Large-sized Aggregates Research Articles

Di-Stimuli Responsive Poly(<i>N</i>-Isopropylacrylamide-co-Diethylaminoethylmethacrylate) Copolymer: Synthesis, Characterization and Investigation of Aqueous Dispersion Properties

We report on the synthesis, characterization and aqueous dispersion properties of well-defined double hydrophilic copolymer with pH- and thermo-responsive segments via atom transfer radical polymerization (ATRP). Poly(N-isopropylacrylamide-co-Diethylaminoethylmeth-acrylate), P(NIPAAm-co-DEAEMA), was prepared by ATRP using methyl-4-bromomethyl benzoate initiator. The product was characterized by proton-nuclear magnetic resonance (1H NMR) and attenuated total reflectance infrared (ATR-IR) spectroscopy. The multi-responsive switching between unimer and two types of micellar aggregates were characterized by temperature-dependent dynamic light scattering (DLS). Self-assembles into two types spherical aggregates in 1 mg/mL (0.0315 mM) aqueous solution, depending on solution pH and temperatures were widely investigated. The result shows two types of aggregate with large (280 nm) aggregate and variable sizes of small (17 nm, 25 nm, 45 nm) aggregates depending on temperature ranges from 26 to 40 °C at pH 4.

Influence of mixture composition on the properties of SCC incorporating metakaolin

This paper studies and evaluates the properties of self-consolidating concrete (SCC) containing different percentages of metakaolin (MK) by varying the mixture components and mixture proportions. In total, 32 mixtures with varied percentages of MK and mixture compositions are investigated for the effects on compressive strength, flowability, passing ability and high-range water-reducer admixture (HRWRA) demand. The percentage of MK, coarse-to-fine aggregate (C/F) ratio, coarse aggregate size, binder content and percentage of air entrained in the mixture are varied to study the influence of these variables on the fresh properties of SCC containing MK. SCC mixtures containing silica fume and SCC containing slag are also tested for comparison. The results show that increasing the percentage of MK up to 20% in SCC increases the compressive strength, viscosity, passing ability and HRWRA demand, but decreases the flowability of the mixture. In addition, the flowability of SCC mixtures improves with larger aggregate size, higher binder content and higher percentage of entrained air. The passing ability of SCC mixtures also improves with lower C/F ratio, larger aggregate size, higher binder content and the inclusion of entrained air in the mixture. The results also indicate that increasing the binder content or increasing the percentage of the entrained air has the most significant effect on improving the fresh properties of SCC mixtures.

Di-Stimuli Responsive Poly(<i>N</i>-Isopropylacrylamide-co-Diethylaminoethylmethacrylate) Copolymer: Synthesis, Characterization and Investigation of Aqueous Dispersion Properties

We report on the synthesis, characterization and aqueous dispersion properties of well-defined double hydrophilic copolymer with pH- and thermo-responsive segments via atom transfer radical polymerization (ATRP). Poly(N-isopropylacrylamide-co-Diethylaminoethylmeth-acrylate), P(NIPAAm-co-DEAEMA), was prepared by ATRP using methyl-4-bromomethyl benzoate initiator. The product was characterized by proton-nuclear magnetic resonance (1H NMR) and attenuated total reflectance infrared (ATR-IR) spectroscopy. The multi-responsive switching between unimer and two types of micellar aggregates were characterized by temperature-dependent dynamic light scattering (DLS). Self-assembles into two types spherical aggregates in 1 mg/mL (0.0315 mM) aqueous solution, depending on solution pH and temperatures were widely investigated. The result shows two types of aggregate with large (280 nm) aggregate and variable sizes of small (17 nm, 25 nm, 45 nm) aggregates depending on temperature ranges from 26 to 40 °C at pH 4.

TiO2 nanoparticle aggregations prepared by nitro-functionalized tripodal ligand as promising candidates for dye-sensitized solar cells

Tripodal tetraamine ligands were nominated as complexing agent in preparation of TiO2 nanoparticle via a two-step sol–gel method. The effect of complexing agents was investigated on the particle and aggregation size as well as optical and photovoltaic properties. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron spectroscopy (TEM), scanning electron microscopy (SEM), and UV–vis spectroscopy. The results showed that the symmetry of ligands has a crucial effect on the size of the particles and the aggregations. Three different tripodal ligands were applied as complexing agents. Larger aggregation size with tiny nanoparticles was obtained from the sample prepared with Nitro-funtionalized ligand and led to improved photovoltaic performance due to enhanced photon scattering in the sample.

Bacterial community composition of size-fractioned aggregates within the phycosphere of cyanobacterial blooms in a eutrophic freshwater lake.

Bacterial community composition of different sized aggregates within the Microcystis cyanobacterial phycosphere were determined during summer and fall in Lake Taihu, a eutrophic lake in eastern China. Bloom samples taken in August and September represent healthy bloom biomass, whereas samples from October represent decomposing bloom biomass. To improve our understanding of the complex interior structure in the phycosphere, bloom samples were separated into large (>100 µm), medium (10–100 µm) and small (0.2–10 µm) size aggregates. Species richness and library coverage indicated that pyrosequencing recovered a large bacterial diversity. The community of each size aggregate was highly organized, indicating highly specific conditions within the Microcystis phycosphere. While the communities of medium and small-size aggregates clustered together in August and September samples, large- and medium-size aggregate communities in the October sample were grouped together and distinct from small-size aggregate community. Pronounced changes in the absolute and relative percentages of the dominant genus from the two most important phyla Proteobacteria and Bacteroidetes were observed among the various size aggregates. Bacterial species on large and small-size aggregates likely have the ability to degrade high and low molecular weight compounds, respectively. Thus, there exists a spatial differentiation of bacterial taxa within the phycosphere, possibly operating in sequence and synergy to catalyze the turnover of complex organic matters.

SERS Correlation Spectroscopy of Silver Aggregates in Colloidal Suspension: Quantitative Sizing Down to a Single Nanoparticle

The slow flocculation of silver nanoparticle (NP) aggregates obtained through p-mercaptobenzoic acid (MBA) linker molecules was analyzed by surface-enhanced Raman scattering (SERS) correlation spectroscopy. We demonstrate that our experimental setup, together with the quantitative exploitation of the SERS intensity autocorrelation functions (ACFs) measured from the MBA molecules, enables to determine quantitatively and in situ the size of the SERS active clusters. Moreover, we show that it is possible to characterize the different states of aggregation during cluster formation simply by measuring the size of such silver aggregates. This has been accurately performed for both larger-size aggregates down to very few NPs only. We finally show that our approach is also sensitive to detect and analyze the SERS signal obtained from MBA molecules sitting on nonaggregated NPs. These experiments pave the way to the in situ characterization of functionalized metal NPs as well as the in situ monitoring of NP aggregation, in conjunction with deriving the optical properties of the as-formed clusters.

Interactions of main chain in folding and self assembly of unfolded protein structure: Enquiries with a serine solubilized nonapeptide

Interactions of the protein main chain are probed for their role in folding and self-assembly. The interactions are assessed with serine nonapeptide Ac-(Ser-Ala)4-Ser-NH2 in poly-L and alternating-L,D structure variations. Being a neutral molecule, Serine nonapeptide has been found to display not only folding-unfolding equilibrium, but also association-dissociation equilibrium as a function of solvent and concentration. Thus scrutiny of intra- and inter-molecular interactions have been undertaken in water, methanol, and DMSO solvents. In water, poly-L peptide displays a PPII-helix conformation which unfolds to extended β-conformation with increase of temperature, apparently in a two-state equilibrium. Poly-L peptide at high concentration and on transfer to the low polarity solvent, methanol, displays ordering as a β-hairpin. This implies folding of the peptide by self assembly. Self assembly and ordering possibly as double-stranded β-helix is also evidence for alternating-L,D peptide. Both isomers were observed to be unfolded in high polarity solvent DMSO. Dynamic light scattering suggests that assembly in both isomers may involve large size aggregates. The results have established that folding and self-assembly can be coupled equilibria dependent upon solute structure, concentration, and solvent. The interactions of the protein main chain involved in folding and self assembly of unfolded structure are illuminated and have been discussed.

Modelling the impact of two different flocculants on the performance of a thickener feedwell

The performance of a thickener feedwell depends not only on its ability to generate large-sized aggregates from feed particles but also on aggregate density. The performance of the flocculant BASF Rheomax® DR 1050 has been previously compared to a conventional anionic flocculant in turbulent pipe flocculation of mineral suspension, suggesting that the flocculant can generate denser aggregates (i.e. larger effective fractal dimension). Such aggregates are generally stronger and reduce the need for solids dilution, with both factors favouring faster settling velocity at the feedwell exit. To investigate the impact of the internal aggregate structure on the flocculation performance of a feedwell, Computational Fluid Dynamics (CFD) simulations of a basic open feedwell with shelf design were carried out for both flocculants. A calcite with a fine particle size (Omyacarb 5) was modelled to emphasise the impact of the flocculation process on flow fields at the feedwell exit. Simulations were conducted using CFX-4.4 two-phase flow formulation incorporating equations for a population balance model of the flocculation process. The impact of the fractal dimension on the effectiveness of the aggregation process is presented for low and high solids concentrations. Comparison of the performance of the flocculants is presented in terms of both predicted mean aggregate size and settling flux.

Hydrogels Facilitated by Monovalent Cations and Their Use as Efficient Dye Adsorbents

Gelation behavior of lithocholate (LC(-)) mixed with different monovalent cations in water was detected. The hydrogels consisting of tubular networks were formed by introducing alkali metal ions and NH4(+) to lithocholate aqueous solutions at room temperature. The formation of tubular structures was considered to be mainly driven by the electrostatic interaction with the assistance of a delicate balance of multiple noncovalent interactions. It is interesting that the increase in temperature can induce a significant enhancement in strength of the hydrogels, accompanied by the formation of bundles of tubules and larger size aggregates. The mechanism of the temperature-induced transition can be explained by the "salting-out" effect and the electric double layer model. The hydrogels showed very high adsorption efficiency and adsorption capability for the cationic dyes and were promising to act as toxic substance adsorbents.

Sonication-induced formation of size-controlled self-assemblies of amphiphilic Janus-type polymers as optical tumor-imaging agents.

In this study, amphiphilic Janus-type polymers were synthesized via ring-opening metathesis polymerization (ROMP), multiple vicinal diol formation, and grafting of poly(ethylene glycol) monomethyl ether (mPEG). These amphiphilic polymers formed self-assemblies, which were a mixture of micelles and multimicellar aggregates, in water. By choosing suitable Janus-type polymers and irradiating an aqueous solution of polymers using a sonicator, either small micelles or large multimicellar aggregates were obtained selectively. Hydrophobic substituents controlled the aggregation-disaggregation behavior, leading to the formation of metastable self-assemblies by sonication. The formation of self-assemblies with a uniform size was affected by ultrasonic frequency, rather than power. In vivo optical tumor imaging revealed that the large-size multimicellar aggregates persisting for a long time in blood circulation slowly accumulated in tumor tissues. In contrast, the tumor site was rapidly, clearly visualized using the small-size micelles.

Effects of simulated puddling intensity and pre-drying on shrinkage capacity of a paddy soil under long-term fertilization

Soil structure in paddy fields is affected by different practices such as long-term fertilization and temporal puddling and drying. However, their interactive effects remain unclear. The objectives of this study were to determine the effects of long-term fertilization on soil structural stability at different puddling intensities and to determine the effects of puddling intensity and pre-drying on shrinkage behavior upon drying. Soil samples were taken from long-term experiments established in 1981 and puddling intensity was simulated by mixing soil in water at different speeds using an electronic mixer. Compared with no fertilization and chemical fertilization treatments, the organic amendment treatments had higher soil organic carbon concentration, and larger aggregate stability under the low and moderate puddling intensities. The shrinkage capacity (COLE) of the puddled soils ranging from 0.124 to 0.229 was larger in the organic amendment treatments than in other treatments without pre-drying. The difference in COLE among the treatments diminished with increasing puddling intensity and after the pre-drying. The shrinkage curves and their fitted parameters demonstrated that the larger shrinkage capacity in the organic amendment treatments resulted from the increases in the macro- and meso-pores due to the presence of more large size aggregates after puddling. The macro-pores were lost after the intensive puddling and the meso-pores collapsed after the pre-drying at the proportional shrinkage stage, resulting in no differences in the shrinkage curve among the field treatments. These results suggest that continuous organic amendment may be needed to maintain a porous structure of paddy soil through the increase in resistance to puddling and its influence on the shrinkage capacity upon drying.

Phosphorus recovery from wastewater by struvite crystallization: Property of aggregates

Struvite crystallization is a promising method to remove and recover phosphorus from wastewater to ease both the scarcity of phosphorus rock resources and water eutrophication worldwide. To date, although various kinds of reactor systems have been developed, supporting methods are required to control the struvite fines flushing out of the reactors. As an intrinsic property, aggregation is normally disregarded in the struvite crystallization process, although it is the key factor in final particle size and therefore guarantees phosphorus recovery efficiency. The present study developed a method to analyze the characteristics of struvite aggregates using fractal geometry, and the influence of operational parameters on struvite aggregation was evaluated. Due to its typical orthorhombic molecular structure, struvite particles are prone to crystallize into needle or rod shapes, and aggregate at the corners or edges of crystals. The determined fractal dimension (Dpf) of struvite aggregates was 1.52–1.31, with the corresponding range of equivalent diameter (d0.5) at 295.9–85.4 μm. Aggregates formed in relatively low phosphorus concentrations (3.0–5.0 mmol/L) and mildly alkaline conditions (pH 9.0–9.5) displayed relatively compact structures, large aggregate sizes and high aggregation strength. Increasing pH values led to continuous decrease of aggregate sizes, while the variation of Dpf was insignificant. As to the aggregate evolution, fast growth in a short time followed by a long steady stage was observed.

The self-assembly properties of a series of polymerizable cationic gemini surfactants: Effect of the acryloxyl group

A new series of polymerizable cationic gemini surfactants bearing acryloxyl group in spacer and a variable alkyl chain length were synthesized and their surface active properties alongside with their self-assembly properties were investigated by surface tension measurement, electrical conductivity, fluorescence and dynamic light scattering (DLS) measurements. As compared to single-chain surfmer, this study shows that the gemini surfmers possess low critical micellar concentration (cmc) value and the surface tension value at cmc (γcmc). While compared to corresponding gemini surfactant without acryloxyl group, the introduction of the acryloxyl group into spacer results in a lower cmc value, higher degree of ionization and micropolarity of aggregate. The aggregates with large hydrodynamicradius (Rh) of 70–110nm as the main component were observed in the surfmer solution, while the size of aggregate constructed by corresponding gemini surfactant without acryloxyl group is far smaller than the former. All the results can be attributed to the existence of intramolecular dipolar interaction between the carbonyl of acryloxyl group and the cationic nitrogen atom. This increases the hydrophobicity and the regularity of the molecule, which induces the formation of tighter and larger size aggregate in comparison with corresponding gemini without the acryloxyl group on the spacer.

Relationship between Asphalt Composition and Thermal Behaviour for Solar Energy Collection

Using asphalt to harvest solar energy is an ideal and sustainable solution to the problems involved with increasing energy demand and using fossil fuels. Asphalt has the most heat absorbent colour and is already covering large surfaces in and between urban areas. Asphalt solar collection systems have not been implemented on a large scale worldwide. This is because the current energy/heat collection efficiency does not outweigh the costs involved in constructing on road level and under/within adjacent buildings which can use the energy. This paper is based on testing and evaluation of variations in asphalt composition which can provide a greater quantity of energy/heat in a given time, to increase effectiveness of energy collection to make this system more feasible. Also there is a discussion of other research on asphalt thermal properties, characteristics and factors other than asphalt involved in energy collection. The potential application of this research is also discussed in this paper. The results showed that an increase of 1% in bitumen can increase the maximum temperature of asphalt by almost 14%. In addition, decreasing void ratio, using other aggregates and larger aggregate sizes can increase the maximum temperature and thermal conductivity.

Inhibition of Antithrombin and Bovine Serum Albumin Native State Aggregation by Heparin

Protein native state aggregation, a major problem in pharmaceutical and biological processes, has been addressed pharmacologically by the addition of protein-binding excipients. Heparin (Hp), a highly sulfated polysaccharide, interacts with numerous proteins with moderate to high affinity, but reports about its effect on protein aggregation are contradictory. We studied the pH dependence of the aggregation of antithrombin (AT) and bovine serum albumin (BSA) in the presence and absence of heparin. High-precision turbidimetry showed strong aggregation for both AT and BSA in I = 10 mM NaCl, conditions at which electrostatically driven Hp binding and aggregation both occur, with more obvious aggregation of heparin-free AT appearing as larger aggregate size. Aggregation of AT was dramatically inhibited at Hp: protein 6:1 (mole ratio); however, the effect at 0.5:1 Hp:protein was greater for BSA. Frontal analysis capillary electrophoresis showed a much larger equilibrium association constant Kobs between Hp and AT, in accord with the onset of Hp binding at a higher pH; both effects are explained by the higher charge density of the positive domain for AT as revealed by modeling with DelPhi. The corresponding modeling images showed that these domains persist at high salt only for AT, consistent with the 160-fold drop in Kobs at 100 mM salt for BSA-Hp binding. The smaller inhibition effect for AT arises from the tendency of its uncomplexed monomer to form larger aggregates more rapidly, but the stronger binding of Hp to AT does not facilitate Hp-induced aggregate dissolution which occurs more readily for BSA. This can be attributed to the higher density of AT aggregates evidenced by higher fractal dimensions. Differences between inhibition and reversal by Hp arise because the former may depend on the stage at which Hp enters the aggregation process and the latter on aggregate size and morphology.

Aggregation and soil organic carbon fractions under different land uses on the tableland of the Loess Plateau of China

Land uses and cultivation are important factors controlling SOC storage on the Loess Plateau. These factors may also affect the relative importance of different mechanisms for the stabilization of organic matter in the soil. Easily oxidizable organic carbon (EOC), aggregation and aggregate C fractions in the soil were measured under different land uses. Aggregates were fractionated using a wet-sieving procedure to obtain the distribution of water-stable aggregates. The fractions of aggregates, aggregate SOC and aggregate EOC in grassland and forestland were generally higher than those in farmland. Furthermore, because conventional cultivation destroyed aggregates, the dominant aggregate size fractions were <0.5mm for farmland and >0.5mm for other land uses. Compared to the corresponding values in farmland, the mean weight diameter (MWD) in forestland and grassland increased by 808%–417%, and the stability ratio of water-stable aggregate (WSAR) increased by 920%–553%. Aggregate formation and its dominant size fraction were associated closely with its carbon fractions. SOC and EOC in farmland tended to be concentrated in smaller-sized aggregates, whereas SOC and EOC under other land uses tended to concentrate in larger-sized aggregates. EOC tended to concentrate in larger aggregates than SOC. The small fractions of the aggregates formed large fractions by combining with fresh organic matter. So converting slope farmland to forestland and grassland could improve the storage and quality of SOC, and the tendency of SOC transfer.

Concentration-dependent antagonistic persuasion of SDS and naphthalene derivatives on the fibrillation of stem bromelain

Sodium dodecyl sulfate, a biological membrane mimetic, can be used to study the conversion of globular proteins into amyloid fibrils in vitro. Using multiple approaches, the effect of SDS was examined on stem bromelain (SB), a widely recognized therapeutic protein. SB is known to exist as a partially folded intermediate at pH 2.0, situation also encountered in the gastrointestinal tract (its site of absorption). In the presence of sub-micellar SDS concentration (500–1000μM), this intermediate was found to exhibit great propensity to form large-sized β-sheeted aggregates with fibrillar morphology, the hall marks of amyloid structure. We also observed inhibition of fibrillation by two naphthalene-based compounds, ANS and bis-ANS. While bis-ANS significantly inhibited fibril formation at 50μM, ANS did so at relatively higher concentration (400μM). Alcohols, but not salts, were found to weaken the inhibitory action of these compounds suggesting the possible involvement of hydrophobic interactions in their binding to protein. Besides, isothermal titration calorimetry and molecular docking studies suggested that inhibition of fibrillation by these naphthalene derivatives is mediated not just through hydrophobic forces, but also by disruption of π–π interactions between the aromatic residues together with the inter-polypeptide chain repulsion among negatively charged ANS/bis-ANS bound SB.

Protein cohesion induced by metal ions observed with fluorescence correlation spectroscopy

Nine metal ions were evaluated in the point of denaturating action of proteins. When some metal ions were added to the diluted protein solutions, aggregates appear: stronger denaturation causes the appearance of the larger-size aggregate. The size of the aggregatates are determined by fluorescence correlation spectroscopy (FCS). Green fluorescent protein (ZsGreen) and PE(phycoerythrin)-conjugated human-antibody monoclonal protein were employed as the target protein, of which solution was diluted 100–500 times and mixed with metal ions. According to this process, the denaturation power of metal ions is in the order of Mn2+≈ Fe2+< Co2+< Ni2+< Tl+< Cd2+< Cu+< Cu2+< Pb2+for ZsGreen, and Tl+≈ Ni2+< Cd2+< Fe2+< Cr3+≪ Pb2+for PE-conjugated antibody protein. Pb2+exhibits the strongest power of denaturation. In the case of ZsGreen, the denaturation power of metal ions is on the order of the Irving-Williams series, which provide the coordination tendency against ligands possessing nitrogen and oxygen. The present method with FCS is effective to evaluate the denaturation power of metal ions against proteins.

Seasonal assessment of experimental vertical-flow constructed wetlands treating domestic wastewater

The aim of this work was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand (COD) loading) variables on the long-term and seasonal performance of vertical-flow constructed wetland filters operated in tidal flow mode. Compliance was achieved regarding ammonia-nitrogen, nitrate-nitrogen and suspended solids (SS), and non-compliance concerning biochemical oxygen demand (BOD) and ortho-phosphate-phosphorus. The filter with the highest COD loading performed the best regarding outflow COD concentration. Higher COD inflow concentrations had a significantly positive impact on the treatment performance for COD, ortho-phosphate-phosphorus and SS. The wetland with the largest aggregate size had the lowest mean nitrate-nitrogen outflow concentration. However, the results were similar regardless of aggregate size and resting time for most variables. Clear seasonal outflow concentration trends (low in summer) were recorded for COD, ammonia-nitrogen and nitrate-nitrogen. No filter clogging was observed.

Study on Strength Mechanism of Self-Compacting Rock-Fill Concrete with Big Aggregates

Self-compacting rock-fill concrete with natural and recycled aggregate can be applied in large structural components’production. According to the deep analysis of material's mechanical properties test data, the author makes a study on the strength mechanism of the concrete material. The results show that the concrete material essentially is concrete, and the concrete strength of large-sized natural aggregate and recycled aggregate are basically the same. However, due to the varieties in material production process and material shape as well as the influence of the mechanical properties and aggregate size, the strength mechanism of them is different. Effective control on mechanical properties of self-compacting rock-fill concrete and aggregate's appearances and shapes is helpful to the strength design of the self-compacting rock-fill concrete with large aggregate.