Aggregation Phenomena Research Articles

Silver Nanoparticles Grown on Cross-Linked Poly (Methacrylic Acid) Microspheres: Synthesis, Characterization, and Antifungal Activity Evaluation

Silver nanoparticles (AgNPs) exert profound physicochemical, biological, and antimicrobial properties, therefore, they have been extensively studied for a variety of applications such as food packaging and cultural heritage protection. However, restrictions in their stability, aggregation phenomena, and toxicity limit their extensive use. Hence, the use of functional substrates that promote the silver nanoparticles’ growth and allow the formation of uniform-sized, evenly distributed, as well as stable nanoparticles, has been suggested. This study reports on the fabrication and the characterization of hydrophilic polymer spheres including nanoparticles with intrinsic antifungal properties. Poly (methacrylic acid) microspheres were synthesized, employing the distillation precipitation method, to provide monodisperse spherical substrates for the growth of silver nanoparticles, utilizing the co-precipitation of silver nitrate in aqueous media. The growth and the aggregation potential of the silver nanoparticles were studied, whereas the antifungal activity of the produced nanostructures was evaluated against the black mold-causing fungus Aspergillus niger. The produced structures exhibit dose-dependent antifungal activity. Therefore, they could potentially be employed for the protection and preservation of cultural heritage artifacts and considered as new agents for food protection from fungal contamination during storage.

The Assembly of the Mixture of Two Ionic Surfactants in Polyols Media at Variable Temperatures: Combined Conductivity and Theoretical Investigations

AbstractHerein, the aggregation phenomena of the two cationic amphiphiles, the hexadecyltrimethylammonium bromide (CTAB), and tetradecyltrimethylammonium bromide (TTAB), has been investigated in the presence of monosaccharide (glucose) and disaccharide (maltose) at varying compositions and temperatures. The critical micelle concentration (cmc), degree of ionization (g), and several thermodynamic properties have been estimated applying the conductivity measurement technique. To explore the consequence of additives on the mixed micellization of TTAB + CTAB, glucose as monosaccharide having two concentrations (1% & 5% (w/w) glucose) and maltose as disaccharide containing single concentration (1% (w/w)) have been employed. Together with the mixture of TTAB and CTAB, investigation of the physicochemical parameters of pure amphiphiles in glucose and maltose solutions was quantified. The efficiency of the additives in depressing the cmc values followed the order: 1 (w/w) % maltose >5 (w/w) % glucose >1% (w/w) glucose. The ideal cmc (cmcid), activity coefficients, and β values suggested the synergistic attraction (attractive force) between these two surfactants. By utilizing the Rubingh model, the evaluated micellar mole fractions of CTAB (α1) coupled with the ideal mole fraction () imply the increase of the contribution of CTAB in the mixed micellization with rising the α1 values. The values of the negative excess free energy () implied the stability of the mixed micelle formed. The changes in standard enthalpy (ΔH°m) and changes in standard entropy (ΔS°m) of micellization reveal the presence of different modes of interactions like electrostatic, ion‐dipole, H‐bonding, and hydrophobic interactions among the studied components.

Polymer-mediated drug supersaturation – A spotlight on the interplay between phase-separated amorphous drug colloids and dissolved molecules

HypothesisColloidal aggregation phenomena have been found responsible for the supersaturation of poorly water-soluble drugs, potentially leading to bioavailability enhancements. Unlike coarse precipitates, phase separation in the form of colloids, is expected to enhance drug supersaturation performance. Therefore, a high proportion of these colloids should correlate with the extent and the kinetics of supersaturation. The prime objective of the current study is to provide a mechanistic understanding on supersaturation for the model drug albendazole (ALB) in combination with twelve polymers. ExperimentsSpecies separated after a pH-shift were characterized by dynamic light scattering (DLS), freeze-fracture electron microscopy (FF-EM) and transmission X-ray diffraction (XRD). Laser diffraction (LD) in a liquid cell was introduced for a relative quantification of the colloidally separated species, described as colloid fraction. The pH-dependent supersaturation was assessed online using a miniaturized dissolution assay. FindingsHere, a measure of the extent of amorphous colloidal phase separation was established, and its impact on supersaturation was evaluated. As a result, a correlation was found between the extent of supersaturation and the colloid fraction. This confirmed the dependence of polymer-mediated enabling and preservation of supersaturation on the ability of polymers to stabilize colloid fractions. Furthermore, a fixed ratio was suggested between the dissolved drug and colloidally separated drug as the kinetic profiles of both species showed similar trajectories. In conclusion, colloid fractions were identified to be responsible for dissolved and potentially bioavailable drug molecules.

The laser-induced damage mechanism of amorphous and crystalline Sc2O3 films

This paper investigated the laser-induced damage mechanism of amorphous and crystalline scandium oxide (Sc2O3) films prepared by ion beam sputtering (IBS) and annealed at different temperatures. A significant increased laser-induced damage threshold (LIDT) at 355 nm wavelength was obtained by amorphous film annealed slightly below the crystallization temperature, which was above 300% higher than those of crystalline films. Meanwhile, the damage morphologies of amorphous and crystalline films were totally different. Measurement of the absorption of films showed that higher absorption led to a large distinction between the LIDTs of films. Energy dispersive spectroscopy (EDS) patterns revealed very uniform distributions of elements without obvious aggregation phenomenon. Positron annihilation spectroscopy (PAS) indicated that vacancy defect increased the absorption and heavily reduced the resistance of films for 355 nm wavelength laser. The investigation in this study would promote the understanding of the laser-induced damage mechanism of amorphous and crystalline films and provide an effective method to increase LIDTs at 355 nm wavelength.

Monte Carlo Risk Assessment of Formation Damage Caused by Asphaltene Deposition

Summary Uncertainties regarding the factors that influence asphaltene deposition in porous media (e.g., those resulting from oil composition, rock properties, and rock/fluid interaction) strongly affect the prediction of important variables, such as oil production. Besides, some aspects of these predictions are stochastic processes, such as the aggregation phenomenon of asphaltene precipitates. For this reason, a well-defined output from an asphaltene-deposition model might not be feasible. Instead of this, obtaining the probability distribution of important outputs (e.g., permeability reduction and oil production) should be the objective of rigorous modeling of this phenomenon. This probability distribution would support the design of a risk-based policy for the prevention and mitigation of asphaltene deposition. In this paper we aim to present a new approach to assessing the risk of formation damage caused by asphaltene deposition using Monte Carlo simulations. Using this approach, the probability-distribution function of the permeability reduction was obtained. To connect this information to a parameter more related to economic concepts, the probability distribution of the damage ratio (DR) was also calculated, which is the fraction of production loss caused by formation damage. A hypothetical scenario involving a decision in the asphaltene-prevention policy is presented as an application of the method. A novel approach to model the prevention of asphaltene aggregation using inhibitors has been proposed and successfully applied in this scenario.

Interdisciplinarity, Ethics and Territorial Planning

Representing a phenomenon of social aggregation, the settlements of the rock civilization of Fasano and Monopoli in Brindisi, Italy and their recovery, is one of the objectives pursued by the technical-scientific committee of the San Domenico Foundation, which involves experts at national and international level. This paper, presented at the 8th International Conference, intends to highlight how art, as a testimony of these settlements in the area of this rock civilization, is not attributable only to beauty, but also to ethics, and as such, is synonymous with identity. This leads to concepts and meanings deriving from interdisciplinarity, sustainability, planning, territorial development, as well as the need to train a specialized and multi-faceted professional figure who is qualified to operate in the field of the protection and valorisation of the past, in order to be able to competently pass it on through to the future

Lubrication Performance Distribution of Large Aspect Ratio Water-Lubricated Bearings Considering Deformation and Shaft Bending

In order to solve the problem that the assumption of the straight shaft is inconsistent with the actual situation of marine water-lubricated journal bearings, the journal bending curve was identified by calculating the three-dimensional mechanical model of propulsion shafting.- A fluid–solid coupling model of water-lubricated journal bearings considering journal bending was proposed. The results show that the simulation values matched the experiment values well at partial sections by a full-circumference film pressure distribution experiment with the full-size bearing. The journal bending line caused the water film pressure to peak at both ends of the bearing and caused the lubrication performance distribution to gather to one side. As eccentricity increases and Young’s modulus of lining decreases, the aggregation phenomenon is aggravated, maximum film pressure and carrying capacity increase, and minimum film thickness and friction coefficient decrease.

Ionizable Drug Self-Associations and the Solubility Dependence on pH: Detection of Aggregates in Saturated Solutions Using Mass Spectrometry (ESI-Q-TOF-MS/MS).

It is widely accepted that solubility-pH profiles of ionizable compounds follow the Henderson-Hasselbalch equation. However, several studies point out that compounds often undergo additional processes in saturated solutions, such as sub-micellar oligomerization, micellar aggregation, or drug-buffer complexation among others, which make the experimental profiles deviate from the behavior predicted by the Henderson-Hasselbalch equation. Often, the presence of additional processes is supported by the analysis of experimental data through solubility computer programs. However, the purpose of this work is to experimentally prove the aggregation phenomena for a series of bases for which deviations from the theoretical profile have been observed. To this end, five monoprotic bases (lidocaine, maprotiline, cyproheptadine, bupivacaine, and mifepristone) susceptible to form ionic aggregates in solution have been selected, and mass spectrometry has been the technique of choice to prove the presence of aggregation. High declustering potentials have been applied to prevent aggregates from forming in the ionization source of the mass spectrometer. In addition, haloperidol has been used as a negative control since according to its profile, it is not suspected to form ionic aggregates. In all instances, except for haloperidol, the analysis of the saturated solutions revealed the presence of mixed-charged dimers (aggregates formed by a neutral molecule and a charged one) and even trimers in the case of mifepristone and bupivacaine. For lidocaine, the most soluble of the compounds, the presence of neutral aggregates was also detected. These experiments support the hypothesis that the simple Henderson-Hasselbalch equation may explain the solubility-pH behavior of certain compounds, but it can be somewhat inaccurate in describing the behavior of many other substances.

Influences of alcohol and diol on the aggregation behaviour, modes of interaction and the thermodynamic properties of the mixture of bromocresol green dye and sodium dodecyl sulphate at numerous temperatures

The aggregation of the mixture of anionic surfactant – sodium dodecyl sulfate (SDS), and an anionic dye – bromocresol green sodium salt (BCG) was investigated by conductometric technique in water and alcoholic/diolic media within a temperature range of 300.55–320.55 K (with 5 K interval). The observed critical micelle concentration (cmc) decreases with surging of the concentration of BCG, following the same trend for β value. In presence of additives (ethanol, propanol, and ethylene glycol), the cmc value decreases up to a certain concentration and then the cmc values start enhancing with increasing concentration in all the cases. With the increased additive percentage, the β values continually decrease. Again, the cmc value increases gradually with the increase of temperature both in water and aq. additives media. The free energy of studied aggregation phenomena is negative which experiences an augmentation with the escalation of temperature. The increased negative value of free energy at elevated temperature indicates that the process becomes more spontaneous at a higher temperature. The and values reveal that the probable interaction forces between BCG and SDS are hydrophobic, ion-ion, as well as electrostatic interactions.

High structural stability and hydrogen storage properties of nano-porous Zr-Al-Ni-Pd glassy alloy produced by electrochemical dealloying

Nano-porous glassy Zr60Al5Ni30Pd5 skeleton structure alloy was prepared by electrochemical etching treatment in its glassy phase. The nano-pore size is about 5-15 nm and no nano-phase aggregation phenomenon is recognized. The alloy composition of the nano-porous surface shifted to Zr21.8Al2.4Ni56.1Pd19.7 and the electrochemical treatment caused the enrichment of Ni and Pd elements on the nano-porous surface. The enrichment of Ni and Pd elements leads to the increases of the reaction activity with hydrogen due to Pd catalytic effect through creating diffusion pathway into the bulk of material. The nano-porous glassy alloy has homogeneous distribution of Pd element and exhibits high corrosion resistance. The hydrogen absorption/desorption characteristics cycles with enhanced kinetics are maintained without appreciable degradation up to 20 cycles and the hydrogen absorption capacity reaches about 5.4 wt%. This result indicates the possibility of developing a suitable hydrogen storage material which can reduce the consumption amount of precious Pd metals.

The Spatio-Temporal Analysis of Urban-Rural Coordinated Development and Its Driving Forces in Yangtze River Delta

This paper conducts an analytical study on the urban-rural coordinated development (URCD) in the Yangtze River Delta urban agglomeration (YRDUA), and uses data from 2000–2015 of 27 central cities to study the spatial and temporal evolution patterns of URCD and to discover the influencing factors and driving forces behind it through PCA, ESDA and spatial regression models. It reveals that URCD of the YRDUA shows an obvious club convergence phenomenon during the research duration. The regions with high-level URCD gather mainly in the central part of the urban agglomeration, while the remaining regions mostly have low-level URCD, reflecting the regional aggregation phenomenon of spatial divergence. At the same time, we split URCD into efficiency and equity: urban-rural efficient development (URED) also exhibits similar spatiotemporal evolution patterns, but the patterns of urban-rural balanced development (URBD) show some variability. Finally, by analyzing the driving forces in major years during 2000–2015, it can be concluded that: (i) In recent years, influencing factors such as government financial input and consumption no longer play the main driving role. (ii) Influencing factors such as industrialization degree, fixed asset investment and foreign investment even limit URCD in some years. The above results also show that the government should redesign at the system level to give full play to the contributing factors depending on the actual state of development in different regions and promote the coordinated development of urban and rural areas. The results of this study show that the idea of measuring URCD from two dimensions of efficiency and equity is practical and feasible, and the spatial econometric model can reveal the spatial distribution heterogeneity and time evolution characteristics of regional development, which can provide useful insights for urban-rural integration development of other countries and regions.

Reconstruction of low-rank aggregation kernels in univariate population balance equations

The dynamics of particle processes can be described by population balance equations which are governed by phenomena including growth, nucleation, breakage and aggregation. Estimating the kinetics of the aggregation phenomena from measured density data constitutes an ill-conditioned inverse problem. In this work, we focus on the aggregation problem and present an approach to estimate the aggregation kernel in discrete, low rank form from given (measured or simulated) data. The low-rank assumption for the kernel allows the application of fast techniques for the evaluation of the aggregation integral (mathcal {O}(nlog n) instead of mathcal {O}(n^{2}) where n denotes the number of unknowns in the discretization) and reduces the dimension of the optimization problem, allowing for efficient and accurate kernel reconstructions. We provide and compare two approaches which we will illustrate in numerical tests.

Aggregation and breakup of colloidal particle aggregates in shear flow: A combined Monte Carlo - Stokesian dynamics approach

A method for the simulation of aggregation and breakup processes in colloidal particle suspensions is presented. The method combines a Monte Carlo algorithm to determine, on the basis of probabilistic considerations, the sequence of aggregation and breakup events, and a Discrete Element Method, built in the framework of Stokesian dynamics and contact mechanics, to accurately reproduce them. Liquid-solid suspensions subject to a uniform shear stress are investigated. The model is seen to be able to reproduce the typical dynamic steady state which is observed in colloidal suspensions under severe shearing, in which the effects of aggregation and breakup balance each other. The structural properties of the aggregates and the dynamics of the aggregation and breakup phenomena are characterized in detail. Both fragmentation and erosion are seen to contribute to the breakup process, which is characterized by an exponent similar to the one reported in the literature for compact clusters.

Surface Minimal Bactericidal Concentration: A comparative study of active glasses functionalized with different-sized silver nanoparticles

In this work the quantification of antimicrobial properties of differently sized AgNPs immobilized on a surface was studied. Three different sizes of spheroidal AgNPs with a diameter of (6, 30 and 52) nm were synthetized and characterized with UV–vis, SEM, TEM and ICP-MS. The MIC (Minimal Inhibitory Concentration) and MBC (Minimal Bactericidal Concentration) against Escherichia coli were investigated. Then, the antibacterial efficacy (R) of amino-silanized glasses coated with different amounts of the three sizes of AgNPs were quantified by international standard ISO 22196 adapted protocol against E. coli, clarifying the relationship between size and antibacterial properties of immobilized AgNPs on a surface. The total amount of silver present on glasses with an R ∼ 6 for each AgNPs size was quantified with ICP-MS and this was considered the Surface MBC (SMBC), which were found to be (0.023, 0.026 and 0.034) μg/cm2 for (6, 30 and 52) nm AgNPs, respectively. Thus, this study demonstrates that active surfaces with a bactericidal effect at least ≥ 99.9999 % could be obtained using an amount of silver almost 100 times lower than the MBC found for colloidal AgNPs. The immobilization reduces the aggregation phenomena normally occuring in liquid media, maximizing the exposed specific superficial area of the AgNPs and their direct contact with bacterial cells. Starting from this glass model system, our work could broaden the way to the development of a wide range of antibacterial materials with very low amount of silver that can be safely applied in biomedical and food packaging fields.

Experimental and DFT studies on the effect of carbon nanoparticles on asphaltene precipitation and aggregation phenomena

• CNPs were synthesized for controlling asphaltene precipitation and aggregation. • FESEM and FTIR demonstrate uniform adsorption of asphaltene on surface of CNPs. • DFT modeling proves the strong hydrogen interaction between CNPs and asphaltenes. • CNPs represent biocompatible and affordable asphaltene inhibitor-dispersant. In this study, a new class of carbon nanoparticles (CNPs) is synthesized for inhibition/dispersion of asphaltene precipitation and aggregation in unstable crude oil. The microscopy and asphaltene dispersant experiments are carried out to assess the effects of CNPs on asphaltene precipitation and aggregation. Also, density functional theory is applied to describe the mechanisms of asphaltene adsorption onto the CNPs surfaces. Experimental results demonstrate postponement of asphaltene onset of precipitation from 26 to 37 vol% n-C 7 in the presence of 400 ppm of the CNPs which is ascribed to the extra high specific surface area of the CNPs. DLS analysis shows the average size of asphaltene aggregates adsorbed onto the CNPs reduces from 1730 nm in the blank oil to 255 nm in treated oil with CNPs. The results of DFT modeling demonstrate the strong hydrogen interaction between functional groups of the CNPs and active sites of asphaltene. Also, π–π interactions occur between electron cloud of aromatic rings of asphaltene and CNPs with minimum equilibrium distance of 2.94 Å. The adsorption energy for the most stable complex of asphaltene and CNPs in the gas and solvent phases are −91.22 and −107.64 kJ/mol, respectively, confirming the strong chemisorption of asphaltene over the CNPs. This research reveals that synthesized CNPs with specific features such as high surface area, potential of covering the external shell with a wide variety of functional groups, low toxicity and cost, and environment-friendly can be successfully implemented as an efficient inhibitor and/or dispersant for asphaltene handling strategies.

Chemical-Physical Behaviour of Microgels Made of Interpenetrating Polymer Networks of PNIPAM and Poly(acrylic Acid).

Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of a dual responsive microgel composed of poly(N-isopropylacrylamide) (PNIPAM), a temperature sensitive polymer, and poly(acrylic acid) (PAAc), a pH sensitive polymer, at different temperatures, PAAc contents, concentrations, solvents and pH. The combination of multiple techniques as Dynamic Light Scattering (DLS), Raman spectroscopy, Small Angle Neutron Scattering (SANS), rheology and electrophoretic measurements allow to investigate the hydrodynamic radius behaviour across the typical Volume Phase Transition (VPT), the involved molecular mechanism and the internal particle structure together with the viscoelastic properties and the role of ionic charge in the aggregation phenomena.

Implementation of a multilayer statistical physics model to interpret the adsorption of food dyes on a chitosan film

This paper reports the application of an advanced multilayer model to study the adsorption of food dyes FD&C blue No. 2, acid red 18, FD&C red No. 2, and FD&C yellow 5 from aqueous solutions with a chitosan film. These dyes' adsorption mechanisms were discussed and analyzed at 298–328 K and pH 4–7 via statistical physics calculations. Physicochemical parameters were utilized to explain the dye adsorption at the molecular scale. Modeling results showed dye aggregation phenomena where each functional group of chitosan film adsorbed several dye molecules simultaneously at different tested temperatures. Aqueous solution temperature reduced the dye adsorption capacities, attributed to the exothermic nature of dye removal. The chitosan film was more effective for the adsorption of dye FD&C yellow 5. The estimated adsorption energies for dye-chitosan film and dye-dye interactions confirmed an exothermic physisorption associated with van der Waals forces and hydrogen bonding. This study's results contributed to expanding the knowledge on the adsorption mechanisms of dye molecules using biopolymers like chitosan.

Noncovalent Association and Partitioning of Some Perfume Components at Infinite Dilution with Myelin Basic Protein Pseudophase in Normal Saline

Myelin basic protein (MBP), one of the major protein constituents of the myelin sheath, possesses unique ligand-binding features. We present a novel equilibrium headspace gas chromatographic technique to examine the thermodynamics of noncovalent interactions between common perfume components: Lilial, Hedione, Hexylcinnamic aldehyde, and Versalide with MBP monomers and its hexameric MBP-pseudophase. A general theoretical model is used to calculate the critical aggregation concentration (cac) of MBP, perfume component binding constants with monomeric MBP, K11, and MBP as pseudophase, Kn1, and free energies for perfume component binding with monomeric MBP, ΔGb,11, and MBP as pseudophase, ΔGb,n1. In addition, the pseudophase-water partition coefficients, Kx, the free energies of transfer of perfume from bulk water to the MBP-pseudophase, ΔGt, and the intra-aggregate activity coefficients, γm∞, at infinite dilution were also determined. The cac value measured by the method of fractional distribution is a unique and precise approach in understanding the aggregation phenomenon. Within the experimental error, the 1:1 binding free energies did not differ by more than 1 kJ/mol among the perfume components but favored the MBP pseudophase binding by 6 kJ/mol. Therefore, that protein aggregation can enhance the binding of small molecules is probably a general conclusion. While the magnitudes of K11, Kn1, ΔGb, Kx, and ΔGt show weak trends, the γm∞ values show a strong and distinct trend in interaction, spanning 4 orders of magnitude among the perfume components.

A hyperbranched polymer synthetic strategy for the efficient fixation of metal species within nanoporous structures: Application in automotive catalysis

In the present study, a novel synthetic approach, called assisted impregnation technique, is described for the production of highly active Pd monometallic three-way catalysts supported on SBA-15. The assistance in this method originates from a hyperbranched polymer (carboxy-methylated polyethyleneimine, Trilon-P), able to entrap metal ions and therefore act as a metal binding agent due to its unique chemical and chelating properties. A series of Pd / SBA-15 samples with different Pd loadings, varying from 0.13 to 3 wt%, were produced. All the as-developed materials, evaluated under simulated exhaust conditions at the stoichiometric point, exhibit an excellent CO and HC oxidation performance, providing even very high CH4 conversions at low temperatures. However, material with 3 wt% Pd loading stands out affording complete NO reduction at 300 °C. The positive effect of the employed synthetic procedure is clearly demonstrated by comparing the latter sample with its counterpart derived from conventional dry impregnation technique. As deduced by a combination of techniques, assisted impregnation technique succeeds to deliver very small highly dispersed PdO nanoparticles uniformly distributed within SBA-15 porous network, through metal-polymer complex formation. The derived PdO nanoparticles demonstrate an average size ranging between 2.1 and 2.4 nm with tight distribution and pronounced stability considering the negligible aggregation and particle growth phenomena after the catalytic reaction. On the contrary when dry impregnation is employed the size of PdO nanoparticles undergoes a two-fold increase from approximately 3 to 6 nm upon exposure at automotive exhaust conditions.

Prolonged activity of a recombinant manganese superoxide dismutase through a formulation of polymeric multi-layer nanoassemblies targeting cancer cells

A new isoform of human manganese superoxide dismutase (SOD) has been recently isolated and obtained in a synthetic recombinant form and termed rMnSOD. As compared to other SODs, this isoform exhibits a dramatically improved cellular uptake and an intense antioxidant and antitumoral activity. Unfortunately, its use is severely hampered as this active pharmaceutical ingredient (API) in solution suffers from remarkable instability, which realizes as an interplay of unfolding and aggregation phenomena. This leads the API to be ineffective after three weeks only when stored at 4°C.A formulation strategy was undertaken to mitigate this instability. This was based on the incorporation of the API in hyaluronic acid and its layer-by-layer deposition over a chitosan-n-acetyl cysteine- monolayer nanoemulsion (NE) and its subsequent coverage with a further external interface of a chitosan-n-acetyl cysteine. The obtained constructs were tested over a selected panel of healthy and cancerous cell lines. The undertaken formulation strategy enhanced the API's effect in vitro already at time zero, maintaining the efficacy of this anticancer agent until up to 30 weeks when stored at 4°C.