Concentrated Dispersions Research Articles

NMR proton relaxation for measuring the relative concentration of nanoparticles in liquids.

The measurement of relative concentration of nanoparticles in liquids has been investigated using NMR proton relaxation, addressing a gap in analytical capabilities for highly concentrated dispersions. This technique has a limited footprint, short measurement time and ease of operation making it a promising quality control method to support the development and manufacture of nanomaterials.

Polyvinyl Alcohol/Pectin-Based Hydrogel as Sorptive Phase for the Determination of Freely Dissolved Parabens in Urine Samples by LC-DAD

An extraction phase based on hydrogel disks of polyvinyl alcohol and pectin was developed, characterized, and evaluated for the extraction of four endocrine disruptors (methylparaben, ethylparaben, propylparaben and butylparaben) in free form in human urine samples with subsequent determination by liquid chromatography coupled with a diode array detector (LC-DAD). The proposed hydrogel showed easy synthesis, was made of low-cost and non-toxic polymers, and showed that it has an amphiphilic character. Gels with lower swelling indexes (175%) and more concentrated dispersions of polymers (P20PC2.0) showed lower relative standard deviation (RSD) values. Under optimized solid phase extraction (SPE) conditions, the LC-DAD method presented limits of quantification of 0.1 µg mL-1, accuracy values ranged from 101.3 to 118.2%, while the inter-assay precision ranged from 1.5 to 17.4%. In addition, the polyvinyl alcohol (PVOH)/pectin-based material presented the possibility of reuse of at least 15 times, without presenting carryover effect and physical degradation. In this way, the hydrogel shows promise for the extraction of organic compounds with different polarities in biological matrices.

Single-particle dispersion of carbon dots in the nano-hydroxyapatite lattice achieving solid-state green fluorescence.

Carbon dots (CDs), as new carbon nanomaterials, have potential applications in multiple fields due to their superior optical properties, good biocompatibility, and easy preparation. However, CDs are typically an aggregation-caused quenching (ACQ) material, which has a huge limitation on the practical application of CDs. To solve this problem, in this paper, CDs were prepared by the solvothermal method using citric acid and o-phenylenediamine as precursors and dimethylformamide as solvent. Then using CDs as nucleating agents, solid-state green fluorescent CDs were synthesized by in situ growth of nano-hydroxyapatite (HA) crystals on the surface of CDs. The results show that CDs are stably dispersed single-particlely in the form of bulk defects in the nano-HA lattice matrices with a dispersion concentration of 3.10%, and solid-state green fluorescence of CDs is achieved with a stable emission wavelength peak position near 503 nm, which provides a new solution to the ACQ problem. CDs-HA nanopowders were further used as LED phosphors to obtain bright green LEDs. In addition, CDs-HA nanopowders showed excellent performance in cell imaging (mBMSCs and 143B) applications, which provides a new scheme for further applications of CDs in the field of cell imaging and even in vivo imaging.

Study of 211Bi and 211Pb Recoils Release from 223Ra Labelled TiO2 Nanoparticles

Nanoparticles of various materials were proposed as carriers of nuclides in targeted alpha particle therapy to at least partially eliminate the nuclear recoil effect causing the unwanted release of radioactive progeny originating in nuclear decay series of so-called in vivo generators. Here, we report on the study of 211Pb and 211Bi recoils release from the 223Ra surface-labelled TiO2 nanoparticles in the concentration range of 0.01-1 mg/mL using two phase separation methods different in their kinetics in order to test the ability of progeny resorption. We have found significant differences between the centrifugation and the dialysis used for labelled NPs separation as well as that the release of 211Pb and 211Bi from the nanoparticles also depends on the NPs dispersion concentration. These findings support our previously proposed recoils-retaining mechanism of the progeny by their resorption on the NPs surface. At the 24 h time-point, the highest overall released progeny fractions were observed using centrifugation (4.0% and 13.5% for 211Pb and 211Bi, respectively) at 0.01 mg/mL TiO2 concentration. The lowest overall released fractions at the 24 h time-point (1.5% and 2.5% for 211Pb and 211Bi respectively) were observed using dialysis at 1 mg/mL TiO2 concentration. Our findings also indicate that the in vitro stability tests of such radionuclide systems designed to retain recoil-progeny may end up with biased results and particular care needs to be given to in vitro stability test experimental setup to mimic in vivo dynamic conditions. On the other hand, controlled and well-defined progeny release may enhance the alpha-emitter radiation therapy of some tumours.

Convertible Thermal Meta-Structures via Hybrid Manufacturing of Stereolithography Apparatus 3D Printing and Surface Metallization for Thermal Flow Manipulation

For manipulating heat flow according to human desire, thermal metamaterial structures (meta-structures) have attracted growing interest. Based on the transformation thermotics and the effective medium approximation theory, we designed and fabricated a convertible thermal meta-structural device to demonstrate that multiple different heat-flow manipulations could be conducted using a single thermal meta-structural device. The convertible meta-structures were designed by discretizing a two-dimensional plane and separating multiple square unit modules with stripe-shaped dissimilar materials of the Polydimethylsiloxane (PDMS) and solid resin with surface metallized copper (Cu). The convertible thermal meta-structure device with a relatively high geometric accuracy was fabricated via a proposed hybrid manufacturing path of "Stereolithography Apparatus (SLA) 3D printing-electroless plating-electroplating-thermally insulated packaging". The thermal manipulation features were numerically simulated and preliminarily verified by experimental testing. Using multiple dispersed square unit modules to replace an annular region of the thermal meta-structure exhibited different thermal flow functions, including thermal cloak, thermal concentration, thermal rotation, and thermal dispersion, through the unique geometric design of the heat-flow transfer direction within each module. By rotating each square unit module at a specific angle and arranging the modules, similar to a "jigsaw puzzle", the convertibility among different thermal manipulation functions was achieved. This path is anticipated to provide a new strategy for multifunctional meta-structures in thermo-physics and its potential engineering applications.

Workplace Violence in the Health Sector: Focus on the Argentinean context

Workplace violence is classified according to the focus of analysis: type of aggression (physical, psychological, and sexual) and according to the perpetrator (internal violence, if it is a member of the organization and external when it is a user or his/her companions). The impact on the worker's health is severe; the psychological damage is the first to be registered, with all the progressive symptoms of stress: cognitive disorders - loss of immediate memory, dispersion of attention and concentration, permanent state of alertness, self-reproach, anguish, depression, exhaustion, sensation of unreality, fantasies of annihilation, fragmentation of identity, sleep disorders and conflict with affective relationships and bonds of belonging. The studies analyzed show that the effects of aggression are varied and will depend on the frequency and severity of the episodes and the vulnerability caused by the number of episodes, which cause deterioration in the quality of care, suffering, and illness of those involved, thus affecting not only the personnel involved but also having repercussions on their families and the environment outside the workplace. Therefore, it is essential to investigate and analyze the factors involved in the different situations that arise and thus be able to intervene promptly. Statistics show that violence is more frequent the younger the staff is and more frequent in the case of women. It is also evident that not only age and sex are the factors that have the most significant impact on acts of violence, but other variants, such as nationality, place of work, and position held, influence the moment of being victims of aggression in the work environment.

Synthesis of phase change microcapsules based dispersants for waterborne coatings and their effects on paint film properties

The hyperdispersant SSS-MPEGA-MA (SMM) is prepared through aqueous polymerization using sodium p-styrenesulfonate (SSS), polyethylene glycol monomethyl ether acrylate (MPEGA) and maleic anhydride (MA) as monomers for dispersing phase change microcapsules (PCM). It is also concluded that the best dispersion effect is achieved when the starting concentration of SMM dispersant in aqueous solution with a solid content of phase change microcapsules of 20% occupies 2% of PCM content. The phase change microcapsules are added to a waterborne varnish with a solid content of 20%, and after adding a certain mass of SMM dispersant dropwise, phase change performance is still found on the film, which is the best with a dispersant concentration of 2%. At the same time, the hyperdispersant SMM can make the phase change microcapsules evenly distributed on the water-based varnish, and the dispersion effect is good without affecting the properties of the paint film itself.

Fabrication and characterization of nanoemulsions for encapsulation and delivery of vitexin: antioxidant activity, storage stability and in vitro digestibility.

Nanoemulsions were prepared as an encapsulation and delivery system for vitexin, a poorly water-soluble antioxidant. This study evaluated how the type and concentration of the dispersed oil phase and vitexin loading impacted droplet characteristics and nanoemulsion stability. The influences of storage temperature on antioxidant activity and in vitro gastrointestinal digestion on nanoemulsion stability were also investigated. Nanoemulsions prepared at different dispersed oil concentrations showed diverse characteristics and stability. Highest stability against droplet aggregation and phase separation with small oil droplets (< 150 nm) was observed for nanoemulsions prepared using 300 g kg-1 medium-chain triglyceride oil. These nanoemulsions are able to entrap and deliver vitexin with high encapsulation efficiency (88-90%) with no significant effect on emulsion stability. Vitexin-loaded nanoemulsions were stable during storage when refrigerated (4 °C) and at room temperature (25 °C) for up to 45 days with no effect on their antioxidant activity. Significantly delayed lipolysis rate and decreased extent of lipid digestion were observed in vitexin-loaded nanoemulsions. Stable vitexin-loaded nanoemulsions were successfully produced by high-pressure homogenization using a mixture of Tween 80 and lecithin as emulsifiers. Vitexin-loaded nanoemulsions stabilized with a mixture of these two emulsifiers were effective in retaining antioxidant activity during storage and protecting vitexin from changes during gastrointestinal digestion. Our results suggested that nanoemulsions were effective vitexin delivery systems for food applications. © 2022 Society of Chemical Industry.

Spatiotemporal dynamic evolution and influencing factors of family farms in urban agglomerations in the middle reaches of the Yangtze River

Family farms, considered the most desirable form of Chinese agriculture, play a pivotal role in promoting rural revitalization and agricultural modernization. The purpose of this study was to summarize the spatiotemporal evolution characteristics and influencing factors of family farms to better promote the development of modern agriculture. Using provincial demonstration family farms in the urban agglomeration in the middle reaches of the Yangtze River (MYR-UA) as the research object, this study applied the nearest neighbor index, kernel density analysis, multiscale spatial clustering analysis (Ripley’s K-function), and geographically weighted regression (GWR) model to reveal the spatiotemporal dynamic evolution and influencing factors of family farms. The results indicate that: 1) from 2013 to 2021, family farms exhibited annual increases, and their development stages could be divided into rapid, stable, and slow growth periods. 2) The spatial agglomeration pattern of family farms was significant, and the intercepted points at different time periods show the distribution characteristics of the entire dispersion and local concentration. The spatial evolution characteristics of different types of family farms are nearly consistent with those of the overall family farms. 3) The overall family farms and various types of family farms show a scale effect, which first strengthens and then weakens with the change in geographical distance. 4) The spatial pattern of family farms in MYR-UA is affected by both natural and social factors, of which, social factors had the greatest influence. Finally, based on the findings of the study, policy recommendations for promoting the high-quality development of family farms are proposed.

Antibacterial Properties of Ag&lt;sub&gt;3&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt; Particles on Bacteriostatic Behavior of &lt;i&gt;Escherichia coli &lt;/i&gt;

The aim of this work was to investigate the influences of different concentrations of Ag3PO4 aqueous dispersion by measuring the bacteriostatic characteristic against bacteria E. coli. The Ag3PO4 particles were successfully synthesized by precipitation method. Then, the morphological, structural and chemical compositional analyses were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. All these analyses confirmed the formation of Ag3PO4 particles with the shape of nearly spherical with a size of 100 – 700 nm. Meanwhile, Kirby-Bauer disk diffusion susceptibility test was chosen to determine the sensitivity of E. coli to antibacterial compounds in Ag3PO4 particles. The results showed that the antibacterial ability was significantly improved by increasing the concentration of Ag3PO4 aqueous dispersion, and the best concentration was 600 mg /mL. This study suggested that Ag3PO4 particles can be exploited as an effective candidate for antibacterial agents.

Towards improved performance of waterborne polymer dispersions through creation of dense ionic interparticle network within their films

To overcome the main challenge of low performance of the waterborne polymer coatings due to the particulate nature of the polymer dispersions and the complex film formation process, in this work we implemented the strategy of ionic complexation between oppositely charged waterborne polymer particles. For that aim, doubled charged ionic monomers ithaconic acid (IA) and styrenic 1,4-diazabicyclo[2.2.2]octane (DABCO) were used to densely functionalize (meth)acrylic film forming polymer particles, synthesized by seeded semi-batch emulsion polymerization to produce high solids content anionically and cationically charged polymer dispersions, respectively. The main advantage of the double charges in the selected ionic monomers is that they provide high ionic charge density onto charged particles at lower content of ionic monomers.The blending of these oppositely, densely charged and concentrated dispersions resulted in instantaneous coagulation. To postpone the immediate complexation, water-soluble non-ionic polymeric stabilizing species as steric obstacles around the colloids were employed, which allowed to prepare colloidally stable blends and to prepare ionic complexed films. Certainly, the established ionic complexes between carboxylic acids of IA anionic monomer and quaternary ammonium groups of DABCO units within the films improved substantially the mechanical properties and the water sensitivity of the ionic complexed polymeric films with respect to individual films and the reference blend, in which ionic bonding was prevented by pH control. Moreover, the dense ionic network formed within the film actuated as a strong barrier to the leakage of all the water-soluble species during film immersion in water. Beside simple strategy towards improved performance of waterborne coatings, these results offer further extension of their application potential.

Application of Renewable Natural Materials for Gas and Water Shutoff Processes in Oil Wells

We propose a complex sealing compound for increasing the efficiency of shutoff operations based on natural materials processing for materials such as sand, peat, rice, and husks. We studied the influence of mechanical activation processes on the mechanical and rheological properties of the developed sealants. Through mechanochemical activation, sand dissolution in a low-concentrated alkali solution was possible, and gelling the resulting sodium silicate while reinforcing it with undissolved sand particles to obtain a sealant composition. We used this approach to produce a hybrid sealing compound based on activated rice husks with up to 20% biogenic silicon dioxide combined with mechanically activated peat: the maximum shear strain of the hybrid sealant was 27.7 ± 1.7 Pa. We produced hydrogels based on sodium silicate, polyacrylamide, and chromium acetate, reinforced with mechanically activated rice husks. We studied the sealants’ rheological and filtration properties and observed the respective viscoplastic and viscoelastic properties. An increase in the dispersion concentration from 0 to 0.5% increased the maximum strain value of undestroyed hydrogel’s structure in the range 50–91 Pa and the maximum shear strain from 104 to 128 Pa. The high residual resistance factor values of the ideal fracture model make the natural and plant-renewable raw materials very promising for repair and sealing work.

Parametric investigation of charging and discharging performances of a cascaded packed bed thermal energy storage system

The packed bed thermal energy storage (PBTES) system employing cascaded phase change material (PCM) is useful for low-grade waste heat recovery and utilization. The performance of a cascaded PBTES system is parametrically investigated in the present study. A one-dimensional concentric dispersion model is developed and validated by the experimental results. The average heat transfer rates of a cascaded PBTES system at various volumetric ratios of PCM capsules are numerically investigated, and the cascaded PBTES system of a volumetric ratio of hydroquinone: adipic acid: erythritol = 3:6:1 is found to be the best configuration in the cyclic charging and discharging processes. Furthermore, the comparison of the thermal behaviors of the cascaded and non-cascaded PBTES systems shows that the PCMs in each layer of a cascaded PBTES system complete the phase change at nearly the same time, leading to a larger heat transfer rate compared to the non-cascaded one. The average heat transfer rate of a cascaded PBTES system with the volumetric ratio of 3:6:1 is about 6.96 % higher than that of the non-cascaded one for the cyclic process. In addition, the results show that the average heat transfer rate of the cyclic process of the PBTES system is improved by employing the cascaded PCMs, while the enhancement ratio of average cyclic heat transfer rate is found to decrease from 10.57 % to −1.35 % as the mass flow rate increases from 20 kg·h−1 to 100 kg·h−1 and to decrease from 10.32 % to 0.91 % as the capsule diameter increases from 20 mm to 100 mm.

Tuning of Photoluminescence of Graphene Oxide Based Nanomaterials in the UV‐Visible Region: Formation of Aggregates by H‐Bonding through Water Molecules

AbstractTo investigate the interaction among the graphene oxide layers by involving surface functional groups, photoluminescence (PL) from graphene oxide (GO), and hydroxyl enriched graphene oxide (OH‐GO) in the UV‐visible region are studied. Tuning of PL is observed by varying the concentration of aqueous dispersion of OH‐GO, obtained by strong alkaline treatment on graphene oxide (GO). FTIR, Raman, XRD, and the microscopic study suggests the structural orderness of the OH‐GO compared to GO. Hydroxyl functional groups at the surface of OH‐GO facilitate the formation of aggregates through hydrogen bonds by involving solvent water molecules and the PL band in the visible region may be originated from such aggregates. With the increase in the concentration of OH‐GO in the aqueous medium, the contribution of the visible PL band is markedly increased along with the decrease in the PL band in the UV region. The time‐resolved study indicates the possibility of energy transfer from the species emitting in the UV region to the species emitting in the visible region. This energy transfer may be responsible for the marked enhancement of the visible band of the PL spectra of OH‐GO at high concentrations.

Nanodiamond-Based Optical-Fiber Quantum Probe for Magnetic Field and Biological Sensing.

Owing to the unique electronic spin properties, nitrogen-vacancy (NV) centers hosted in diamond have emerged as a powerful quantum tool for detecting various physical parameters and biological species. In this work, an optical-fiber quantum probe, configured by chemically modifying nanodiamonds on the surface of a cone fiber tip, is developed. Based on the continuous-wave optically detected magnetic resonance method and lock-in amplification technique, it is found that the sensing performance of probes can be engineered by varying the nanodiamond dispersion concentration and modification duration during the chemical modification process. Combined with a pair of magnetic flux concentrators, the magnetic field detection sensitivity has reached 0.57 nT/Hz1/2@1 Hz, a new record among the fiber magnetometers based on nanodiamonds. Taking Gd3+ as the demo, the capability of probes in paramagnetic species detection is also demonstrated experimentally. Our work provides a new approach to develop NV centers as quantum probes featuring high integration, multifunction, high sensitivity, etc.

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review.

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

Surface Treatment of Polylactic Acid Fiber by Starch Nanocrystals and Interface Modification of Polylactic Acid Fiber-Reinforced Starch Composites

The surface of polylactic acid fiber (PLAF) was treated with self - manufactured starch nanocrystals (SNCs) to improve its interfacial adhesion with the starch matrix. Determination of optimum dispersion conditions of SNCs dispersion by transmittance. The effects of direct oscillatory deposition, chemical grafting SNCs modification, and SNCs dispersion concentration on the surface treatment effect of PLAF and its interfacial bonding with starch matrix were investigated. The results showed that the SNCs were successfully introduced into the PLAF surface, moreover, the modifying effect of the chemical grafted SNCs was better than the direct oscillatory deposition, the distribution of SNCs particles was more uniform on the fiber surface, strong chemical bonding to the fiber surface, make up for the surface damage of the fibers caused by aminolysis. At the SNCs dispersion concentration of 10 g/L, the PLAF tensile strength could be maintained at 582 MPa, a large amount of starch was evenly attached to the surface after pulling out. It showed that a strong interface bond with the starch matrix, the highest IFSS value was 2.57 MPa and the increase was by about 63 %. Therefore, the introduction of SNCs for interfacial modification of PLAF is of great significance and deserves further exploration.

Areal Density Control of Liquid-Supported Carbon Nanotube Thin Films.

Carbon nanotube (CNT) films have extensive applications due to their excellent electrical, mechanical, and thermal properties. A grand challenge is controlling areal density of CNT films to accommodate various applications. Here, a method based on the Marangoni effect is used to fabricate liquid-supported CNT films with tunable areal density, scalable area, and transferability to arbitrary substrates. By adjusting the viscosity and surface tension of the base liquid media, the Marangoni flow area of surfactant-assisted single-walled CNT (SWCNT) dispersion on the surface of base media was controllable and sparse or dense SWCNT films can be easily obtained. The thickness of the films is controlled by changing the concentration of the SWCNT dispersion. These SWCNT-based transparent-conductive films have widely controllable transmittance and conductivity and exhibit great photoelectric properties (T ∼ 82.4%, Rs ∼ 407 Ω/sq).

The impacts of highways on firm size distribution: Evidence from China

AbstractThis paper examines the impact of highway construction on the size distribution of manufacturing firms using Chinese firm and highway network data. I construct instrumental variables using historical and counterfactual road approaches to identify the causal effects of highway construction. I find that highway construction can increase firm size dispersion and market concentration. Areas near highways have a higher number of firms, more outsourcing activities, and more large firms; while areas further from highways have a higher share of new entry firms.

Do Aqueous Suspensions of Smectite Clays Form a Smectic Liquid-Crystalline Phase?

Bottom-up strategies for the production of well-defined nanostructures often rely on the self-assembly of anisotropic colloidal particles (nanowires and nanosheets). These building blocks can be obtained by delamination in a solvent of low-dimensionality crystallites. To optimize particle availability, determination of the delamination mechanism and the different organization stages of anisotropic particles in dispersion is essential. We address this fundamental issue by exploiting a recently developed system of fluorohectorite smectite clay mineral that delaminates in water, leading to colloidal dispersions of single-layer, very large (≈20 μm) clay sheets at high dilution. We show that when the clay crystallites are dispersed in water, they swell to form periodic one-dimensional stacks of fluorohectorite sheets with very low volume fraction (<1%) and therefore huge (≈100 nm) periods. Using optical microscopy and synchrotron X-ray scattering, we establish that these colloidal stacks bear strong similarities, yet subtle differences, with a smectic liquid-crystalline phase. Despite the high dilution, the colloidal stacks of sheets, called colloidal accordions, are extremely robust mechanically and can persist for years. Moreover, when subjected to AC electric fields, they rotate as solid bodies, which demonstrates their outstanding internal cohesion. Furthermore, our theoretical model captures the dependence of the stacking period on the dispersion concentration and ionic strength and explains, invoking the Donnan effect, why the colloidal accordions are kinetically stable over years and impervious to shear and Brownian motion. Because our model is not system specific, we expect that similar colloidal accordions frequently appear as an intermediate state during the delamination process of two-dimensional crystals in polar solvents.