Water Agglomerates Research Articles

Dual-function starch aerogels: Nutraceutical carriers for iron and folic acid delivery

Iron and folic acid are especially important in pregnancy, where supplementation is often the only path to prevent anemia. Despite the available commercial solutions, the challenges of enhancing nutrient absorption and reducing side effects foster the search for novel approaches. In this work, freeze-dried starch aerogels were developed to act as nutraceutical carriers for co-delivery and tested under simulated digestion conditions. Iron and folic acid were loaded into starch gels, both separately and mixed. Iron presented a faster release than folic acid in intestinal conditions, reaching 75–80 % after 10 and 90 min, respectively. Molecular modeling suggests that folic acid interacts with amylose agglomerates in water by hydrogen bonds, probably delaying its release. Co-delivery of these nutraceuticals seems to not affect the release behavior. The Korsmeyer-Peppas kinetic model fits well to all release profiles. The proposed starch aerogel is a promising solution and further development can increase its competitiveness against conventional supplements.

Effect of Various Concentrations of Sodium Hydroxide/Hot Alkali Treatment on the Physical Properties of Ramie Fibres

The preparation stages that precede the final treatment with a chemical treatment like alkali determine the physical characteristics of ramie fibres. It modified the hydroxyl group which is responsible for the hydrogen bonding of the fibres. This work examined the pre-treatment of ramie fibres with acetone followed by alkali or hot alkali with various concentrations. The immersion of ramie fibres in certain percentages of sodium hydroxide solution resulted in a good performance of their physical characteristics. The ramie fibres treated with 10% NaOH exhibit the best dispersion stability and low agglomeration or precipitation in water with an amount of 14%. When alkali is applied to ramie fibres, the hydrophilic group on their surface grows, potentially improving the fibre's capacity to absorb water. However, when the concentration is increased to 15%, the dispersion stability of sodium hydroxide performs less well. The fibres' ability to absorb water was diminished and they became brittle due to a high alkali content. In addition to the aforementioned characteristics, the properties of precipitation and water absorption were unaffected by the hot alkaline process for all samples. The hot alkali process (80°C) was not able to generate a further breakdown of hydrogen bonds of the fibres.

Linking the ionomer film morphology and nanoscale oxygen transport properties in fuel cells

Transport processes are crucial for the performance of electrochemical energy conversion devices and attract wide attentions. This work focuses on the critical oxygen transport process in the ionomer electrolyte film on a Pt electrode, which highly limits the performance of low Pt-loading fuel cells. Reduction of oxygen transport resistance may be achieved by optimizing the ionomer film morphology. Therefore, the relationship between ionomer film morphology and oxygen transport characteristics is explored by altering ionomer side chain lengths in this work. The results show that the swollen structure with larger water agglomerates in the ionomer film with shorter ionomer side chains is detrimental to the formation of oxygen transport paths. However, the multilamellar structure with an alternating alignment of water agglomerates and PFSA ionomer agglomerates in the ionomer film with longer ionomer side chains has a larger water-PFSA interface, which provides more oxygen transport paths and thus reduces the oxygen transport resistance. This work inspires the novel design concept of the ionomer electrolyte film with low local oxygen transport resistance, i.e., enlarging the water-PFSA interface parallel to the oxygen transport direction via altering the ionomer material properties, which is valuable for the development of low Pt-loading fuel cells.

Construction of defective ZnIn2S4 and immobilized TiO2 heterostructures: Synergistic regulation of ZnIn2S4/TiO2/MS-SiO2 composite photocatalyst performance

Defect engineering and heterojunction are the two dominant methods to improve the efficiency of semiconductor photocatalysis. Loading can also improve the performance of photocatalysts and solve the problems of photocatalyst agglomeration and difficult recovery in water. In this paper, a ternary ZnIn2S4/TiO2/MS-SiO2 composite photocatalyst (EG-ZIS/TS) was constructed by sequentially loading nano-TiO2 and defective state ZnIn2S4 (EG-ZIS) on industrial by-product SiO2 microspheres (MS-SiO2). Among them, EG-ZIS was prepared with ethylene glycol as a solvent. Compared with EG-ZIS/T (unloaded MS-SiO2) and ZIS/TS (non-defected state ZnIn2S4), the degradation performance of methyl orange (MO) solution and the reduction performance of hexavalent chromium under simulated daylight irradiation were substantially improved. As a result, Zn defects enhanced the photocatalytic performance of ZnIn2S4 and the heterojunction between ZnIn2S4 and TiO2, and this enhancement was achieved by adjusting the work function of the system and promoting interface electronic transmission. The loading of MS-SiO2 further produced a synergistic effect of enhancing the heterojunction photocatalytic efficiency by improving the dispersion and immobilization of TiO2 and EG-ZIS. The effect of ethylene glycol on the curvature and surface Zn defectivity of ZnIn2S4 nanosheets was also investigated in this study. This study provides an innovative approach to improve the oxidation and reduction performance of photocatalysts by combining semiconductor defect, heterojunction, and loading on the carrier surface and finds that the loading of photocatalysts on the SiO2 carrier surface has an enhancement effect on the performance of the formed heterojunction. This thesis is useful and informative for related research.

Impact of H2O on CO2 adsorption and co-adsorption: Mechanism and high-performance adsorbents for efficient H2O-CO2 capture

Physical adsorbents used for CO2 capture from air directly and wet CO2 flue gas have limited effectiveness due to competitive adsorption of H2O and CO2. Therefore, it is crucial to understand the impact of H2O on CO2 adsorption and investigate the co-adsorption mechanism in order to enhance the screening, design, and optimization of carbon capture systems. Herein, heat treatments are performed on commercial NaX zeolites to modify the composition of the O-T-O (T = Al, Si) framework. Our systematic investigation based on thermogravimetric analysis/differential scanning calorimetry (TG-DSC), infrared spectroscopy (IR), solid-state nuclear magnetic resonance (SSNMR), and density-functional theory (DFT) calculation, the connection between the structure of NaX zeolite and H2O and CO2 adsorption/desorption is established. The heat-induced changes in the O-T-O (T = Al, Si) framework produce movements of the loaded Na+ ions. Hydrogen bonds formed by agglomerated adsorbed H2O constitute the primary source of desorption heat, which adversely affects CO2 mass transfer and adsorption. Our findings illustrate that modifying the distribution of Na+ ions in the O-T-O (T = Al, Si) framework can reduce the CO2 adsorption energy and prevent the formation of water agglomerates. Our findings provide insights into the design of efficient and high-capacity adsorbents for CO2 capture that can be operated in the presence of H2O.

Effect of Silica Nanoparticles to Span 80 and Cocamidopropyl Dimethylamine in Methane Hydrate Formation and Agglomeration in Water–Oil System

Effect of Silica Nanoparticles to Span 80 and Cocamidopropyl Dimethylamine in Methane Hydrate Formation and Agglomeration in Water–Oil System

Effect of Mixing Time on Properties of Whole Wheat Flour-Based Cookie Doughs and Cookies.

This study investigated if whole wheat flour-based cookie dough's physical properties were affected by mixing time (1 to 10 min). The cookie dough quality was assessed using texture (spreadability and stress relaxation), moisture content, and impedance analysis. The distributed components were better organized in dough mixed for 3 min when compared with the other times. The segmentation analysis of the dough micrographs suggested that higher mixing time resulted in the formation of water agglomeration. The infrared spectrum of the samples was analyzed based on the water populations, amide I region, and starch crystallinity. The analysis of the amide I region (1700-1600 cm-1) suggested that β-turns and β-sheets were the dominating protein secondary structures in the dough matrix. Conversely, most samples' secondary structures (α-helices and random coil) were negligible or absent. MT3 dough exhibited the lowest impedance in the impedance tests. Test baking of the cookies from doughs mixed at different times was performed. There was no discernible change in appearance due to the change in the mixing time. Surface cracking was noticeable on all cookies, a trait often associated with cookies made with wheat flour that contributed to the impression of an uneven surface. There was not much variation in cookie size attributes. Cookies ranged in moisture content from 11 to 13.5%. MT5 (mixing time of 5 min) cookies demonstrated the strongest hydrogen bonding. Overall, it was observed that the cookies hardened as mixing time rose. The texture attributes of the MT5 cookies were more reproducible than the other cookie samples. In summary, it can be concluded that the whole wheat flour cookies prepared with a creaming time and mixing time of 5 min each resulted in good quality cookies. Therefore, this study evaluated the effect of mixing time on the physical and structural properties of the dough and, eventually, its impact on the baked product.

Carboxylated superparamagnetic Fe3O4 nanoparticles modified with 3-amino propanol and their application in magnetic resonance tumor imaging

BackgroundUltrasmall superparamagnetic iron oxide (USPIO) nanoparticles are of potential magnetic resonance imaging (MRI) contrast agents for tumor diagnosis. However, ultrasmall particle size or negative surface charge lead to relative short half-life which limit the utilization of USPIO for in vivo MRI contrast agents.MethodsSuperparamagnetic Fe3O4 nanoparticles coated with polyacrylic acid (PAA)were synthetized, and modified by 3-amino propanol and 3-diethyl amino propyl amine. The characteristics of superparamagnetic Fe3O4 nanoparticles were investigated through transmission electron microscopy, X-ray diffraction analysis, Zata potential analysis, thermogravimetric analysis, and relaxation properties analysis. Magnetic resonance imaging animal experiment was performed.ResultsThe synthetized nanoparticles were irregular spherical, with small particle size, few agglomeration, and good dispersion in water. After modification, the potential fluctuation of nanoparticles was small, and the isoelectric point of nanoparticles changed to high pH. After 3-amino propanol modification, the weight loss of the curve from 820 to 940 °C was attributed to the decomposition of 3-amino propanol molecules on the surface. The T1 relaxation rate of nanoparticles changed little before and after modification, which proved that the modification didn’t change the relaxation time. Brighter vascular images were observed after 3-amino propanol modification through measurement of magnetic resonance tumor imaging.ConclusionThese data indicated the Fe3O4 nanoparticles modified by 3-amino propanol should be a better contrast agent in the field of magnetic resonance tumor imaging.

Novel C60 Fullerenol-Gentamicin Conjugate-Physicochemical Characterization and Evaluation of Antibacterial and Cytotoxic Properties.

This study aimed to develop, characterize, and evaluate antibacterial and cytotoxic properties of novel fullerene derivative composed of C60 fullerenol and standard aminoglycoside antibiotic–gentamicin (C60 fullerenol-gentamicin conjugate). The successful introduction of gentamicin to fullerenol was confirmed by X-ray photoelectron spectroscopy which together with thermogravimetric and spectroscopic analysis revealing the formula of the composition as C60(OH)12(GLYMO)11(Gentamicin)0.8. The dynamic light scattering (DLS) revealed that conjugate possessed ability to form agglomerates in water (size around 115 nm), while Zeta potential measurements demonstrated that such agglomerates possessed neutral character. In vitro biological assays indicated that obtained C60 fullerenol-gentamicin conjugate possessed the same antibacterial activity as standard gentamicin against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Escherichia coli, which proves that combination of fullerenol with gentamicin does not cause the loss of antibacterial activity of antibiotic. Moreover, cytotoxicity assessment demonstrated that obtained fullerenol-gentamicin derivative did not decrease viability of normal human fibroblasts (model eukaryotic cells) compared to control fibroblasts. Thus, taking into account all of the results, it can be stated that this research presents effective method to fabricate C60 fullerenol-gentamicin conjugate and proves that such derivative possesses desired antibacterial properties without unfavorable cytotoxic effects towards eukaryotic cells in vitro. These promising preliminary results indicate that obtained C60 fullerenol-gentamicin conjugate could have biomedical potential. It may be presumed that obtained fullerenol may be used as an effective carrier for antibiotic, and developed fullerenol-gentamicin conjugate may be apply locally (i.e., at the wound site). Moreover, in future we will evaluate possibility of its applications in inter alia tissue engineering, namely as a component of wound dressings and implantable biomaterials.

Biomimetically Inspired Highly Homogeneous Hydrophilization of Graphene with Poly(l-DOPA): Toward Electroconductive Coatings from Water-Processable Paints.

Water-based processing of graphene—typically considered as physicochemically incompatible with water in the macroscale—emerges as the key challenge among the central postulates of green nanotechnology. These problematic concerns are derived from the complex nature of graphene in the family of sp2-carbon nanoallotropes. Indeed, nanomaterials hidden under the common “graphene” signboard are very rich in morphological and physicochemical variants. In this work, inspired by the adhesion chemistry of mussel biomaterials, we have synthesized novel, water-processable graphene–polylevodopa (PDOPA) hybrids. Graphene and PDOPA were covalently amalgamated via the “growth-from” polymerization of l-DOPA (l-3,4-dihydroxyphenylalanine) monomer in air, yielding homogeneously PDOPA-coated (23 wt %) (of thickness 10–20 nm) hydrophilic flakes. The hybrids formed >1 year stable and water-processable aqueous dispersions and further conveniently processable paints of viscosity 0.4 Pa·s at 20 s–1 and a low yield stress τ0 up to 0.12 Pa, hence exhibiting long shelf-life stability and lacking sagging after application. Demonstrating their applicability, we have found them as surfactant-like nanoparticles stabilizing the larger, pristine graphene agglomerates in water in the optimized graphene/graphene–PDOPA weight ratio of 9:1. These characteristics enabled the manufacture of conveniently paintable coatings of low surface resistivity of 1.9 kΩ sq–1 (0.21 Ω·m) which, in turn, emerge as potentially applicable in textronics, radar-absorbing materials, or electromagnetic interference shielding.

Comparison of Different Commercial Nanopolystyrenes: Behavior in Exposure Media, Effects on Immune Function and Early Larval Development in the Model Bivalve Mytilus galloprovincialis.

In the absence of standard methods for the detection/quantification of nanoplastics (NPs) in environmental samples, commercial nanopolymers are utilized as proxies for toxicity testing and environmental risk assessment. In marine species, a considerable amount of data are now available on the effects of nanopolystyrene (PS-NPs) of different size/surface characteristics. In this work, amino modified PS-NPs (PS-NH2) (50 and 100 nm), purchased from two different companies, were compared in terms of behavior in exposure media and of biological responses, from molecular to organism level, in the model marine bivalve Mytilus. Different PS-NH2 showed distinct agglomeration and surface charge in artificial sea water (ASW) and hemolymph serum (HS). Differences in behavior were largely reflected by the effects on immune function in vitro and in vivo and on early larval development. Stronger effects were generally observed with PS-NH2 of smaller size, showing less agglomeration and higher positive charge in exposure media. Specific molecular interactions with HS components were investigated by the isolation and characterization of the NP-corona proteins. Data obtained in larvae demonstrate interference with the molecular mechanisms of shell biogenesis. Overall, different PS-NH2 can affect the key physiological functions of mussels at environmental concentrations (10 µg/L). However, detailed information on the commercial NPs utilized is required to compare their biological effects among laboratory experiments.

Nanotechnology Helps Decrease Pressure, Increase Injection in Offshore China Oil Field

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30407, “Case Study of Nanopolysilicon Materials’ Depressurization and Injection-Increasing Technology in Offshore Bohai Bay Oil Field KL21-1,” by Qing Feng, Nan Xiao Li, and Jun Zi Huang, China Oilfield Services, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2–6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Nanotechnology offers creative approaches to solve problems of oil and gas production that also provide potential for pressure-decreasing application in oil fields. However, at the time of writing, successful pressure-decreasing nanotechnology has rarely been reported. The complete paper reports nanopolysilicon as a new depressurization and injection-increasing agent. The stability of nanopolysilicon was studied in the presence of various ions, including sodium (Na+), calcium (Ca2+), and magnesium (Mg2+). The study found that the addition of nanomaterials can improve porosity and permeability of porous media. Introduction More than 600 water-injection wells exist in Bohai Bay, China. Offshore Field KL21-1, developed by water-flooding, is confronted with the following challenges: - Rapid increase and reduction of water-injection pressure - Weak water-injection capacity of reservoir - Decline of oil production - Poor reservoir properties - Serious hydration and expansion effects of clay minerals To overcome injection difficulties in offshore fields, conventional acidizing measures usually are taken. But, after multiple cycles of acidification, the amount of soluble substances in the rock gradually decreases and injection performance is shortened. Through injection-performance experiments, it can be determined that the biological nanopolysilicon colloid has positive effects on pressure reduction and injection increase. Fluid-seepage-resistance decreases, the injection rate increases by 40%, and injection pressure decreases by 10%. Features of Biological Nanopolysilicon Systems The biological nanopolysilicon-injection system was composed of a bioemulsifier (CDL32), a biological dispersant (DS2), and a nanopolysilicon hydrophobic system (NP12). The bacterial strain of CDL32 was used to obtain the culture colloid of biological emulsifier at 37°C for 5 days. DS2 was made from biological emulsifier CDL32 and some industrial raw materials described in Table 1 of the complete paper. Nanopolysilicon hydrophobic system NP12 was composed of silicon dioxide particles. The hydrophobic nanopolysilicons selected in this project featured particle sizes of less than 100 nm. In the original samples, a floc of nanopolysilicon was fluffy and uniform. But, when wet, nanopolysilicon will self-aggregate and its particle size increases greatly. At the same time, nanopolysilicon features significant agglomeration in water. Because of its high interface energy, nanopolysilicon is easily agglomerated, as shown in Fig. 1.

A novel biodegradable porous graphitic carbon nitride/poly(lactic acid) fiber photocatalyst for efficient elimination of carbamazepine under solar irradiation

Developing efficient photocatalytic materials for the elimination of emerging contaminants is of great significance for wastewater treatment. However, photocatalysts in powder form usually suffer from the problems of easy agglomeration and difficult recycle in water. Herein, graphitic carbon nitride/polylactic acid (g-C3N4/PLA) fiber composites with highly hierarchical macro/mesoporous structure were constructed by a simple and efficient methods of centrifugal-electrostatic spinning and alkali treatment. The porous structure of fiber could provide abundant space to immobilize g-C3N4 nanosheets, avoiding the wrapping of g-C3N4 inside the fiber and creating more active sites for photocatalytic reaction. Importantly, the carbamazepine (CBZ) removal rate by porous g-C3N4/PLA fiber composites under solar irradiation was as high as 99% in 2 h. The reaction mechanisms and CBZ degradation pathways were identified. Superoxide radical (•O2−), singlet oxygen (1O2) and hole (h+) were regarded as dominant active species in porous g-C3N4/PLA photocatalytic system for photocatalytic degradation of CBZ. The porous fiber composites not only possessed superior photocatalytic activity, repeatability and stability, but also could be biodegraded in natural environment without secondary pollution. This work proposed a promising way for developing efficient, stable and environmental-friendly photocatalytic materials for the removal of CBZ and other emerging contaminants in wastewater.

Ti3C2Tx/rGO porous composite films with superior electromagnetic interference shielding performances

Inspired by successful construction of porous structure between graphene layers and the similarity in structures of Ti3C2Tx and graphene, a novel method was proposed to prepare Ti3C2Tx-based porous electromagnetic interference (EMI) shielding composite films with the assistance of graphene oxide (GO). Ti3C2Tx/rGO porous EMI shielding composite films were then prepared by ion-induced self-assembly & vacuum-assisted filtration. The structure of Ti3C2Tx/rGO porous composite films presented to be dense in surface and porous inside. Due to the synergy of high electrical conductivity (σ) and porous structure, when the mass ratio of GO to Ti3C2Tx was 2:2, the EMI shielding effectiveness (SE) of Ti3C2Tx/rGO porous composite films reached the maximum (59 dB), and the corresponding specific SE (SSE/t) reached 37619 dB cm2 g−1 (the highest value reported in similar materials). Meanwhile, the obtained Ti3C2Tx/rGO porous composite films were more hydrophobic than Ti3C2Tx film, beneficial for reducing the oxidation caused by water agglomeration on surface. Our prepared Ti3C2Tx/rGO porous composite films present superior thermal stability, σ & EMI shielding performance and environmental stability, which show great potential application in the fields of ultra-thin, light and flexible EMI shielding materials as well as highly sensitive and flexible instruments and equipments.

Influence of Water Flow Velocity on the Formation of Algae-induced Odorous Black Water Agglomerate

Wang, G.F.; Fang, Y.; Li, X.N., and Xue, J.P., 2020. Influence of water flow velocity on the formation of algae-induced odorous black water agglomerate. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 478–485. Coconut Creek (Florida), ISSN 0749-0208.Flow velocity is the most basic and intuitive factor to characterize hydrodynamic conditions. In this study, the formation characteristics of algae-induced odorous black water agglomerate under different water flow velocities were observed and analyzed, by simulating the dynamic process of water flow in Taihu lake. The experiment lasted for 20 days. The results revealed that the increase of flow velocity had different effects on the stinking and blackening of water. With the increase of the flow velocity, the concentration of Dimethyl trisulfide, an odorous matter, decreased sharply, and the concentration of β-ionone increased slightly. In terms of water blackening, compared with the flow velocity of 5∼6cm/s, the water flow velocity of 1∼2cm/s did not influence the anaerobic reduction environment of water, but promoted the formation of sulfide and the dissolution of Fe2+, accelerated the formation of blackening causing substances, and aggravated the water blackening. Low water velocity would be a key factor to promote the occurrence of the algae-induced odorous black water agglomerate and could be used as a warning factor.

Reliance and effect of sediment bulking on the physicochemical properties of sediments in aquatic environments

Sediment bulking is intently related to the occurrence of black water agglomerate, sediment resuspension and erosion in aquatic environments. In this study, five different lake sediments were sampled to study effects of sediment characteristics on sediment bulking and then investigate how sediment bulking affected in turn sediment physicochemical properties. Within 30 days of experiments, the sediment properties showed an obvious influence on variation in sediment height (VSH) ranging from only 0.03 to 1.26 cm for five sediment samples. It was found that labile nutrients were closely related to the VSH (P < 0.05) during sediment bulking. In addition, the high-throughput sequencing revealed that the microbial communities in sediments associated with degradation of organic matter and anaerobic environments, were also related to sediment bulking. Through comparing sediments with and without bulking, it was found that sediment bulking would clearly increase the proportion of air around 2.14 times, and reduce the critical shear stress of sediment with a decrease by 67.33% after 30 days, which favored sediment resuspension and erosion. Thus, this study could provide a deep insight in the key factors and the environmental effects of sediment bulking, and then be helpful in protecting the aquatic environments against ecological disasters.

Real-time monitoring of sediment bulking through a multi-anode sediment microbial fuel cell as reliable biosensor

Sediment bulking was closely related to the occurrence of black water agglomerate in anoxic aquatic sediments. Real-time monitoring of sediment bulking can be labor intensive and technically difficult, especially in dynamic environments where a record of variation in height over time is desired. In this study, a vertically distributed multi-anodes sediment microbial fuel cell (SMFC) as biosensor was developed for monitoring the changes in sediment height. According to the principle of sediment microbial fuel cell (SMFC), the voltage of SMFC would increase when the anode embedded into the sediment. The results showed that when the anode buried in the sediment, the biosensing system delivered voltage can increase to 40 mV, where the power density of SMFC exceeded 10 mW m−2 with overshoot of power density appeared. However, for the anodes above the water-sediment interface, the voltages and power densities kept at around 0. The redundancy analysis further indicated that the labile carbon pool-I of sediment was a key factor for sediment bulking, which led to drastic changes in sediment characteristics. The results from this study can provide a simple strategy for identifying sediment bulking in shallow lakes.

Partially Dissociated Water Dimers at the Water–Hematite Interface

The oxygen evolution reaction (OER) is thought to occur via a four-step mechanism with *O, *OH, and *OOH as adsorbed intermediates. Linear scaling of the *OH and **OOH adsorption energies is proposed to limit the oxides’ efficiency as OER catalysts, but the use of simple descriptors to screen candidate materials neglects potentially important water–water interactions. Here, we use a combination of temperature-programmed desorption (TPD), X-ray photoemission spectroscopy (XPS), noncontact atomic force microscopy (nc-AFM), and density functional theory (DFT)-based computations to show that highly stable HO–H2O dimer species form at the (1102) facet of hematite; a promising anode material for photoelectrochemical water splitting. The UHV-based results are complemented by measurements following exposure to liquid water and are consistent with prior X-ray scattering results. The presence of strongly bound water agglomerates is generally not taken into account in OER reaction schemes but may play a role in det...

Suppression of the Thermal Decomposition Reaction of Forest Combustible Materials in Large-Area Fires

Experimental investigations on the characteristic time of suppression of the thermal decomposition reaction of typical forest combustible materials (aspen twigs, birch leaves, spruce needles, pine chips, and a mixture of these materials) and the volume of water required for this purpose have been performed for model fire hotbeds of different areas: SFCM = 0.0003–0.007 m2 and SFCM = 0.045–0.245 m2. In the experiments, aerosol water flows with droplets of size 0.01–0.25 mm were used for the spraying of model fire hotbeds, and the density of spraying was 0.02 L/(m2·s). It was established that the characteristics of suppression of a fire by an aerosol water flow are mainly determined by the sizes of the droplets in this flow. Prognostic estimates of changes in the dispersivity of a droplet cloud, formed from large (as large as 0.5 L) "drops" (water agglomerates) thrown down from a height, have been made. It is shown that these changes can influence the conditions and characteristics of suppression of a forest fire. Dependences, allowing one to forecast the characteristics of suppression of the thermal decomposition of forest combustible materials with the use of large water agglomerates thrown down from an aircraft and aerosol clouds formed from these agglomerates in the process of their movement to the earth, are presented.

Mobility and settling rate of agglomerates of polydisperse nanoparticles.

Agglomerate settling impacts nanotoxicology and nanomedicine as well as the stability of engineered nanofluids. Here, the mobility of nanostructured fractal-like SiO2 agglomerates in water is investigated and their settling rate in infinitely dilute suspensions is calculated by a Brownian dynamics algorithm tracking the agglomerate translational and rotational motion. The corresponding friction matrices are obtained using the HYDRO++ algorithm [J. G. de la Torre, G. del Rio Echenique, and A. Ortega, J. Phys. Chem. B 111, 955 (2007)] from the Kirkwood-Riseman theory accounting for hydrodynamic interactions of primary particles (PPs) through the Rotne-Prager-Yamakawa tensor, properly modified for polydisperse PPs. Agglomerates are generated by an event-driven method and have constant mass fractal dimension but varying PP size distribution, mass, and relative shape anisotropy. The calculated diffusion coefficient from HYDRO++ is used to obtain the agglomerate mobility diameter dm and is compared with that from scaling laws for fractal-like agglomerates. The ratio dm/dg of the mobility diameter to the gyration diameter of the agglomerate decreases with increasing relative shape anisotropy. For constant dm and mean dp, the agglomerate settling rate, us, increases with increasing PP geometric standard deviation σp,g (polydispersity). A linear relationship between us and agglomerate mass to dm ratio, m/dm, is revealed and attributed to the fast Brownian rotation of such small and light nanoparticle agglomerates. An analytical expression for the us of agglomerates consisting of polydisperse PPs is then derived, us=1-ρfρpg3πμmdm (ρf is the density of the fluid, ρp is the density of PPs, μ is the viscosity of the fluid, and g is the acceleration of gravity), valid for agglomerates for which the characteristic rotational time is considerably shorter than their settling time. Our calculations demonstrate that the commonly made assumption of monodisperse PPs underestimates us by a fraction depending on σp,g and agglomerate mass mobility exponent. Simulations are in excellent agreement with deposition rate measurements of fumed SiO2 agglomerates in water.