Low Particle Concentrations Research Articles

LCZ method is more effective than traditional LUCC method in interpreting the relationship between urban landscape and atmospheric particles

Landscape classification methods significantly impact the exploration of the mechanism of the relationship between landscapes and atmospheric particulate matter. This study compared the local climate zones (LCZs) and traditional land use/cover change (LUCC) landscape classification methods in explaining spatial differences in concentrations of atmospheric particulate matter (PM2.5 and PM10) and explored the mechanisms involved in how landscape elements affect atmospheric particulate matter. This was done by establishing a PM2.5 and PM10 land use regression (LUR) model of LCZ and LUCC landscapes under low, typical, and high particle concentration gradients in urban and suburban areas. The results show that under an LCZ classification system, the number of patches in the urban area of Shanghai was 548 times higher than that of a LUCC system. Moreover, LCZs were successfully established for LUR models in 12 scenarios, while only five models were established for LUCC, all of which were suburban models. The R2 of the LUR model based on the LCZ landscape and atmospheric particulate matter was mostly higher than that of the LUCC. For unnatural landscapes, the LUCC demonstrated that an urbanized environment positively affects the concentration of atmospheric particles. However, the LCZ analysis found that areas with high-density buildings have a positive effect on atmospheric particles, while most areas with low-density buildings significantly reduced the number of atmospheric particles present. Generally, compared with the traditional LUCC landscape classification method, LCZ integrates Shanghai's physical structure and classifies the urban landscape more accurately, which is closely related to the urban atmospheric particulate matter, especially in the urban area. Because the low-density building area has the same effect on the particulate matter as the natural landscape, the use of low-density buildings is recommended when planning new towns.

Well-posedness and ill-posedness of single-phase models for suspensions

Classical theories for suspensions have been formulated by starting from the Navier–Stokes equations describing pure liquid flow and then introducing additional dependencies to account for the presence of suspended particles. These models are often accurate for low particle concentrations but have lacked a convincing description of the frictional interactions of particles, which are important at larger solid volume fractions. The $\mu (J), \varPhi (J)$ rheology, which draws a direct analogy between suspension flow and dry granular flow, is a recent theory that addresses this issue, but is shown here to be dynamically ill-posed for large solid volume fractions. An alternative well-posed theory is introduced that includes additional dependence on the particle-phase dilation and compression. The new theory, denoted vCIDR, is tested numerically to show grid convergence for problems in which the $\mu (J), \varPhi (J)$ rheology instead suffers from catastrophic blow-up. A further well-posed extension provides a framework for handling the transition between viscous and inertial flows.

Particle field deconvolution multiplicative algebraic reconstruction technique for tomographic particle image velocimetry reconstruction

Precision tomographic reconstruction is critical for obtaining high-accuracy velocity measurements in tomographic particle image velocimetry. Traditional tomographic reconstruction methods, such as the multiplicative algebraic reconstruction technique (MART), can only be applied at low particle concentrations, limiting the spatial resolution of velocity measurements. In addition, the actual shape of the particles is not reconstructed well due to the limited views. In this study, we propose a novel method named particle field deconvolution MART (Deconv-MART) to repair the shape of actual particles while suppressing ghost particles reconstructed by MART iterations. This method first uses the Gaussian particle shape prior to estimate the convolution kernel obtained by MART reconstruction. Then, the estimated kernel is utilized to deconvolute the particle field and suppress ghost particles based on the prior information of the lower intensity of ghost particles as well as the sparsity of the particle field. Reconstruction fields are estimated with numerical and real experiments, and the results are compared with the results of advanced reconstruction methods. Comparisons of reconstruction demonstrate that the proposed method is effective at suppressing ghost particles and restoring the shape of actual particles. Comparisons of velocity measurements reveal that Deconv-MART has good performance and high measurement accuracy.

Hydrophilic surface-modified 3D printed flexible scaffolds with high ceramic particle concentrations for immunopolarization-regulation and bone regeneration.

Bioceramic scaffolds used in bone tissue engineering suffer from a low concentration of ceramic particles (<50 wt%), because the high concentration of ceramic particles increases the brittleness of the composite. 3D printed flexible PCL/HA scaffolds with high ceramic particle concentrations (84 wt%) were successfully fabricated in this study. However, the hydrophobicity of PCL weakens the composite scaffold hydrophilicity, which may limit the osteogenic ability to some extent. Thus, as a less time-consuming, less labour intensive, and more cost-effective treatment method, alkali treatment (AT) was employed to modify the surface hydrophilicity of the PCL/HA scaffold, and its regulation of immune responses and bone regeneration were investigated in vivo and in vitro. Initially, several concentrations of NaOH (0.5, 1, 1.5, 2, 2.5, and 5 mol L-1) were employed in tests to determine the appropriate concentration for AT. Based on the comprehensive consideration of the results of mechanical experiments and hydrophilicity, 2 mol L-1 and 2.5 mol L-1 of NaOH were selected for further investigation in this study. The PCL/HA-AT-2 scaffold dramatically reduced foreign body reactions as compared to the PCL/HA and PCL/HA-AT-2.5 scaffolds, promoted macrophage polarization towards the M2 phenotype and enhanced new bone formation. The Wnt/β-catenin pathway might participate in the signal transduction underlying hydrophilic surface-modified 3D printed scaffold-regulated osteogenesis, according to the results of immunohistochemical staining. In conclusion, hydrophilic surface-modified 3D printed flexible scaffolds with high ceramic particle concentrations can regulate the immune reactions and macrophage polarization to promote bone regeneration, and the PCL/HA-AT-2 scaffold is a potential candidate for bone tissue repair.

Experimental research on flammability characteristics and ignition conditions of hybrid mixture emissions venting from a large format thermal failure lithium-ion battery

When the concentration of gas is below its lower flammable limit and the content of the particles is below its minimum explosible concentration, it can be explosible. Thermal abuse tests for 50 Ah lithium-ion batteries were conducted under an inert atmosphere. The battery failure venting emissions were collected and their composition was identified previously. It still needs further research for the flammability characteristics and ignition conditions for hybrid mixture emissions venting from a large format lithium-ion battery thermal failure. In this study, the likelihood, severity, and kinetics of the batteries' hybrid mixture emissions flammability have been researched. To analyze battery emission flammability characteristics, five indexes have been investigated; they are ignition temperature (Tig), ignition time (τig), maximum explosion pressure (Pmax), pressure rise maximum rate ((dP/dτ)max), and size-normalized maximum rate pressure rise (KSt). Based on quantitative analysis for the hybrid mixture flammability characteristics, it indicates that particle size and gas content can impact hybrid mixture emission flammability characteristics. As for the mixture with finer particles, the optimum combustion condition of the particle and gas concentration pairs were 0.3 and 0.7. The ignition temperature for the optimum combustion conditions was 495 °C. The pressure rising velocity was 23 Mpa/s during ignition. High solvent content and low particle concentration are the conditions for optimum combustion. This indicates that the gas admixture solvent plays a major role in the combustion kinetics of the mixture emission. This research offers a fundamental perspective and provides preventive and protective thermal safety designs that are more suitable for large format commercial battery thermal systems.

Evaporation Caused Invaginations of Acoustically Levitated Colloidal Droplets.

Controlled buckling of colloidal droplets via acoustic levitation plays an important role in pharmaceutical, coating, and material self-assembly. In this study, the evaporation process of PTFE colloidal droplets with two particle concentrations (60 wt% and 20 wt%) was investigated under acoustic levitation. We report the occurrence of surface invagination caused by evaporation. For the high particle concentration droplet, the upper surface was invaginated, eventually forming a bowl-shaped structure. While for the low particle concentration droplet, both the upper and lower surfaces of the droplet were invaginated, resulting in a doughnut-like structure. For the acoustically levitated oblate spherical droplet, the dispersant loss at the equatorial area of the droplet is greater than that at the two poles. Therefore, the thickness of the solid shell on the surface of the droplet was not uniform, resulting in invagination at the weaker pole area. Moreover, once the droplet surface was buckling, the hollow cavity on the droplet surface would absorb the sound energy and results in strong positive acoustic radiation pressure at bottom of the invagination, thus further prompting the invagination process.

INFLUENCE OF CLADOSPORIUM CLADOSPORIOIDES METABOLITES ON VIRAL INFECTION DYNAMICS IN POTATO PLANTS UNDER CONDITION OF NATURAL AND ARTIFICIAL PHYTOVIRAL INFECTION

Objective. Study the influence of Cladosporium cladosporioides metabolites on viral infection dynamics in potato plants under conditions of artificial and natural infection. Methods. Laboratory (virological, immunological, electron microscopic), field, statistical. Results. The influence of microbial metabolites on the development of viral infection in potato plants was studied in 2021 and 2022 under the conditions of a small field experiment. In 2021, under the conditions of protection against re-infection in the variants artificially infected with potato virus X (PVX), visual and immunological methods did not reveal any plants with symptoms of viral damage, the electron microscopic examination showed a low concentration of virus particles in plants, which probably caused due to abnormally high temperature during the vegetation of micro-plants. Treatment of plants with C. cladosporioides metabolites did not significantly affect the accumulation of PVX. In the experiments of 2022, tubers from healthy and artificially infected microplants from variants with and without treatment of plants with C. cladosporioides metabolites were used. The analysis of the viral infection dynamics under the conditions of natural infection with phytopathogenic viruses and previous artificial infection with PVX showed that C. cladosporioides metabolites affect the development of viral infection. In most variants using microbial metabolites, the rate of visual manifestation of the viral disease was 3 % to 5 % lower compared to the control. The frequency of detection of viruses by the immunological method was higher in the control variant and was equal to 40 %, the lowest number of detected infected plants was reported in the variant when the plants were treated with C. cladosporioides metabolites for two consecutive years and was equal to 22.5 %. The greatest decrease in the viral protein content, which indicates a decrease in virus reproduction, was reported when C. cladosporioides metabolites were applied in the first and second years in the variants artificially infected with PVX in 2021 — the difference to the control was 38 %. We believe that the influence of C. cladosporioides metabolites on the viral infection dynamics in potato plants is caused by exohormonal substances included in their composition. Conclusion. The results of two-year studies show that C. cladosporioides metabolites influence the viral infection dynamics. A decrease in the rate of visual manifestations of viral disease is registered. The lowest number of infected plants was found in the variant when the plants were treated with C. cladosporioides metabolites for consecutive two years. Also, the action of microbial metabolites reduces the concentra tion of viral protein in potato plants. Such a reaction of the “plant-virus” system indicates the inhibitory activity of C. cladosporioides metabolites against viruses.

Numerical investigation of the radiative properties of a fully resolved particle cloud

In this study, the interaction of thermal radiation with dense solid fuel particle clouds is investigated numerically. To determine absorption and scattering properties of a particle cloud, generally, the absorption and scattering efficiencies of single particles are calculated by Mie theory, and subsequently, these parameters are linearly scaled by the particle number density to obtain representative coefficients for the particle cloud. Theoretically, this approach is only valid for clouds with perfectly uniformly distributed particles. However, real particle clouds are characterized by non-uniform particle distributions within the cloud. This results in the radiation being able to penetrate areas with low particle concentration almost unhindered, while areas with high particle concentrations are subject to multiple particle-radiation interactions.To evaluate the impact of non-uniform particle distributions on the radiative heat transfer, generic particle clouds with random distributions are generated. The cell size of the numerical grid is chosen in such a way that each individual particle is resolved, while each cell either represents particle or gas properties. The radiative heat transfer through the particle cloud is solved numerically via the Monte-Carlo ray-tracing method. The particle-resolved approach and the linear scaled approach are compared based on the intensity loss as a function of penetrating depth.The absorption behavior of a particle cloud modeled by a non-uniform particle distribution indicates a value up to 30% lower than the one of a perfectly uniform particle distribution. The investigations have further shown that it is possible to consider the effects of the particle-resolved approach by a modified weighting factor, which takes into account the particle size and absorption efficiency in addition to the particle number density. This allows numerical calculations without resolution of individual particles (low numerical effort) with similar accuracy compared to the particle-resolved simulations. Since dependent scattering effects are not modeled, the modified weighting factor is only applicable for particle clouds with a particle volume fraction below P<0.01.

Diagnostic performance of attenuated total reflection Fourier-transform infrared spectroscopy for detecting COVID-19 from routine nasopharyngeal swab samples

Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy coupled with machine learning-based partial least squares discriminant analysis (PLS-DA) was applied to study if severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could be detected from nasopharyngeal swab samples originally collected for polymerase chain reaction (PCR) analysis. Our retrospective study included 558 positive and 558 negative samples collected from Northern Finland. Overall, we found moderate diagnostic performance for ATR-FTIR when PCR analysis was used as the gold standard: the average area under the receiver operating characteristics curve (AUROC) was 0.67–0.68 (min. 0.65, max. 0.69) with 20, 10 and 5 k-fold cross validations. Mean accuracy, sensitivity and specificity was 0.62–0.63 (min. 0.60, max. 0.65), 0.61 (min. 0.58, max. 0.65) and 0.64 (min. 0.59, max. 0.67) with 20, 10 and 5 k-fold cross validations. As a conclusion, our study with relatively large sample set clearly indicate that measured ATR-FTIR spectrum contains specific information for SARS-CoV-2 infection (P < 0.001 for AUROC in label permutation test). However, the diagnostic performance of ATR-FTIR remained only moderate, potentially due to low concentration of viral particles in the transport medium. Further studies are needed before ATR-FTIR can be recommended for fast screening of SARS-CoV-2 from nasopharyngeal swab samples.

Impacts of viaduct and geometry configurations on the distribution of traffic-related particulate matter in urban street canyon

Viaduct is a ubiquitous transportation infrastructure in the congested megacities worldwide to improve the accessibility and capacity of urban transportation network. However, there is a lack of understanding of the impacts of the interplay between viaduct-ground emissions and viaduct-canyon configurations on the particle distribution in urban street canyon. To fill the research gap, we conducted vertical measurements of particle number concentrations (PNCs) at different heights of “street canyon along a viaduct” to reveal effect of viaduct on the vertical distribution of PNCs in street canyon. Observation results indicated that the vertical profiles of PNCs exhibited bimodal distribution patterns, which were more significant for coarse particles than fine particles. The one peak appeared at ground level and the other at the viaduct height, indicating the impacts of “double” emission sources (i.e., the emissions on the ground and viaduct) and the hindrance of viaduct to particle diffusion. We further modelled the role of viaduct in street canyon through Computational Fluid Dynamics (CFD) simulations to reveal the vertical distribution of particles under different viaduct-canyon configurations and discern the contributions of viaduct and ground emissions to the particle distribution. Simulation results showed that viaduct changed airflow field and turbulence structure and elevated particle concentrations in street canyon while the optimized viaduct-canyon configurations including higher viaduct height (12 > 10 > 8 m), smaller aspect ratio (0.5 > 0.67 > 1), and shorter centerline distance (0 > 1 > 2 m) between canyon and viaduct could bring better dispersion conditions and lower particle concentrations. Additionally, ground emissions contributed more to the vertical distribution of particles on the leeward side of street canyon than viaduct emissions while the windward side displayed the opposite characteristics to the leeward side. These findings revealed the general patterns of particle diffusion in viaduct-canyon configurations and provided implications into viaduct design and traffic management to alleviate local particulate pollution.

Effective Cooling System for Solar Photovoltaic Cells Using NEPCM Impingement Jets

Attention to photovoltaic (PV) cells to convert solar irradiation into electricity is significantly growing for domestic usage and large-scale projects such as solar farms. However, PV efficiency decreases on hot days. This paper proposes an effective cooling technique consisting of a 2% nano encapsulated phase change material (NEPCM) slurry and impinging jets (IJs) in a PV system. The impact of five influencing parameters on PV efficiency is studied using a multi-phase volume of fluid (VOF) model encompassing the effects of solar irradiation, latent heat, mass flow rate, number of nozzles, and jet-to-surface distance. The maximum efficiency of 15.82% is achieved under irradiation of 600 W/m2. The latent heat shows a slight improvement at the low particle concentration. Increasing the mass flow rate to 0.12 kg/s enhances the PV output power by 17.32%. While the PV performance is shown to be improved over the increment of the number of nozzles, the jet-to-surface spacing of 5.1 mm records a remarkable PV surface temperature reduction to 33.8 °C, which is the ideal operating temperature for the PV panel.

Effect of the Tubing Material Used in Peristaltic Pumping in Tangential Flow Filtration Processes of Biopharmaceutics on Particle Formation and Flux

Tangential flow filtration (TFF) is a central step in manufacturing of biopharmaceutics. Membrane clogging leads to decreased permeate flux, longer process time and potentially complete failure of the process. The effect of peristaltic pumping with tubings made of three different materials on protein particle formation during TFF was monitored via micro flow imaging, turbidity and photo documentation. At low protein concentrations, pumping with a membrane pump resulted in a stable flux with low protein particle concentration. Using a peristaltic pump led to markedly higher protein particle formation dependent on tubing type. With increasing protein particle formation propensity of the tubing, the permeate flux rate became lower and the process took longer. The protein particles formed in the pump were captured in the cassette and accumulated on the membrane leading to blocking. Using tubing with a hydrophilic copolymer modification counteracted membrane clogging and flux decrease by reducing protein particle formation. In ultrafiltration mode the permeate flux decrease was governed by the viscosity increase rather than by the protein aggregation; but using modified tubing is still beneficial due to a lower particle burden of the product. In summary, using tubing material for peristaltic pumping in TFF processes which leads a less protein particle formation, especially tubing material with hydrophilic modification, is highly beneficial for membrane flux and particle burden of the product.

Formation, structure and stability of high internal phase Pickering emulsions stabilized by BSPI-C3G covalent complexes.

Food-grade high internal phase Pickering emulsions (HIPPEs) are stabilized by protein-based particles, which have attracted extensive attention due to their good gel-like structure. The black soybean isolate protein/cyanidin-3-O-glucoside (BSPI-C3G) covalent particles were used as a particulate emulsifier to form stable HIPPEs with oil phase fractions (74% v/v) and low particle concentrations (0.5%-3% w/v) The particle size distribution and microstructure demonstrated that the BSPI-C3G covalent particles acted as an interfacial layer and surrounded the oil droplets. As the concentration of BSPI-C3G particles increased from 0.5% to 3%, the droplet size, elasticity, antioxidant capacity of the heated or stored HIPPEs more stable. So, the HIPPEs had the best stability with the BSPI-C3G particle at 3% (w/v) concentration. These findings may extend the application of BSPI and C3G in foods and provide the guidelines for the rational design of food-grade HIPPEs stabilized by protein/anthocyanin complexes.

Role of particle-laden interfaces in shear-induced deformation of colloidal droplets

In this study, basing on the level-set and point-particle methods, we have developed a numerical methodology for simulating the dynamics of colloidal droplets under flow conditions in which the particle–particle, particle–interface and particle–fluid interactions are all taken into account efficiently. By using this methodology, we have determined the essential role of particle-laden interfaces in the deformation of colloidal droplets in simple shear flow with relatively low particle concentrations. Generally, adsorbed particles strongly enhance the deformability of the whole droplet, which is principally attributed to the particle-induced reduction of the effective surface tension. Systematic simulations are performed to reveal the detailed roles of interparticle interactions and particle surface coverage in the deformation of particle-covered droplets. Most importantly, we find the promotion effect of adsorbed particles on the droplet deformation cannot be completely included via the effective capillary number characterizing the particle-induced overall reduction of the effective surface tension, which is particularly obvious at high particle coverage. We propose two potential reasons for this surprising phenomenon, i.e. the convection-induced non-uniform distribution of adsorbed particles over the droplet surface and the particle-induced reduction of the droplet surface mobility, which have not been discussed yet in previous numerical and experimental studies of particle-covered droplets in shear flow.

Influence of particle wettability on foam formation in honey

The rising level of obesity is often attributed to high sugar and/or fat consumption. Therefore, the food industry is constantly searching for ways to reduce or eliminate sugar or fat in food products. Therefore, honey foam, which contains little sugar and no fat, can be used as cake, cracker or bread spread instead of butter or margarine which contains a substantial amount of fat or jam that contains a substantial amount of sugar. Small solid particles (nanometers to micrometers) of suitable wettability are now considered outstanding foam-stabilizing agents. However, while the degree of particle wettability necessary to obtain very stable aqueous and nonaqueous foams is well-known, that needed to obtain very stable honey foam is unknown. In this study, the influence of the degree of wettability of fumed silica particles, indicated by their % SiOH (14–100), was investigated in honey in relation to foam formation and foam stability. The honephilic particles (61%–100% SiOH) formed particle dispersion in honey, while foams were obtained with the honephobic particles (14%–50% SiOH). The thread-off between particle dispersion and foam formation occurs at 50% SiOH, meaning foam formation in honey is possible when the particles are at least 50% honephobic. At relatively low particle concentration <1 wt.%, foam volume decreases with increasing honephobicity, but increases with honephobicity at relatively high concentration >1 wt.%. Also, as particle concentration increases, the shape of the air bubbles in the foam changes from spherical to non-spherical. After a little drainage, the foams remain stable to drainage and did not coalesce substantially for more than six months. These findings will guide the formulation of edible Pickering honey foams.

Treatment of Municipal Wastewater by Hollow Fiber Dynamic Membrane Bioreactors

AbstractIn this study, an aerobic membrane bioreactor (MBR) with a polyester fabric hollow fiber filter is used for municipal wastewater treatment. This polyester fabric filter is used as support material for dynamic membrane formation in the MBR. High treatment performance is obtained in the permeate achieving over 93% of chemical oxygen demand removal efficiency and low particulate material concentration (&lt;10 mg L−1). The system is operated for 58 d without any clogging. The average transmembrane value is found as around 598 mbar after the system reaches stable conditions. Morphological analyses including confocal laser scanning microscopy, environmental scanning electron microscopy, energy‐dispersive X‐ray, and Fourier transform infrared spectroscopy are performed to obtain a detailed understanding of the cake layer formation. The use of hollow fiber dynamic membranes can provide compact membrane volume with high surface area, thus, the volume of the reactor can be further decreased.

Finding the tiny plastic needle in the haystack: how field flow fractionation can help to analyze nanoplastics in food.

While the exact health risks associated with nanoplastics are currently the focus of intense research, there is no doubt that humans are exposed to nanoplastics and that food could be a major source of exposure. Nanoplastics are released from plastic materials and articles used during food production, processing, storage, preparation, and serving. They are also likely to enter the food chain via contaminated water, air, and soil. However, very limited exposure data for risk assessment exists so far due to the lack of suitable analytical methods. Nanoplastic detection in food poses a great analytical challenge due to the complexity of plastics and food matrices as well as the small size and expectedly low concentration of the plastic particles. Multidetector field flow fractionation has emerged as a valuable analytical technique for nanoparticle separation over the last decades, and the first studies using the technique for analyzing nanoplastics in complex matrices are emerging. In combination with online detectors and offline analysis, multidetector field flow fractionation is a powerful platform for advanced characterization of nanoplastics in food by reducing sample complexity, which otherwise hampers the full potential of most analytical techniques. The focus of this article is to present the current state of the art of multidetector field flow fractionation for nanoplastic analysis and to discuss future trends and needs aiming at the analysis of nanoplastics in food.

Long-Term Exposure to Polystyrene Nanoplastics Impairs the Liver Health of Medaka

Nanoplastic (NP) has become a global environmental concern due to its potentially wide distribution and unknown impacts on organisms. Many laboratory studies have reported the short-term toxicity of NPs but their long-term effects are unclear. Here, the chronic hepatoxic effects of NPs (diameter 100 nm; 0, 10, and 104 items/L) in medaka (Oryzias latipes) were evaluated after three-month exposure by investigating the alterations in enzymatic biomarkers (digestion, oxidative status, and immunity) and histopathology in the liver. The trypsin and chymotrypsin activities of digestive enzymes were induced at a low concentration of NPs (10 items/L) but inhibited at high concentration (104 items/L); only the amylase activity was significantly decreased in all NP-treated medaka. Oxidative stress was also induced by NP exposure, which was indicated by the responsive superoxide dismutase and catalase. Lysozyme was significantly reduced after exposure to a high concentration of NPs, while alkaline phosphatase was significantly induced at a low concentration. Exposure to NPs also caused liver damage (e.g., congestion and dilated sinusoids). Taken together, our findings show that chronic exposure to NPs at low particle concentrations can impair the liver health of medaka by affecting liver enzymatic functions and causing histological damage. This implies potentially long-term threats of NPs to aquatic organisms, which call for more long-term aquatic toxicological studies on various species using low environmental concentrations.

Real-time tracking of colloidal stability based on collision behaviors probed by surface-enhanced Raman spectroscopy

HypothesisThe dynamic behaviors of colloidal particles have already been considered as one of the key issues in their practical application, such as aggregation and dispersion. However, it is still remained significant challenge in developing the real time techniques to capture their dynamic tracks. The nano/subnanometer scale gap generated during the colloidal collisions served as the critical location for amplifying the Raman signal, so called as gap (“hot spots”) based surface enhanced Raman spectroscopy (SERS). The alternating reversible “spike” of SERS intensity and irreversible step in baseline intensity are contributed to the preferred stability and the aggregation of colloid respectively. ExperimentsA facile approach is developed to track colloidal stability in real-time based on collisions and SERS. The effects of particle concentration, the dispersion medium, and solution pH on colloidal stability are systematically investigated, and the SERS intensity of a simulated single-like “hot spot” was calculated by combining a SEM position with SERS mapping technology to estimate the intensity of single-particle collision. FindingsThe colloidal particles exhibited higher stability in the solution with lower particle concentration, higher viscosity and neutral medium. The SERS intensity of single-particle collision was estimated to be about 2.06 × 10-7 counts, and the average number of collisions for the 0.13 mmol/dm3 SiO2@Ag solution was about 1.11 × 108 times/spike in the “spikes” with SERS intensity of 23.0 cps. It is believed that the SERS based strategy would be developed as a promising tool for obtaining the deeper insight into the nature of collisions in the colloidal science.

A novel Pickering emulsion stabilized solely by hydrophobic agar microgels

A novel agar-based Pickering emulsion stabilizer was developed through the hydrophobic modification and microgelation of agar. After hexanoylation, the three-phase contact angle of hexanoylated agar (HAG) particles was adjusted from approximately 60° to 96° closing to neutral wettability. After microgelation, the particle size of the modified agar microgel was approximately 2 μm and Zeta potential reached −23.63 mV. Confocal laser microscopy and cryogenic scanning electron microscopy showed that HAG microgels formed a gel network or embedded on the surface of oil droplets, thus providing a dense barrier for oil droplets to coalesce and Ostwald ripening. The oil volume fraction and particle concentration had a significant effect on the droplet size and rheological properties of the Pickering emulsion. Pickering emulsion gels with long-term storage stability was prepared at low particle concentrations (0.7 wt%) and lower oil fractions (φ = 0.3– 0.5), which might become a new effective delivery system for bioactive substances.