the graphene oxide (GO) layer. The GO layer is reduced by scanning the potential between − 0.4 and − 1.2 V vs. SCE. Combination of ERGO with Au/SiW12 or Ag/SiW12 nanoparticles results in synergistic enhancement of amperometric responses to hydrogen peroxide. The electrocatalytic current values observed for the NPs-ERGO layers are higher than the sum of the current for the pure NPs layers and the ERGO layer deposited on a glassy carbon electrode. The Ag/PMo12 nanoparticles show poor electrocatalytic currents due to possible formation of aggregate structures. Infrared and Raman spectroscopies are applied to investigate the electrocatalytic layers.

Aggregation determines the selectivity of membrane-active anticancer and antimicrobial peptides: The case of killerFLIP

Host defense peptides selectively kill bacterial and cancer cells (including those that are drug-resistant) by perturbing the permeability of their membranes, without being significantly toxic to the host. Coulombic interactions between these cationic and amphipathic peptides and the negatively charged membranes of pathogenic cells contribute to the selective toxicity. However, a positive charge is not sufficient for selectivity, which can be achieved only by a finely tuned balance of electrostatic and hydrophobic driving forces. A common property of amphipathic peptides is the formation of aggregated structures in solution, but the role of this phenomenon in peptide activity and selectivity has received limited attention. Our data on the anticancer peptide killerFLIP demonstrate that aggregation strongly increases peptide selectivity, by reducing the effective peptide hydrophobicity and thus the affinity towards membranes composed of neutral lipids (like the outer layer of healthy eukaryotic cell membranes). Aggregation is therefore a useful tool to modulate the selectivity of membrane active peptides and peptidomimetics.

Ab initio prediction of structuring/mesoscale inhomogeneities in surfactant-free microemulsions and hydrogen-bonding-free microemulsions.

In this paper, we consider the influence of H-bond donor and acceptor functionalities on the formation of mesoscale inhomogeneities in ternary systems. It was found that hydrogen-bonding re-enforces such structures, but is not necessarily a prerequisite for the occurrence of mesoscale, microemulsion-like structuring in ternary surfactant-free microemulsions (SFME) and consequently, hydrogen-bonding-free microemulsions (HBFME) exist. The evaluated ternary systems were investigated by means of dynamic light scattering (DLS) and computer-based calculation methods. Theoretical COSMO-RS based calculations were applied to provide an explanation for different hydrotropic efficiencies, and COSMOplex calculations were used to predict and evaluate the propensity of the molecules to form mesoscale structures in SFME and HBFME. Microemulsion-like fluctuations could be observed in the COSMOplex simulations and correlate fairly well with the appearance of mesoscopic structures observed in SFME and HBFME, although the free energy differences in the formation of aggregate structures in the investigated systems are very small, in the range of 0.05 kcal mol-1.

Solvent dependent fabrication of bifunctional nanoparticles and nanostructured thin films by self assembly of organosilanes

Designing the self-configured framework of nanoporous lattices, to assemble bifunctional nanomaterials on solid substrates, retaining the well-defined nanogeometry is the chief objectives of the present study. Organofunctionalised alkoxysilanes (3-aminopropyltrimethoxysilane (APTMS), 2-(3, 4-epoxycyclohexyl) ethyltrimethoxysilane (EETMS)) containing the functional groups, amino, epoxy, hydroxyl etc., are the potential candidates for the fabrication of nanostructured and monolayered assembly of mono (PdNPs) and bimetallic (Au@PdNPs, Ag@PdNPs) nanomaterials, via sol–gel processing, in aqueous and non-aqueous media with thickness in the range 6–8 nm. The interactions between the silane coupling agents are studied using dynamic light scattering (DLS) technique. The range of hydrodynamic radii (RH) in different solvents is attributed to the multistage directional alignment of colloidal solutions of alkoxysilane functionalized nanomaterials on solid substrates. The difference in the tendency of the formation of aggregate structures is a function of solvent, critical micelle concentration (CMC) of the surfactant. 2-propanol based colloidal dispersions of nanoparticles are exceptionally more homogenously dispersed and have relatively lower z-average values, as the possibility of cluster formation is reduced. The micellar behavior of APTMS and reactivity of EETMS directs the formulation of the stable and catalytically dynamic nanomaterials. The sensitivity of monolayer deposition lies with the water content of the micellar solution, therefore uniform coating is promised by employing nonaqueous solvents (0.66 nm) which tend to slowdown the rate of condensation. Pore diameter and overall architecture are achieved due to less branched structures of the EETMS and APTMS, which are acting as scaffolds for thin film fabrication, and relative rates of evaporation of solvents.

Synergetics of hardening construction systems

The study of hardening high-strength systems indicates the relation between the potential of synergetics and issues related to structure formation of aggregates produced on the basis of rationally selected construction mixes.The paper considers challenges of the general principles of synergetics and sustainable development of open dissipative systems and their use in industry, as well as their understanding as complete self-regulating nonequilibrium systems. The main objective of the study was to demonstrate that the principles of self-regulating systems development can be applied in construction technology.

Effect of pressure with shear stress on gelatinization of starches with different amylose/amylopectin ratios

Effect of pressure with shear stress on the gelatinization of cornstarch with different amylose/amylopectin ratios (waxy 0/100; maze 23/77; G50 50/50; G80 80/20) was systematically investigated using a high-pressure rheometer. Onset and peak temperature of starch gelatinization as well as the peak viscosity were used to discuss the influence of pressure together with shear stress on the gelatinization of starch granules. The results showed that without shear stress, pressure could resist the gelatinization process due to weak swelling of starch granules and lower quantity of amylose released. However, the shear stress can simply counteract the influence of the pressure since its impact is much high on gelatinization. Under certain pressure and shear stress, both onset and peak temperatures of gelatinization were increased with increasing amylose content, which is in correspondence with the results from differential scanning calorimeter measurement, while the overall viscosity was lower when starches with a higher amylose content was used because part of its granular was not fully dissolved during the measurement. SAXS measurements were used to study the gel structure and stability of starch suspensions. It was found that the scattering intensity of starches in the measured range (0.1–1.0 nm−1) is G80 > waxy, indicating the amount of ordered semi-crystalline structures in amylose is higher. Peak values, q = 0.4 nm−1 and q = 0.2 nm−1, detected for waxy starch under different shear rates, indicates that higher shear stress which plays a dominant role compared with pressure, resulted in more degradation in amylopectin, inhibiting the formation of aggregate structure.

A model of cell surface receptor aggregation

In this paper we construct and analyze a model of cell receptor aggregation. Experiments have shown that receptors in an aggregated state have greatly reduced mobility. We model the effects of this reduced mobility with a density dependent diffusion and study the impact of density dependent diffusion on aggregate formation in a one-dimensional domain. Critical values of receptor diffusivity and receptor activation are found and compared with numerical simulations. We find that the role of density dependant diffusion is quite limited in the formation of aggregate structures. In the case of receptor activation, the analytical results agree very well with the numerical calculations. Finally, we consider our model in higher dimensional domains. In this case our analysis is primarily numerical.

Influence of surface modification on structure formation and micromechanical properties of spray-dried silica aggregates

Spray drying processes were utilized for the production of hierarchical materials with defined structures. The structure formation during the spray drying process and the micromechanical properties of the obtained aggregates depend on the particle–particle interactions, the primary particle size and morphology as well as the process parameters of the spray drying process. Hence, the effect of different primary particle systems prepared as stable dispersions with various surface modifications were investigated on the colloidal structure formation and the micromechanical properties of silica particles as model aggregates and compared to theoretical considerations. The obtained results show that the structure formation of aggregates during the spray drying process for stable suspensions is almost independent on the functional groups present at the particle surface. Further, the mechanical properties of these aggregates differ considerably with the content of the bound ligand. This allows the defined adjustment of the aggregate properties, such as the strength and surface properties, as well as the formation of defined hierarchical aggregate structures.

Heterogeneity in (2-butoxyethanol + water) mixtures: Hydrophobicity-induced aggregation or criticality-driven concentration fluctuations?

Micro-heterogeneity in aqueous solutions of 2-butoxyethanol (BE), a system with closed loop miscibility gap, has been explored via absorption and time-resolved fluorescence measurements of a dissolved dipolar solute, coumarin 153 (C153), in the water-rich region at various BE mole fractions (0 ≤ XBE ≤ 0.25) in the temperature range, 278 ≤ T/K ≤ 320. Evidences for both alcohol-induced H-bond strengthening and subsequent structural transition of H-bond network have been observed. Analyses of steady state and time-resolved spectroscopic data for these aqueous mixtures and comparisons with the results for aqueous solutions of ethanol and tertiary butanol indicate that alcohol aggregation in BE/water mixtures is driven by hydrophobic interaction with no or insignificant role for criticality-driven concentration fluctuations preceding phase separation. Excitation energy dependence of fluorescence emission of C153 confirms formation of aggregated structures at very low BE mole fractions. No asymptotic critical power law dependence for relaxation rates of the type, k ∝ (|T - Tc|/Tc)(γ), with γ denoting universal critical constant, has been observed for both solute's rotational relaxation and population relaxation rates in these mixtures upon either approaching to critical concentration or critical temperature. Estimated activation energies for rotational relaxation rate of C153 and solution viscosity have been found to follow each other with no abrupt changes in either of them at any mixture composition. In addition, measured C153 rotation times at various compositions and temperatures reflect near-hydrodynamic viscosity coupling through the dependence,〈τr〉∝ (η/T)(p), with p = 0.8-1.0, suggesting solute's orientational relaxation dynamics being, on an average, temporally homogeneous.

Infrared spectra analysis of O[sbnd]H on aggregate structure formation of oleamide in sulfuric acid solution

Fourier transform infrared spectrum (FT-IR) combined with Gaussian function linear fitting is applied to analyze the aggregation structure in the system of oleamide mixed with sulfuric acid aqueous solution. The possible aggregation structure is proposed according to the shifts of hydroxyl peaks and the changes of their percentage areas. Results show that the interaction modes between sulfuric acid and oleamide vary with the different proportions of two ingredients. When the molar ratio of sulfuric acid to oleamide is low, the major forms of water existing in the system are bulk-like water and the water combining with N+H as N+H⋯OH2. With the increase of the molar ratio of sulfuric acid to oleamide, N+ forms ion-pair complex through attracting sulfate radical. That may be responsible to the scum-like aggregation.

To the formation of aggregate structures of kidney stones

The work considers the aggregation process of calcium oxalate monohydrate crystals (whewellite) during their crystallization from aqueous solutions. The intensive crystal aggregation during the precipitation is evidenced by a decrease in the bulk concentration against an increase in the crystal size. At the initial stages of crystallization fine particles are mainly captured by larger ones in the form of substance deposition on the initiating centers: organic blobs, dead cells, and so on. During the crystallization the effect of the dominant growth of large aggregates increases; the process develops autocatalytically; fine particles disappear more rapidly than large ones, and the crystal size distribution compresses simultaneously with an increase in the average particle size.

Valine-containing silole: synthesis, aggregation-induced chirality, luminescence enhancement, chiral-polarized luminescence and self-assembled structures

The synthesis of valine-containing silole is reported. The introduction of a chiral valine pendant to silole endows the new compound (1 in Scheme 1) with not only circular dichroism (CD) and chiral-polarized luminescence (CPL), but also an aggregation-induced emission (AIE) property. The AIE effect boosts the fluorescence quantum efficiency, ΦF, from 0.33% in pure THF to a maximum of 18.9% when water is added, which is 57 times higher than that in pure THF. In the thin film state, the ΦF value measured by a calibrated integrating sphere can reach 80.3%, which is 243 times higher than that in the solution state. The amphiphilic valine attachments enable the compound to aggregate into complex architectures by a self-assembling process as revealed by AFM images. This compound self-assembles into helical fibers on the evaporation of its THF solution, which corresponds well with its CD and CPL properties. The addition of a poor solvent such as water or hexane to the THF solution also leads to the formation of aggregated structures, which exhibit helical enhancement or inversion in handedness to different extents.

АГРЕГАТНАЯ СТРУКТУРА ТЕХНОЗЕМОВ НИКОПОЛЬСКОГО МАРГАНЦЕВО–РУДНОГО БАСЕЙНА

&lt;p&gt;The profile distribution of industrial soil’s aggregate structure in the experimental polygon of the Nikopol manganese ore basin has been studied. The soil type and layer depth were the most powerful factors of formation of aggregate structure of industrial soils. The distinctive abilities of aggregate structure dynamics for differentiation of industrial soil type according to their profiles have been defined. The variability of indices of fractions between 10 and 0.25 mm was depended on the industrial soil type and to a lesser degree from the profile allocation. Percentage of structural aggregates with a size 3-1 and 1-0,5 mm were typical for certain levels of a profile also is similar in different industrial soils. There was certain specificity of profile allocation of fractions with a size 10-7 and 7-5 mm, distinguishing industrial soil type from each other.&lt;/p&gt; &lt;p&gt;&lt;em&gt;Keywords&lt;/em&gt;&lt;em&gt;: &lt;/em&gt;&lt;em&gt;aggregate structure, industrial soils,&lt;/em&gt;&lt;em&gt; &lt;/em&gt;&lt;em&gt;recultivation&lt;/em&gt;&lt;em&gt;.&lt;/em&gt;&lt;/p&gt;

Relationship among microstructure, linear viscoelastic behavior and mechanical properties of SBS triblock copolymer-compatibilized PP/SAN blend

Morphological, rheological and mechanical properties of the polypropylene (PP) and poly(styrene-co-acrylonitrile) (SAN) blend containing poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer (ranging from 0 to 20 wt%) were studied by scanning electron microscopy (SEM), small amplitude oscillatory shear analysis, and both tensile and impact tests, respectively. SEM observations showed that SBS reduced the diameter of the SAN dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Close examination of SEM micrographs further revealed that the dispersed phase domains were complex aggregates of SAN particles enveloped and joined together with the SBS compatibilizer in the PP matrix. The variation of the dynamic rheological parameters, including dynamic moduli (G′ and G″), complex viscosity ( $$ \eta^{ * } $$ ), loss factor (tan δ), together with Cole–Cole diagrams, with blend composition particularly at low frequency regions were determined to evaluate the interfacial activity of SBS copolymer. A specific viscoelastic phenomenon, i.e., “the second plateau”, appeared at low frequencies for PP/SAN blend containing 20 wt% of SBS and exhibited a certain dependence on the SBS amount and dispersion state in the matrix. This phenomenon was attributed to the formation of aggregate structure between SAN particles and SBS triblock copolymer. Finally, the results of uniaxial tensile and Charpy impact tests conducted on both unnotched and notched specimens indicated that in PP/SAN blend, SBS functions as both compatibilizer and toughening agent.