Increasing Bulk Concentration Research Articles

Revealing the Origin of Cooperative Adsorption of Chains on Nanoparticle Surfaces through Coarse-Grained Simulations.

This work aims to deepen our understanding of the molecular origin of the recently observed phenomenon of polymer cooperative adsorption onto faceted nanoparticle (NP) surfaces. By exploring a large parameter space for polymer/NP interactions through coarse-grained (CG) molecular dynamics (MD) simulations, it is found that consistent with experiments the presence or absence of cooperativity is related to solvent quality and relative interaction strengths between the polymer and the adsorbent. Specifically, positive cooperativity is associated with stronger polymer-polymer interaction than polymer-surface interactions and vice versa for negative cooperativity. This contrast in interaction energies manifests in positive cooperativity (i.e., increased affinity) and negative cooperativity (i.e., decreased affinity) as concentration increases. It is also found that increasing chain length strengthens cooperativity effects and that the nanoscale confinement of polymer chains to the adsorbing facet (due to weaker affinity to corners and edges) enhances positive cooperativity but weakens negative cooperativity. Moreover, adsorption onto a spherical NP shows stronger positive cooperativity but weaker negative cooperativity compared with adsorption onto a cubic NP of equal surface area. It was further found that as polymer bulk concentration increases, the free energy of adsorption decreases in positive cooperativity, increases in negative cooperativity, and is independent of concentration in noncooperative systems consistent with the phenomenological explanation of cooperativity. We further found that positive cooperativity is associated with growing fluctuations in the adsorption density at critical bulk polymer concentrations. This behavior can be attributed to the competition between enthalpic gains and entropic losses upon adsorption. Overall, our results shed light on the microscopic origin of cooperative adsorption and the role of solvent quality, which can be leveraged in, for example, controlling NP growth into target shapes and designing NP catalysts with improved performance.

Mechanistic Insights into Propylparaben Sorption on Polyvinyl Chloride

The mechanism of loss of propylparaben potency from formulations when in contact with polyvinyl chloride has been determined. It is caused by the adsorption of propylparaben onto polyvinyl chloride surfaces. The adsorption kinetics is best described using a pseudo-second order model based on non-linear fit. The rate of adsorption increases with increasing bulk concentration of propylparaben. Adsorption equilibrium isotherm was fitted to three isotherm models: Langmuir, Freundlich, and Temkin, using non-linear fit. The Freundlich and Temkin models show the best fit, indicating a multi-layer adsorption. Using this case study, we present a methodology to provide mechanistic insights into the compatibility data between pharmaceutical ingredients and product contact materials when sorption is involved.

Quasi-steady-state modelling and characterization of diffusion-controlled dissolution from polydisperse spheroidal particles, II: characterization

A quasi-steady-state model for accurately predicting the detailed diffusion-dominated dissolution process of polydisperse spheroidal (prolate, oblate and spherical) particle systems was presented in Part I of this study. In the present paper, the dissolution characteristics of typical polydisperse spheroidal particle systems have been extensively investigated. The effects of the distributions of particle size and shape have been studied by examining the detailed dissolution processes, such as the size reduction rates of individual particles, the increase in bulk concentration and the dissolution time of the polydisperse systems. Some important factors controlling the dissolution process, including initial particle concentration, smallest and largest particle sizes, and the smallest and largest Taylor shape parameters, have been identified.

Quasi steady-state modelling and characterization of diffusion-controlled dissolution from polydisperse spheroidal particles, I: modelling

A quasi steady-state model (QSM) for accurately predicting the detailed diffusion-dominated dissolution process of polydisperse spheroidal (prolate, oblate and spherical) particle systems with a broad range of distributions of particle size and aspect ratio has been developed. A rigorous, mathematics-based QSM of the dissolution of single spheroidal particles has been incorporated into the well-established framework of polydisperse dissolution models based on the assumption of uniform bulk concentration. Validation against experimental results shows that this model can accurately predict the increase in bulk concentration of polydisperse systems with various particle sizes and shape parameters. A series of representative instances involving the dissolution of polydisperse felodipine particles at various concentration ratios is used to demonstrate the model's effectiveness, rendering it a valuable tool for understanding and managing complex systems with diverse particle characteristics.

Electrokinetic energy conversion in the nanochannel coupled with surface charge and slip effects

Inspired by the universal phenomena in nature and advances in nanotechnology, the ion transport in nanochannel receives increasing attention and shows great promising in energy conversion. The precedent studies generally predicted the ion transport by tuning the single physical parameter, the understanding of ion dynamics in the real multi-physical coupling systems is still scarce. Here, an ion transport model coupled with surface charge and slip effects is proposed to investigate the energy conversion behavior in nanochannel. The results show that the surface charge density increases with the increasing bulk concentration, nanochannel size and solution pH. The original boundary slip tends to decrease the surface charge density and the surface charge in turn reduces the boundary slip significantly, which manifests the strong coupling effect of diverse factors. The output power and energy conversion efficiency increases first and then decrease with the increasing bulk concentration and pH. The increase of channel size is beneficial for promoting output power, but unfavorable on energy conversion efficiency. More important, the boundary slip greatly enhances the output power and energy conversion efficiency, leading to a maximum output power and energy conversion efficiency is 2.7 pW and 30%, respectively. As a proof of concept, this work shows the distinct deviation in power generation in ion nanochannel with the constant and dependent physical property, providing the useful information to guide the design of real fluidic energy devices.

Interfacial Dilational Rheology of Molecular Films in DC Electric Fields.

We present a novel technique to measure the interfacial dilational rheology of a molecular film adsorbed at a water-oil interface in a direct-current (dc) electric field. A film of a highly polar subfraction of asphaltenes was allowed to adsorb at a water drop interface, surrounded by an organic phase and subjected to a dc electric field. The measurements involved calculations of the dynamic interfacial tension (IFT), while the drop was sinusoidally oscillated, using our in-house axisymmetric drop shape analysis (ADSA) algorithm adapted for electric fields. The amplitude of the IFT waveform over equilibrium IFT and the phase difference from the applied area oscillations were used in the estimation of surface moduli. The asphaltene films were found to become more elastic on increasing bulk concentrations and electric field strengths. However, the effect was not monotonous and observed to be governed by combinations of these parameters. The Lucassen-van den Tempel (LVDT) model was used to further elucidate the experimentally obtained interfacial dilational moduli.

The retention of multivalent pollutants in mineral layers

Radioactive waste treatment is earning worldwide awareness due to the harmful impact of radiation emitted from these wastes to human health and environment. Clay can be used as effective adsorbent in order to remove radioactive pollutants in aqueous solution, and have great potential for ion exchange technique. In our study we investigated the montmorillonite clay using primitive model Grand canonical Monte Carlo (MC) simulations to describe the ion exchange or competition between the counterions of different valences. Throughout the study we introduced a formula representing the retention coefficient to quantify the ion exchange, which is essentially proportional to the more common distribution coefficientKd, and has the advantage of being dimensionless and more suitable for theoretical cases. we emphasized on the effect of surface charge density of clay platelets assumed to be negative, valence of the pollutants, and ground water reservoir concentrations of pollutants and of other cations. It is found that the retention is increased by increasing the valence of the pollutants, and the surface charge density, while it is decreased by increasing bulk concentration of pollutants and of other cations. Also it is found that the presence of high concentration of monovalent is less serious for the retention than the presence of multivalent ones.

Reclined trend of alkyl chain of sodium dodecylbenzenesulfonate molecules induced by friction

Surfactants tend to adsorb on the surface/interface mostly in a directional manner. The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate (SDBS) at low concentrations are studied by using the sum frequency generation vibrational spectroscopy (SFG-VS). The molecular arrangement of the surfactants adsorbed at the solid/liquid interface is further investigated. It is found that the arrangement of the SDBS at the interface becomes relatively ordered with increasing bulk concentration. Meanwhile, the orientation angle reduces gradually, and the molecules tend to be upright state. In addition, the effect of friction on the conformation order and orientation angle are also analyzed. The intensity of the SDBS vibrational contraction peak becomes lower after friction, which indicates that the anion has a reorientation process at the interface. The arrangement of molecules becomes more disordered due to friction. The orientation angle increases slightly, which indicates the monolayer has an inclined trend relative to the lateral direction on the interface. A modified adsorption model considering friction effect is proposed. This work may provide a reference for the further study of adsorption mechanism and application of surfactants.

Surfaces Affect Screening Reliability in Formulation Development of Biologics.

The ability to predict an antibody's propensity for aggregation is particularly important during product development to ensure the quality and safety of therapeutic antibodies. We demonstrate the role of container surfaces on the aggregation process of three mAbs under elevated temperature and long-term storage conditions in the absence of mechanical stress. A systematic study of aggregation is performed for different proteins, vial material, storage temperature, and presence of surfactant. We use size exclusion chromatography and micro-flow imaging to determine the bulk concentration of aggregates, which we combine with optical and atomic force microscopy of vial surfaces to determine the effect of solid-liquid interfaces on the bulk aggregate concentration under different conditions. We show that protein particles under elevated temperature conditions adhere to the vial surfaces, causing a substantial underestimation of aggregation propensity as determined by common methods used in development of biologics. Under actual long-term storage conditions at 5°C, aggregate particles do not adhere to the surface, causing an increase in bulk concentration of particles, which cannot be predicted from elevated temperature screening tests by common methods alone. We also identify specific protein - surface interactions which promote oligomer formation in the nanometre range. Special care should be taken when interpreting size exclusion and particle count data from stability studies if different temperatures and vial types are involved. We propose a novel combination of methods to characterise vial surfaces and bulk solution for a full understanding of protein aggregation processes in a sample.

Diagenetic formation of bedded chert: Implications from a rock magnetic study of siliceous precursor sediments

Bedded chert is a distinctive rock type characterized by a rhythmic alternation of quartz-rich chert beds and clay-rich interbeds. The origin of the lithologic variations is not well understood. A rock magnetic study of a sequence of alternating bands of radiolarian-rich and clay-rich bands recovered by ODP leg 129, which is considered to be the best-known analog for the bedded chert precursor sediments, shows that the relative abundances and characteristics of magnetic phases are similar in both sediment types, with only a minor (1.5 times on average) increase in bulk concentration in clay-rich bands. Comparison with magnetic properties of the diagenetically mature chert-shale couplets suggests that siliceous precursor sediments undergo strong differential diagenetic modification. A simple silica transfer model, with dissolution of silica in proto-shale donor beds and deposition in proto-chert receiver beds, indicate that the known features of the bedded chert sequences, such as the difference in thickness, cosmic dust content between chert and shale, can be reproduced in case of donor beds having initially lower clay (higher biogenic silica) content compared to receiver beds. While contrary to the current depositional model explaining chert beds formation by episodic radiolarian bloom on a background of slow accumulation of clays, an association of proto-shale beds with high productivity episodes is supported by an independent paleoproductivity proxy – their higher Al/Ti values, and is in full agreement with the known silica diagenesis trends, particularly, with the retarding influence of detrital minerals on silica transformations. The impetus for diagenetic silica segregation is provided by initial variability in clay content within a siliceous sedimentary succession. Silica dissolution starts in clay-poor intervals. When diffusing silica encounters clay-rich beds, adsorption to clay lowers dissolved silica content below the saturation level of the higher solubility phases and leads to deposition of low solubility quartz. Early deposition of quartz cement prevents significant compaction of chert layers, while the loss of silica in donor beds leads to their compaction and concomitant increase in non-reactive clay and cosmic dust particles. Severe distortion of primary environmental signals during differential diagenesis questions the use of bedded chert sequences for cyclostratigraphic studies.

Effect of Mn and Cr on the selective oxidation, surface segregation and hot-dip Zn coatability

The effect of Mn and Cr on the surface selective oxidation, segregation and hot-dip galvanizing was studied in three Fe-Mn alloys with ∼0.2 wt% Al and two Fe − Mn alloys with ∼0.5 wt% Cr in an HDPS (Hot-dip Process Simulator) following industrial CGL (Continuous Galvanizing Line) conditions. The Mn content was varied from 1.5 to 3.6 wt% in the alloys. The alloys were subjected to the same thermal cycle following continuous annealing (CA) at 800 °C in N2 − 5%H2 gas atmosphere with −40 °C dew point and then hot-dipping in Zn - 0.20 wt% Al bath at 460 °C. The oxidation tendency of Mn, Al and Cr during annealing was calculated using FactSage software. GDOES (Glow Discharge Optical Emission Spectroscopy) measurements showed a higher extent and depth of segregation for Mn with increasing bulk concentration during the CA. It was observed that Cr segregates comparatively less near the annealed surface in the presence of more Mn. XPS (X-ray Photoelectron Spectroscopy) measurements revealed the formation of simple MnO in Fe-Mn-Al alloys and complex MnCr2O4 in Fe-Mn-Cr alloys. Contrary to the thermodynamic calculations, no Al-oxides were detected at the annealed surfaces of Fe-Mn-Al alloys during the XPS study. The hot-dip Zn coatability was determined by measuring the number density of uncoated spots using 3D CLSM (Confocal Laser Scanning Microscopy) and by visual inspection. The Fe-Mn-Cr alloys displayed a better hot-dip Zn-coating compared to Fe-Mn-Al alloys. The conclusions of the present study are also critically discussed considering the literature findings.

Interfacial Dilational Rheology of Sodium Lauryl Glycine and Mixtures with Conventional Surfactants

AbstractAmino acid‐based surfactants are environmentally friendly surfactants, which have aroused increasing interest. In the application of amino acid‐based surfactants, they are often compounded with other kinds of surfactants to obtain formulations that meet certain requirements. Herein, sodium lauroyl glycinate (C12‐Gly‐Na) was selected as a representative amino acid‐based surfactant to compound with an anionic surfactant (sodium dodecyl sulfate [SDS]), a cationic surfactant (dodecyl trimethyl ammonium Bromide), and a nonionic surfactant (Triton X‐100: p‐octyl polyethylene glycol phenyl ether). Surface tension measurements and interfacial dilational rheological experiments were performed to study the interfacial behaviors of C12‐Gly‐Na and its mixtures. The results show that mixture systems have better interfacial activity than individual C12‐Gly‐Na and there is an obvious synergy between C12‐Gly‐Na and C12TAB under strong electrostatic attraction. Thus, the C12‐Gly‐Na/C12TAB mixture shows lower critical micelle concentration (CMC) and γCMC and higher dilational modulus than the individual surfactants. Besides, the film formed by the C12‐Gly‐Na/C12TAB mixture has higher viscoelasticity than single C12‐Gly‐Na and its mixtures with SDS and TX‐100. With the increase of bulk concentration, the dilational moduli of C12‐Gly‐Na, C12‐Gly‐Na/SDS, and C12‐Gly‐Na/TX‐100 run through two maxima, while, due to stronger electrostatic attraction, only one maximum appears in the C12‐Gly‐Na/C12TAB system. The study of the interfacial properties of amino acid surfactant and its mixtures with other surfactants provides a theoretical foundation for potential applications in cosmetic, food processing, and daily chemical industries.

Sonochemical Degradation of Benzothiophene (BT) in Deionized Water, Natural Water and Sea Water.

This paper deals with the sonochemical water treatment of polycyclic aromatic sulfur hydrocarbons (PASHs), one of the most common impurities found in waste water coming from petroleum industry. The best fit of the experimental data appears to be the kinetic parameters determined using the Michaelis-Mentonmodel in the concentrations range of the study. For the initial increase in the degradation rates, it is simply considered that the more the bulk concentration increases, the more the concentration in the interfacial region increases. This will be explained by Michaelis-Menton kinetics. The influence of organic compounds in the water matrix as a mixture with Benzothiophene (BT) was also evaluated. The results indicated that BT degradation is unaffected by the presence of bisphenol A (BPA). Finally, the results indicated that ultrasonic action is involved in oxidation rather than pyrolitic processing in the BT sonochemical degradation.

Wettability of a polymethylmethacrylate surface in the presence of benzyl-substituted alkyl betaines

The adsorption and wettability of benzyl substituted alkyl carboxylbetaine (BCB) and alkyl sulfobetaine (BSB) at polymethylmethacrylate (PMMA) surfaces have been studied by contact angle measurements and the adsorption parameters such as adhesional tension, adsorption amount, work of adhesion and PMMA-liquid interfacial tension (γSL) have been calculated. The results show that the values of contact angle of betaines keep constant before CMC, which can be explained well by the compensation effect of the decrease of surface tension and increase of γSL with an increase of bulk concentration. However, only the contact angle of BCB solution begins to decline when the concentration is far higher than CMC, indicating the re-adsorption. Both the hydrophilic head and benzyl of BCB molecules interact with PMMA surface, which decreases adsorption amount but improves ability of hydrophobic modification for PMMA. On the other hand, the benzyl may trend to stretch towards aqueous for BSB, instead of interacting with PMMA, because of the steric effect of larger hydrophilic head of BSB. The unique arrangement of BSB molecules at PMMA surface makes it difficult to re-adsorb onto monolayer at higher bulk concentration.

Fabrication of Supramolecular Chirality from Achiral Molecules at the Liquid/Liquid Interface Studied by Second Harmonic Generation

We present the investigation into the supramolecular chirality of 5-octadecyloxy-2-(2-pyridylazo)phenol (PARC18) at water/1,2-dichloroethane interface by second harmonic generation (SHG). We observe that PARC18 molecules form supramolecular chirality through self-assembly at the liquid/liquid interface although they are achiral molecules. The bulk concentration of PARC18 in the organic phase has profound effects on the supramolecular chirality. By increasing bulk concentration, the enantiomeric excess at the interface first grows and then decreases until it eventually vanishes. Further analysis reveals that the enantiomeric excess is determined by the twist angle of PARC18 molecules at the interface rather than their orientational angle. At lower and higher bulk concentrations, the average twist angle of PARC18 molecules approaches zero, and the assemblies are achiral; whereas at medium bulk concentrations, the average twist angle is nonzero, so that the assemblies show supramolecular chirality. We also estimate the coverage of PARC18 molecules at the interface versus the bulk concentration and fit it to Langmuir adsorption model. The result indicates that PARC18 assemblies show strongest supramolecular chirality in a half-full monolayer. These findings highlight the opportunities for precise control of supramolecular chirality at liquid/liquid interfaces by manipulating the bulk concentration.

Foam stabilized by large casein micelle aggregates: The effect of aggregate number in foam lamella

In this study, a casein micelle aggregate dispersion (CMAD) with average particle size of 6.7 ± 0.5 μm was prepared using ultracentrifugation, pelleting, milling and redispersion and mixed with a casein micelle dispersion (CMD) with average particle size of 0.13 ± 0.02 μm in varying ratios (0, 25%, 50%, 75% and 100% CMAD, v/v). The effect of particle concentration and size of casein micelle aggregates (CMAs) on foam stability and thin film stability was investigated. Results showed that foam stability increased with increasing bulk concentration of CMAs. The actual aggregate concentration in foam lamella which account for an improved foam stability was well quantified using optical microscopy. Besides, the thin film measurements showed an increase in film rupture times with increasing aggregate concentration in the thin films for diluted dispersions, which confirmed the strong link between aggregate number in foam lamella and corresponding foam stability. At the protein concentration studied (2%), the aggregates did not form a gel network in the lamella but were randomly distributed over the film. The film and foam stabilization by CMAs is ascribed to the fact that they effectively divided the whole film into film elements with smaller radius, resulting in a smaller critical film thickness for film rupture. Another effect is that film drainage can be slowed down by an effective suction pressure in the film due to the curvatures induced by the wetting of hydrophilic particles. In conclusion, aggregated particles of casein micelles around 5–10 μm prepared in this research could be applied to enhance the functional properties of dairy foams.

Effect of poly-dispersed nanostructures on concentration polarization phenomena in ion exchange membranes

We investigated the effect of poly-dispersed nanostructures on concentration polarization (CP) phenomena in ion exchange membranes through fabrication of poly-dispersed interconnecting channels (Pd-ICs) integrated microfluidic chip and characterized the CP phenomena which happens near the interconnecting channel and main microchannel interface. Current-voltage (I-V) characteristics and depletion (enrichment) layer formation behavior within Pd-IC system are examined. We found that “Electric field focusing” affects the I-V characteristics of Pd-IC system, and Pd-IC system follows the “Limiting current occurrence” criterion. The visualization results show that the depletion layer thickness at the anodic side decreases with an increasing dispersity and also for increasing bulk concentration. We attribute this phenomena to the high electroosmotic flow in the sub-microchannel and “Electroosmosis of the second kind” at the electrolyte-membrane (Pd-IC) interface. The perm-selectivity of interconnecting channels also play an important role. At the cathodic side, we observed that fluorescent dye depleted at the microchannel and sub-microchannel interface due to the ejecting flow and current balance at the corner wedge of sub-microchannels. We hope these working mechanisms of Pd-IC system to be beneficial to model pseudo-ion exchange membrane and to develop high efficiency ion exchange membranes.

Analysis of Diffusion-Controlled Dissolution from Polydisperse Collections of Drug Particles with an Assessed Mathematical Model

We introduce a "hierarchical" modeling strategy designed to be systematically extensible to increase the detail of dissolution predictions from polydisperse collections of drug particles and to be placed on firm mathematical and physical foundations with diffusion-dominated dissolution at its core to predict dissolution and the evolution of particle size distribution. We assess the model with experimental data and demonstrate higher accuracy by treating the polydisperse nature of dissolution. A level in the hierarchy is applied to study elements of diffusion-driven dissolution, in particular the role of particle-size distribution width with varying dose level and the influences of "confinement" on the process of dissolution. Confinement influences surface molecular flux, directly by the increase in bulk concentration and indirectly by the relative volume of particles to container. We find that the dissolution process can be broadly categorized within three "regimes" defined by the ratio of total concentration Ctot to solubility CS . Sink conditions apply in the first regime, when C tot /CS<∼0.1. When C tot /CS>∼5 (regime 3) dissolution is dominated by confinement and normalized saturation time follows a simple power law relationship. Regime 2 is characterized by a "saturation singularity" where dissolution is sensitive to both initial particle size distribution and confinement.

Study on Metal Chelation Adsorption of NO Using Fe(II)EDTA Solution in Power Plant

The influences of concentration of metal chelation solution, pH values, the concentration of O2 supplied by some thermal power plants in Wuxi, and the concentration of SO32- on the adsorption performance were studied. The results indicated that the removal ratio improved with the increase of bulk concentration. However, when the concentration exceeded 15mmol/L, the increase rate reduced. It was found that the chelation ability enhanced with the increase of pH values as well as the decrease of oxygen concentration in the flue gas. The SO32- in the solution was beneficial to improve and extend the adsorption capacity of Fe (II) EDTA. According to the FI-IR, the carboxyl in Na2EDTA coordinated with Fe(II). XPS showed that Fe2+ was the main valence of Fe in Fe(II)EDTA. Through the calculation of fold peak area, the content of Fe2+ was 72.17%. And the existence of Fe2+ in the Fe(II)EDTA was pivotal for the complexation.

Investigation on post annealed copper sulfide thin films from photochemical deposition technique

CuxS thin films were deposited on glass substrates at room temperature by photochemical deposition after 1h photo irradiation using the precursor solution containing copper sulphate pentahydrate (CuSO4·5H2O), sodium thiosulphate (Na2S2O3) as a source material for Copper and Sulphur respectively and Di Sodium salt of EDTA as a chelating agent in acidic medium (pH~3.0). The as deposited and annealed CuxS thin films were investigated using XRD, UV–vis, AFM, SEM and Hall measurements. The deposited thin films were annealed at temperature up to 400°C for 1h. Above 200°C the deposited film of CuxS changes from anilite phase (Cu1.75S) to digenite (Cu1.8S) phase. The reduction in sulphur content of the films is evident in the EDX analysis. From the Hall Effect results as deposited and annealed films show p-type conductivity with increasing bulk concentration. Analyses of the optical bandgap of the films indicate an indirect bandgap between 1.75 and 2.35eV.