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1
Priyadarshini, N., M. Sampath, Shekhar Kumar, U. Kamachi Mudali et R. Natarajan. « Probing Uranium(IV) Hydrolyzed Colloids and Polymers by Light Scattering ». Journal of Nuclear Chemistry 2014 (26 mars 2014) : 1–10. http://dx.doi.org/10.1155/2014/232967.
Texte intégralRésumé :
Tetravalent uranium readily undergoes hydrolysis even in highly acidic aqueous solutions. In the present work, solutions ranging from 0.4 to 19 mM (total U) concentration (1<pH<4) are carefully investigated by light scattering technique with special emphasis on polymerization leading to colloid formation. The results clearly indicate that the concentration has significant effect on particle size as well as stability of colloids. With increasing concentration the size of colloids formed is smaller due to more crystalline nature of the colloids. Stability of colloids formed at lower concentration is greater than that of colloids formed at higher concentration. Weight average molecular weight of the freshly prepared and colloidal polymers aged for 3 days is determined from the Debye plot. It increases from 1,800 to 13,000 Da. 40–50 atoms of U are considered to be present in the polymer. Positive value of second virial coefficient shows that solute-solvent interaction is high leading to stable suspension. The results of this work are a clear indication that U(IV) hydrolysis does not differ from hydrolysis of Pu(IV).
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Kurosawa, S., et S. Ueta. « Effect of colloids on radionuclide migration for performance assessment of HLW disposal in Japan ». Pure and Applied Chemistry 73, no 12 (1 janvier 2001) : 2027–37. http://dx.doi.org/10.1351/pac200173122027.
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Colloidal effect is one of the major factors to enhance the migration of radionuclides in groundwater. The experimental and theoretical studies of colloid mobility and colloid-facilitated radionuclide transport for the performance assessment of high-level radioactive waste (HLW) geological disposal is presented in this paper. The major aims of the study are (1) to study the filtration effect on colloids by the engineered barrier system, (2) to study bentonite colloid generation by erosion of the engineered barrier system, and (3) to calculate radionuclide migration with groundwater colloids through fractured rock systems. Alternative coagulants based on prehydrolyzed forms of aluminium or iron can be more effective than the traditional materials in many cases, but their mode of action is not completely understood, especially with regard to the role of charge neutralization and hydroxide precipitation. Basic principles of colloid stability and metal ion hydrolysis are briefly reviewed, and the action of hydrolyzing metal coagulants is then discussed, with some examples from recent experimental studies. Although it is possible to interpret results reasonably well in terms of established ideas, there are still some uncertainties that need to be resolved
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Sasamoto, Hiroshi, et Shingo Onda. « Preliminary results for natural groundwater colloids in sedimentary rocks of the Horonobe Underground Research Laboratory, Hokkaido, Japan ». Geological Society, London, Special Publications 482, no 1 (7 septembre 2018) : 191–203. http://dx.doi.org/10.1144/sp482.1.
Texte intégralRésumé :
AbstractColloid concentration is an important parameter in models of colloid-facilitated transport. The purpose of the present study is to characterize colloid concentrations and colloid stability in natural groundwater from the Horonobe Underground Research Laboratory (URL) in Hokkaido, Japan. The particle sizes of colloids in groundwaters from the Horonobe URL range from several nanometres to c. 500 nm, with a mode particle size of c. 120 nm. Evaluation of colloid stability by DLVO theory suggests that larger colloids (i.e. >100 nm in diameter) would be more stable than smaller colloids in some groundwaters. The estimated colloid particle concentrations when considering the results of DLVO calculations ranged from 2.33 × 106 to 1.12 × 108 particles/ml, and mass concentrations were estimated to range from 45 to 1540 µg l−1 for diameters greater than 100 nm. Colloids in Horonobe groundwaters appear to be less stable, with a moderate potential for transport, than colloids investigated in similar international studies. This reduced stability may be due to relatively higher ionic strengths and moderate dissolved organic concentrations in Horonobe groundwaters compared to their international counterparts.
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Kashyap, Swarnima, Shashank Mishra et Shantanu K. Behera. « Aqueous Colloidal Stability of Graphene Oxide and Chemically Converted Graphene ». Journal of Nanoparticles 2014 (13 novembre 2014) : 1–6. http://dx.doi.org/10.1155/2014/640281.
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Graphene oxide (GO) was prepared by modified Hummer’s method, and chemically converted graphene (CCG) was prepared by further reduction of the aqueous GO colloid. The effect of pH on particle size, particle charge, and light absorption of the aqueous colloids of GO and CCG was studied with titration against HCl or NaOH, to find the ideal characteristics for a stable dispersion. The GO colloid was stable in the pH range of 4–11, whereas the CCG colloid gained stability at a relatively narrower pH range of 7–10. Poor stability of the colloids was observed for both GO and CCG colloids at both extremes of the pH scale. Both of the colloids exhibited average size of ~1 micron in the low pH range, whereas for higher pH the size ranged between 300 and 500 nm. The UV-Vis spectra showed absorption peak at 230 nm for GO colloids that shifted to 260 nm for the CCG colloid. Such shift can be ascribed to restoring of electronic conjugation of the C=C bonds in CCG.
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Kalnina, Daina, Kārlis Agris Gross, Artur Medvids et Pavels Onufrijevs. « Formation of Negatively Charged AgI Colloid Nanoparticles by Condensation ». Advanced Materials Research 1117 (juillet 2015) : 159–63. http://dx.doi.org/10.4028/www.scientific.net/amr.1117.159.
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The stability of silver halide colloids is reported to be important for the toxicological outcome. This study shows a well-suited and cheap condensation reaction to obtain negatively charged silver iodide (AgI) nanoparticles without additional stabilization agents. Charged AgI colloids were synthesized from silver nitrate and potassium iodide solutions. An excess of potassium iodide not only imparted a negative charge, but provided a narrow particle size distribution (50 ± 10 nm). The change of optical properties in the colloid was investigated by UV-VIS spectroscopy. A silver iodide exciton absorption band at peak ~421nm (2.93eV), red-shifted over time. The peak at half maximum intensity increased from 13.3nm to 14.8 nm, characterizing the dispersity of AgI colloidal particles. Colloidal particles stabilized after 33 hours. In-situ real-time UV-VIS measurements provide a tool to adjust the particle characteristics and may serve to further optimize the performance in biological applications.
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Liu, Yongliang, Yud-Ren Chen, Xiangwu Nou et Kuanglin Chao. « Potential of Surface-Enhanced Raman Spectroscopy for the Rapid Identification of Escherichia Coli and Listeria Monocytogenes Cultures on Silver Colloidal Nanoparticles ». Applied Spectroscopy 61, no 8 (août 2007) : 824–31. http://dx.doi.org/10.1366/000370207781540060.
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Surface-enhanced Raman (SERS) spectra of various batches of bacteria adsorbed on silver colloidal nanoparticles were collected to explore the potential of the SERS technique for rapid and routine identification of E. coli and L. monocytogenes cultures. Relative standard deviation (RSD) of SERS spectra from silver colloidal suspensions and ratios of SERS peaks from small molecules (K3PO4) were used to evaluate the reproducibility, stability, and binding effectiveness of citrate-reduced silver colloids over batch and storage processes. The results suggested consistent reproducibility of silver colloids over batch process and also stability and consistent binding effectiveness over an eight-week storage period. A variety of mixtures of E. coli/L. monocytogenes cultures with different colloidal batches revealed that, despite large variations in relative intensities and positions of SERS active bands, characteristic and unique bands at 712 and 390 cm−1 were consistently observed and were the strongest in E. coli and L. monocytogenes cultures, respectively. Two specific bands were used to develop simple algorithms in the evaluation of binding effectiveness of silver colloids over storage and further to identify E. coli and L. monocytogenes cultures with a 100% success. A single spectrum acquisition took 5∼6 min, and a minimum of 25 μL silver colloid was directly mixed with 25 μL volume of incubated bacterial culture. The short acquisition time and small volume of incubated bacterial culture make silver colloidal nanoparticle based SERS spectroscopy ideal for potential use in the routine and rapid screening of E. coli and L. monocytogenes cultures on large scales. This is the first report of the development of simple and universal algorithms for bacterial identification from the respective exclusive SERS peaks.
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Bolotov, Alexander N., Vladislav V. Novikov et Olga O. Novikova. « ON DEPENDENCE OF COLLOIDAL STABILITY OF MAGNETIC LIQUID ON STABILIZER DIELECTRIC CAPACITIVITY AND DISPERSION MEDIUM ». IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA 60, no 4 (12 mai 2017) : 75. http://dx.doi.org/10.6060/tcct.2017604.5506.
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The purpose of this article is to research the possibility of using values of stabilizer dielectric capacitivity and dispersion medium to form a colloidal stability criterion of magnetic liquid. The authors researched colloidal stability of magnetic liquids with a low-polarity base, nonionogenous SAM-stabilizer (oligoester) and hydroximag nanoparticles. The received magnetic colloids were tested for stability in a gravity field to evaluate SAM stabilizing capacity. The authors propose Е-criterion that shows a relative difference between dielectric capacitivities of a dispersion medium and SAM-stabilizer. It was determined that such combination of dielectric capacitivity of solution component parts correlates with the values of SAM adsorption and colloid stability in the best way. The test results show that relative reduction of magnetization correlates well with a value of dispersion medium dielectric capacitivity due to irreversible sedimentative processes. In the next set of experiments, the authors did not change the magnetic colloid liquid content, but SAM-stabilizer. They research the dependence of colloidal stability of magnetic liquids based on a dioctyl sebacate of a stabilized SAM with various dielectric capacitivities. The test results prove regularity of increasing colloidal stability with decreasing E- criterion. The paper considers in details the physical and chemical mechanisms that help to develop the influence of dielectric capacitivity on magnetic liquid colloidal stability. The analysis of testing results showed that dielectric capacitivity of magnetic liquid components affects many physical-chemical phenomenons in the process of its synthesis. It is important that the behaviour of sorption processes on the surface of dispersed particles depends on dielectric capacitivity. The result of the empirical data research by magnetic liquid colloidal stability shows that with increasing dielectric capacitivity of dispersion medium in relation to stabilizer’s dielectric capacitivity the desorption processes of stabilizer’s molecules from a magnetic particles’ surface increses. As a result, the adsorption layer around particles becomes more incoherent and less competent. It reduces the value of a steric stabilization factor of a magnetic liquid colloidal structure. In practice it leads to deterioration or even loss of colloidal stability of magnetic liquid. The influence of dielectric capacitivity on colloidal stability using the effects of interparticle interaction is less important. To summarize, the article proves a dielectric E-criterion that can be used to provide rationale for the choice of SAM-stabilizer for magnetic liquids. According to this criterion, dielectric capacitivity of a dispersion medium should be slightly different from the similar property of SAM-stabilizer. Otherwise, molecule desorption processes of SAM from magnetic particles encourage quality degradation of covering adsorption layers, so colloidal stability worsens.Forcitation:Bolotov A.N., Novikov V.V., Novikova O.O. On dependence of colloidal stability of magnetic liquid on stabilizer dielectric capacitivity and dispersion medium. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 75-81.
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Roto, Roto, Hani Prima Rasydta, Adhitasari Suratman et Nurul Hidayat Aprilita. « Effect of Reducing Agents on Physical and Chemical Properties of Silver Nanoparticles ». Indonesian Journal of Chemistry 18, no 4 (12 novembre 2018) : 614. http://dx.doi.org/10.22146/ijc.26907.
Texte intégralRésumé :
Silver nanoparticles having uniform size and shape, a diameter range of 10–50 nm, excellent stability, and high zeta potential are always desirable for many applications. The silver nanoparticles were synthesized by chemical reduction method using some reducing agents in a polyvinyl alcohol solution. This study aims at determining the effect of reducing agents on the chemical and physical properties of silver nanoparticles. Ascorbic acid, sodium borohydride, hydrazine, sodium citrate, and glucose were used as reducing agents. Surface Plasmon Resonance (SPR) absorbance, morphology, zeta potential, crystal system, and stability of the products were studied. The results showed that the chemical and physical properties of the colloidal Ag nanoparticles were dependent on the reducing agents. In general, the produced silver nanoparticles have an fcc crystal system with a unit cell of 4.0906–4.0992 Å. The SPR absorbance of the colloids has the peak in the range of 401–433 nm. We found that the colloid of silver nanoparticles prepared by using ascorbic acid has uniform spherical shape, the diameter of about 20 nm, and zeta potential of -10.4 mV. After being stored for one month, the SPR absorbance of the colloid decreased by only 5%. This type of colloidal Ag nanoparticles prepared by using ascorbic acid is expected to be used for chemical sensors, an antibacterial agent, and so on.
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Макаров, А. С., Н. А. Шмигельская et В. А. Максимовская. « The effect of using gum arabic on the quality of different types of wines ». Magarach Vinogradstvo i Vinodelie, no 1(119) (24 mars 2022) : 84–89. http://dx.doi.org/10.35547/im.2022.54.77.013.
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Систематизированы литературные данные о влиянии защитного коллоида гуммиарабика на сроки стабильности различных типов вин (игристых, ликерных). Показано, что применение защитных коллоидов способствует увеличению сроков стабильности игристых и ликерных вин против кристаллических и коллоидных (обратимых и необратимых) помутнений. Уточнено, что в состав гуммиарабика входят полисахариды, построенные из арабинозы, галактозы, рамнозы, галактуроновой и глюкуроновой кислот. Сделан вывод о том, что роль защитных коллоидов выполняют кислые полисахариды, содержащиеся в гуммиарабике. Показано, что при обработке виноматериалов для игристых вин защитным коллоидом коэффициент сопротивления виноматериала выделению диоксида углерода повышается на 20 %, скорость разрушения пены снижается на 14%, максимальный объем пены увеличивается на 7 %, что способствует улучшению пенистых и игристых свойств готовой продукции. Установлено, что при добавлении 500 мг/дм гуммиарабика в игристое вино его пенистые и игристые свойства повышаются в среднем на 40%. Применение гуммиарабика способствует повышению сроков стабильности игристых и крепленых вин против кристаллических и коллоидных помутнений. Literature data about the effect of protective colloid of gum arabic on the terms of stability of various types of wines (sparkling, liqueur) were systematized. It was shown that using of protective colloids contributed to an increase in the stability of sparkling and liqueur wines against crystalline and colloidal (reversible and irreversible) haze. It was also clarified that gum arabic contained polysaccharides developed from arabinose, galactose, rhamnose, galacturonic and glucuronic acids. It was concluded that the role of protective colloids was played by acidic polysaccharides contained in gum arabic. It is shown that when base wines for sparklings are treated with a protective colloid, the coefficient of base wine resistance to the release of carbon dioxide increases by 20%, the rate of foam break decreases by 14%, the maximum volume of foam increases by 7%, which contributes to the improvement of foamy and sparkling properties of the finished product. It is established that adding 500 mg/dm of gum arabic to sparkling wine increases its foamy and sparkling properties by an average of 40%. The use of gum arabic contributes to an increase in stability of sparkling and fortified wines against crystalline and colloidal haze.
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Drzewiński, Andrzej, Maciej Marć, Wiktor W. Wolak et Mirosław R. Dudek. « Effect of Magnetic Heating on Stability of Magnetic Colloids ». Nanomaterials 12, no 17 (3 septembre 2022) : 3064. http://dx.doi.org/10.3390/nano12173064.
Texte intégralRésumé :
Stable aqueous suspension of magnetic nanoparticles is essential for effective magnetic hyperthermia and other applications of magnetic heating in an alternating magnetic field. However, the alternating magnetic field causes strong agglomeration of magnetic nanoparticles, and this can lead to undesirable phenomena that deteriorate the bulk magnetic properties of the material. It has been shown how this magnetic field influences the distribution of magnetic agglomerates in the suspension. When investigating the influence of the sonication treatment on magnetic colloids, it turned out that the hydrodynamic diameter as a function of sonication time appeared to have a power-law character. The effect of magnetic colloid ageing on magnetic heating was discussed as well. It was shown how properly applied ultrasonic treatment could significantly improve the stability of the colloid of magnetic nanoparticles, ultimately leading to an increase in heating efficiency. The optimal sonication time for the preparation of the magnetic suspension turned out to be time-limited, and increasing it did not improve the stability of the colloid. The obtained results are important for the development of new materials where magnetic colloids are used and in biomedical applications.
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Stiufiuc, Rares, Cristian Iacovita, Raul Nicoara, Gabriela Stiufiuc, Adrian Florea, Marcela Achim et Constantin M. Lucaciu. « One-Step Synthesis of PEGylated Gold Nanoparticles with Tunable Surface Charge ». Journal of Nanomaterials 2013 (2013) : 1–7. http://dx.doi.org/10.1155/2013/146031.
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The present work reports a rapid, simple and efficient one-step synthesis and detailed characterisation of stable aqueous colloids of gold nanoparticles (AuNPs) coated with unmodified poly(ethylene)glycol (PEG) molecules of different molecular weights and surface charges. By mixing and heating aqueous solutions of PEG with variable molecular chain and gold(III) chloride hydrate (HAuCl4) in the presence of NaOH, we have successfully produced uniform colloidal 5 nm PEG coated AuNPs of spherical shape with tunable surface charge and an average diameter of 30 nm within a few minutes. It has been found out that PEGylated AuNPs provide optical enhancement of the characteristic vibrational bands of PEG molecules attached to the gold surface when they are excited with both visible (532 nm) and NIR (785 nm) laser lines. The surface enhanced Raman scattering (SERS) signal does not depend on the length of the PEG molecular chain enveloping the AuNPs, and the stability of the colloid is not affected by the addition of concentrated salt solution (0.1 M NaCl), thus suggesting their potential use forin vitroandin vivoapplications. Moreover, by gradually changing the chain length of the biopolymer, we were able to control nanoparticles’ surface charge from −28 to −2 mV, without any modification of the Raman enhancement properties and of the colloidal stability.
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Bovin, Jan-Olov. « The temperature stability of ligand stabilized gold and bimetallic colloids ». Proceedings, annual meeting, Electron Microscopy Society of America 50, no 1 (août 1992) : 296–97. http://dx.doi.org/10.1017/s0424820100121880.
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Preparation and characterization of new monodispersed clusters and colloids of different metals are important for use in several applications like catalysis, microelectronics and sintering. The atomic structure of ligand stabilized, 18 nm, gold colloid is important, since they can serve as the core in preparation of bimetallic systems. The recent developments in preparative cluster chemistry have made it possible to make 35 nm bimetallic layered colloids of gold-platinum and gold-palladium. If the colloids should be useful as catalysts, it is important to establish their thermal stability and structure at the elevated temperatures where catalytic reactions take place. The first preliminary results from a high temperature study in an electron microscope with a heating stage are presented here.
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Zhanpeng, Jiang, et Guan Yuntao. « Flocculation morphology : effect of particulate shape and coagulant species on flocculation ». Water Science and Technology 53, no 7 (1 mars 2006) : 9–16. http://dx.doi.org/10.2166/wst.2006.202.
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Flocculation morphology is a new concept that investigates the morphological characteristics of colloidal particles and coagulants in water during the flocculation process, and the influence that these characteristics have on flocculation process efficiency. This paper is a summary of advances in research on this topic over several years. Morphological characteristics of colloids in natural waters and different kinds of hydrolysed coagulants are investigated, and their effect on colloid stability, flocculation kinetics and efficiency is analysed. It is confirmed that the traditional theory has some deviations in coagulation of nonspherical particles, and these deviations are revised by the flocculation morphology model. Flocculation morphology can not only promote research about flocculation theory, but also instruct the production, application and flocculation control. It can be foreseen that more progress will be made in research and application of flocculation morphology in the near future.
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Forcada, Jacqueline, et Roque Hidalgo-Alvarez. « Functionalized Polymer Colloids : Synthesis and Colloidal Stability ». Current Organic Chemistry 9, no 11 (1 juillet 2005) : 1067–84. http://dx.doi.org/10.2174/1385272054368484.
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Homoky, William B., Tim M. Conway, Seth G. John, Daniela König, FeiFei Deng, Alessandro Tagliabue et Rachel A. Mills. « Iron colloids dominate sedimentary supply to the ocean interior ». Proceedings of the National Academy of Sciences 118, no 13 (26 mars 2021) : e2016078118. http://dx.doi.org/10.1073/pnas.2016078118.
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Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δ56Fe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δ56Fe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a “rusty source”) that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.
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Grybos, Malgorzata, Delphine Masson, Pauline Gorgeon, Patrice Fondanèche, Nicolas Martin, Fabrice Dupuy, Emmanuel Joussein et Valentin Robin. « Bioavailability of Colloidal Iron to Heterotrophic Bacteria in Sediments, and Effects on the Mobility of Colloid-Associated Metal(loid)s ». Minerals 12, no 7 (25 juin 2022) : 812. http://dx.doi.org/10.3390/min12070812.
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The submicrometric fraction of surface sediments that accumulate in the bottom of dam reservoirs represent important sources of nutrients and contaminants in freshwater systems. However, assessing their stability in the presence of sediment bacteria as well as their bioavailability in the sediment remains poorly understood. We hypothesized that sediment’s bacteria are able to extract nutrients from sedimentary colloids (<1 µm fraction) and thus contribute to the release of other colloid-associated elements to water. Experiments were performed under laboratory conditions, using the submicrometric fractions of sediments recovered from two dam reservoirs (in calcareous and crystalline granitic contexts) and two heterotrophic bacteria (Gram-negative Pseudomonas sp. and Gram-positive Mycolicibacterium sp.). The results demonstrated that bacteria were able to maintain their metabolic activity (the acidification of the growth medium and the production of organic ligands) in the presence of colloids as the sole source of iron (Fe) and regardless of their chemical composition. This demonstrates that bioavailable Fe, aside from ionic forms, can also occur in colloidal forms. However, the bacteria also catalyzed the release of potentially toxic metallic elements (such as Pb) associated with colloids. These results help improve our understanding of the processes that influence contaminants’ mobility in the ecosystems as well as provide an important insight into current research evaluating the bioavailability of different forms of nutrients.
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Felipe-Sotelo, M., A. E. Milodowski et N. D. M. Evans. « Inhibition of the formation and stability of inorganic colloids in the alkaline disturbed zone of a cementitious repository ». Mineralogical Magazine 79, no 6 (novembre 2015) : 1419–31. http://dx.doi.org/10.1180/minmag.2015.079.6.17.
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AbstractThe generation and stability of inorganic colloids have been studied under hyperalkaline conditions. For the generation of colloids, intact cores of Bromsgrove Sandstone were flushed with simulated cement leachates, and the eluates were ultrafiltered sequentially (12 μm, 1 μm, 0.1 μm and 30 kDa) for the separation of any colloids found. No colloid formation was observed during the experiments; however the analysis by ICPMS of the eluates showed significant increases in Si and Al, indicating silicate mineral dissolution, as well as reduction of the concentration of Ca in the leachates indicating precipitation of secondary Ca-rich phases. Flow experiments with cement leachates spiked with tritiated water showed a noticeable reduction of the porosity of the sandstone as well as changes in the pore distribution. Additional stability experiments were carried out using model silica and Fe2O3 colloids. The experiments indicated that the stability of the colloids was mainly controlled by the concentration of Ca in solution and that both types were unstable under the chemical conditions in the alkaline disturbed zone. The presence of cement additives such as superplasticisers could enhance the stability of the colloids.
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ALAM, FAHAD, SAJID ALI ANSARI, WASI KHAN, M. EHTISHAM KHAN et A. H. NAQVI. « SYNTHESIS, STRUCTURAL, OPTICAL AND ELECTRICAL PROPERTIES OF IN-SITU SYNTHESIZED POLYANILINE/SILVER NANOCOMPOSITES ». Functional Materials Letters 05, no 03 (septembre 2012) : 1250026. http://dx.doi.org/10.1142/s1793604712500269.
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Polyaniline (PANI) is recognized as one of the most important conducting polymers due to its high conductivity and good stability. In this paper, polyaniline/silver (PANI/Ag) nanocomposites were synthesized by in-situ polymerization of aniline using ammonium peroxydisulphate (APS) as oxidizing agent with varying concentration of Ag nanoparticles colloids (0 ml, 25 ml and 50 ml). Silver nanoparticles were synthesized separately in colloidal form from silver nitrate (Ag2NO3) with the help of reducing agent sodium borohydride (NaBH4). The PANI/ Ag nanocomposites were characterized by XRD, SEM, AFM, UV-visible, temperature dependent resistivity and dielectric measurements. All samples show a single phase nature of the nanoparticles. The electrical resistivity as function of temperature was measured in the temperature range 298–383 K, which indicates a semiconducting to metallic transition at 373 K and 368 K for 25 ml and 50 ml silver colloid samples, respectively.
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Shang, Shu Bo, et Xu Qian Li. « Study on the Co-Migration of Pb with Soil Colloids under Rainfall ». Advanced Materials Research 183-185 (janvier 2011) : 437–41. http://dx.doi.org/10.4028/www.scientific.net/amr.183-185.437.
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In this experiment, clay loam, fine sandy loam and silty loam collected from the farmland (FL), floodplain (FP) and Loess platform (LP) in Changchun separately were chosen to study the role of rainfall on the migration of heavy metal (Pb)-colloid complexes quantitively through soil column simulation in laboratory. The purpose of this study is to illuminate the tendency for colloid-Pb co-migrating to deep soil and groundwater. The study shows whether how the mechanism between colloid and heavy metal acts, the processes exist in common. First, through some sort of adsorption, heavy metal form complexes with colloids, and co-migrate in the underground environment, which is called a co-migration mechanism. And Pb migrated out the FL, LP, and FP soil column contain 28.4%、25.7% and 22.6% complexes separately. Second, the heavy metal complexes with colloids have a certain stability and mobility. Third, in migrating process, the presence of colloids increases the migration concentration and amount of heavy metal (Pb). And the quantitative of Pb migrated out the FL, LP and FP soil column which added colloids are 1.37、1.36 and 1.25 double control columns separately. Forth, the presence of colloids reduces the reduction ability heavy metal (Pb), and shortens the consumption time for heavy metal (Pb) migrating to a certain depth of groundwater. And the time consuming of Pb migrating to groundwater with same deep is Loess horizon>floodplain horizon>farmland horizon.
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Vutukuri, Hanumantha Rao, Johan Stiefelhagen, Teun Vissers, Arnout Imhof et Alfons van Blaaderen. « Bonding Assembled Colloids without Loss of Colloidal Stability ». Advanced Materials 24, no 3 (12 décembre 2011) : 412–16. http://dx.doi.org/10.1002/adma.201104010.
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Tseng, Kuo-Hsiung, Chaur-Yang Chang, Mei-Jiun Chen et Yi-Kai Tseng. « Novel electrical discharge machining system with real-time control and monitoring for preparing nanoiron colloid ». Advances in Mechanical Engineering 10, no 8 (août 2018) : 168781401879170. http://dx.doi.org/10.1177/1687814018791705.
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Nanoiron colloid is remarkably suitable for medical, engineering, and other applications because it exhibits excellent properties such as nontoxicity, biocompatibility, and high chemical stability. Because no studies have examined preparation of nanoiron colloid through electric spark discharge method, an electrical discharge machining system for preparing nanoiron colloid was developed in this study based on automated electric spark discharge method with real-time monitoring. An Arduino microcontroller, laser positioning technology, and closed-loop motor control were combined for automatic alignment of the two discharge electrodes. This electrode alignment method enabled achieving electrode alignment accuracy of 0.139 mm. The real-time monitoring applied the Ziegler–Nichols method with a proportional–integral–derivative controller for closed-loop control of the interelectrode gap that, compared with the manually tuned proportional–integral–derivative controller, increased the interelectrode gap discharge success rate from 22.25 to 28.99. A user-friendly interface and process parameters were realized through VisSim software, an Arduino microcontroller, and an RT/DAC4 PCI card. This design enabled obtaining data on process efficiency and providing real-time process diagnosis. Compared with colloids prepared using chemical methods, the nanoiron colloids prepared in this study contained only iron and oxygen; therefore, they would be safer for application in the human body. According to the UV-Vis and Zetasizer analyses, the absorbance peak of the nanoiron colloid prepared with this system ranged from 200 to 220 nm, and the zeta potential was approximately –11.6 mV with a diameter of approximately 155.9 nm. These results verified that this electrical discharge machining system can prepare nanoiron colloid featuring excellent suspension stability.
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Mayordomo, Natalia, Claude Degueldre, Ursula Alonso et Tiziana Missana. « Size distribution of FEBEX bentonite colloids upon fast disaggregation in low-ionic strength water ». Clay Minerals 51, no 2 (mai 2016) : 213–22. http://dx.doi.org/10.1180/claymin.2016.051.2.08.
Texte intégralRésumé :
AbstractBentonite colloids generated from the backfill barrier in nuclear waste repositories may act as radionuclide carriers, if they are stable and mobile. Repository scenarios with highly saline groundwater inhibit colloid stability as particles tend to aggregate but, in the time frame of repositories, groundwater conditions may evolve, promoting particle disaggregation and stabilization. The disaggregation of FEBEX bentonite colloids by fast dilution to lower ionic strength was analysed in this study. Time-resolved dynamic light-scattering experiments were carried out to evaluate the kinetics of bentonite colloid aggregation and disaggregation processes in Na+ and Na+-Ca2+ mixed electrolytes of low ionic strength. Attachment and detachment efficiencies were determined.Aggregation is promoted by increasing ionic strength, being more efficient in the presence of divalent cations. Once bentonite colloids are aggregated, a decrease in ionic strength facilitates disaggregation, but the process is not fully reversible as the initial size of the stable bentonite colloids at low ionic strength is not fully recovered. Particle-size distribution and concentration in suspension were analysed on disaggregated samples by single particle-counting measurements. Small colloids were measured in the disaggregated samples but their population was smaller than in the initial stable sample, especially in the presence of Ca2+.
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WU-QUAN, DING, HE JIA-HONG, WANG LEI, LIU XIN-MIN et LI HANG. « EFFECT OF NONCLASSICAL POLARIZATION OF Na+ AND K+ ON THE STABILITY OF SOIL COLLOIDAL PARTICLES IN SUSPENSION ». Surface Review and Letters 24, no 07 (15 août 2017) : 1850019. http://dx.doi.org/10.1142/s0218625x18500191.
Texte intégralRésumé :
The study of soil colloids is essential because the stability of soil colloidal particles are important processes of interest to researchers in environmental fields. The strong nonclassical polarization of the adsorbed cations (Na[Formula: see text] and K[Formula: see text] decreased the electric field and the electrostatic repulsion between adjacent colloidal particles. The decrease of the absolute values of surface potential was greater for K[Formula: see text] than for Na[Formula: see text]. The lower the concentration of Na[Formula: see text] and K[Formula: see text] in soil colloids, the greater the electrostatic repulsion between adjacent colloidal particles. The net pressure and the electrostatic repulsion was greater for Na[Formula: see text] than for K[Formula: see text] at the same ion concentration. For K[Formula: see text] and Na[Formula: see text] concentrations higher than 50[Formula: see text]mmol L[Formula: see text] or 100 mmol L[Formula: see text], there was a net negative (or attractive) pressure between two adjacent soil particles. The increasing total average aggregation (TAA) rate of soil colloids with increasing Na[Formula: see text] and K[Formula: see text] concentrations exhibited two stages: the growth rates of TAA increased rapidly at first and then increased slowly and eventually almost negligibly. The critical coagulation concentrations of soil colloids in Na[Formula: see text] and K[Formula: see text] were 91.6[Formula: see text]mmol L[Formula: see text] and 47.8[Formula: see text]mmol L[Formula: see text], respectively, and these were similar to the concentrations at the net negative pressure.
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Walsch, J., et S. Dultz. « Effects of pH, Ca- and SO4-concentration on surface charge and colloidal stability of goethite and hematite – consequences for the adsorption of anionic organic substances ». Clay Minerals 45, no 1 (mars 2010) : 1–13. http://dx.doi.org/10.1180/claymin.2010.045.1.01.
Texte intégralRésumé :
AbstractSoil solution chemistry, especially pH and the presence of multivalent ions, affects the surface charge (SC) of Fe oxides and accordingly colloidal stability and sorption properties. The SC of synthetic goethite and hematite was quantified in the presence of different electrolytes (NaCl, CaCl2, Na2SO4and CaSO4) by combining the streaming potential with polyelectrolyte titration. The point of zero charge (PZC) for goethite was observed at pH 8.2 and the stability field around the PZC, where colloids are flocculated, is more extended (±1 pH unit) than that of hematite with a PZC at pH 7.1 (±0.5 pH unit). The SC decreases with increasing SO4concentration, indicating adsorption of SO4on the oxide, whereas the presence of Ca increases the SC. At pH 4, the addition of 0.1 mmol l–1Na2SO4induced a decrease in SC from 1.5 to 0.380 μmolcm–2for goethite and from 0.85 to 0.42 μmolcm–2for hematite. In a suspension with 0.1 mmol l–1Na2SO4, the number of colloids is already reduced, and both oxides flocculate rapidly and completely at >0.5 mmol l–1Na2SO4. While the addition of SO4did not affect charge titrations with the cationic polyelectrolyte, the anionic polyelectrolyte formed complexes with Ca, resulting in an overestimation of positive SC. The electrolyte CaSO4is most efficient at keeping goethite and hematite in the pH range 4–10 in the flocculated state. Besides pH, the presence of multivalent ions should also be considered when predicting colloid mediated transport and adsorption properties of anionic substances by Fe oxides in soil systems.
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Болотов, Александр Николаевич, Ольга Олеговна Новикова et Владимир Валентинович Мешков. « VISCOMETRIC STUDIES IN THE PROCESS OF SYNTHESIS OF MAGNETIC LUBRICANT NANO-OILS ». Physical and Chemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials, no 14 (15 décembre 2022) : 531–44. http://dx.doi.org/10.26456/pcascnn/2022.14.531.
Texte intégralRésumé :
В области трибологии перспективны магнитные смазочные масла, в которых для повышения их коллоидной устойчивости используют полимеры, однако их применение ограничено низкой намагниченностью коллоида. Повысить намагниченность наномасел возможно путем синтеза полимерных оболочек непосредственно на поверхности магнитных частиц в процессе получения наномасел. Описаны особенности технологии синтеза магнитных смазочных наномасел с полимерными сольватными оболочками на частицах, которые защищают их от коагуляции. Полимеризация молекул гидроксикислоты протекает по механизму поликонденсации на твердой поверхности магнетита. Вязкость магнитного коллоида возрастает из-за увеличения толщины сольватной оболочки. Исходя из этого предложено дифференциальное уравнение, которое показывает зависимость скорости роста вязкости коллоида от скорости реакции поликонденсации. Экспериментальная проверка уравнения показала, что оно выполняется с точностью до 8%. Полученное уравнение позволяет определить важную термодинамическую характеристику -энергии активации процесса синтеза полимерных оболочек на поверхности дисперсных частиц. Для расчетов нужно знать скорость изменения вязкости коллоида с дисперсионной средой без мономера (гидрокислоты). Поэтому, в процессе синтеза полимера отбираются пробы промежуточного магнитного коллоида небольшого объема, которые используются для определения вязкости коллоида и дисперсионной среды, содержащей мономер. Затем находится вязкость коллоида с чистой дисперсионной средой, необходимая для расчетов энергии активации реакции поликонденсации. По оценочным расчетам, ошибка определения энергии активации не превышает 11%. На практике, с помощью установленного значения энергии активации полимеризации, можно выполнять целенаправленный выбор оптимального температурно-временного режима стабилизации магнитного коллоида с целью получения магнитного наномасла с требуемыми характеристиками вязкости и агрегативной устойчивости. Экспериментальные исследования проводились на специально разработанных приборах для оценки коллоидной стабильности и динамической вязкости магнитных коллоидов. In the field of tribology, magnetic lubricating oils are promising, in which polymers are used to increase their colloidal stability, but their use is limited by the low magnetization of the colloid. It is possible to increase the magnetization of nanooils by synthesizing polymer shells directly on the surface of magnetic particles in the process of obtaining nanooils. The features of the technology for the synthesis of magnetic lubricating nanooils with polymeric solvation shells on particles, which protect them from coagulation, are described. Polymerization of hydroxy acid molecules proceeds by the mechanism of polycondensation on the solid surface of magnetite. The viscosity of the magnetic colloid increases due to the increase in the thickness of the solvate shell. Proceeding from this, a differential equation is proposed, which shows the dependence of the growth rate of the colloid viscosity on the rate of the polycondensation reaction. An experimental verification of the equation showed that it is fulfilled with an accuracy up to 8%. The resulting equation makes it possible to determine an important thermodynamic characteristic - the activation energy of the process of synthesis of polymer shells on the surface of dispersed particles. For calculations, it is necessary to know the rate of change in the viscosity of a colloid with a dispersion medium without a monomer (hydroacid). Therefore, in the process of the polymer synthesis, samples of the intermediate magnetic colloid of a small volume are taken, which are used to determine the viscosity of the colloid and dispersion medium containing monomers. Then the viscosity of the colloid with a pure dispersion medium is found, which is necessary for calculating the activation energy of the polycondensation reaction. According to estimates, the error in determining the activation energy does not exceed 11%. In practice, using the values of the activation energy of polymerization, it is possible to carry out a purposeful choice of the optimal temperature-time regime for stabilizing the magnetic colloid in order to obtain a magnetic nanooil with the required viscosity and aggregative stability characteristics. Experimental studies were carried out on specially designed instruments for assessing the colloidal stability and dynamic viscosity of magnetic colloids.
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Gregory, John, et Jinming Duan. « Hydrolyzing metal salts as coagulants ». Pure and Applied Chemistry 73, no 12 (1 janvier 2001) : 2017–26. http://dx.doi.org/10.1351/pac200173122017.
Texte intégralRésumé :
Aluminium and ferric salts are widely used as coagulants in water and wastewater treatment. They are effective in removing a broad range of impurities from water, including colloidal particles and dissolved organic substances. Their mode of action is broadly understood in terms of essentially two mechanisms: charge neutralization of negatively charged colloids by cationic hydrolysis products and incorporation of impurities in an amorphous precipitate of metal hydroxide. The relative importance of these two mechanisms depends on many factors, especially pH and coagulant dosage. Alternative coagulants based on prehydrolyzed forms of aluminium or iron can be more effective than the traditional materials in many cases, but their mode of action is not completely understood, especially with regard to the role of charge neutralization and hydroxide precipitation. Basic principles of colloid stability and metal ion hydrolysis are briefly reviewed, and the action of hydrolyzing metal coagulants is then discussed, with some examples from recent experimental studies. Although it is possible to interpret results reasonably well in terms of established ideas, there are still some uncertainties that need to be resolved
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Riess, Jean G., et Marie Pierre Krafft. « Fluorocarbons and Fluorosurfactants for In Vivo Oxygen Transport (Blood Substitutes), Imaging, and Drug Delivery ». MRS Bulletin 24, no 5 (mai 1999) : 42–48. http://dx.doi.org/10.1557/s0883769400052313.
Texte intégralRésumé :
The development of biomaterials to treat, repair, or reconstruct the human body is an increasingly important component of materials research. Collaboration between materials researchers and their industrial and clinical partners is essential for the development of this complex field. To demonstrate the importance of these interactions, two articles in this issue focus on advances in biomaterials relating to the use of colloidal systems for transport, drug delivery, and other medical applications. These articles were coordinated by Dominique Muster (Université Louis Pasteur, Strasbourg) and Franz Burny (Hôpital Erasme, Brussels). The following is the first of these two articles.A large variety of colloidal Systems involving highly fluorinated components have been prepared and investigated in recent years. These fluorinated Systems comprise diverse ty pes of emulsions (e.g., direct, reverse, and multiple emulsions; microemulsions; gel emulsions; waterless emulsions) with a fluorocarbon phase (and often a fluorinated Surfactant), and a ränge of self-assemblies (vesicles, tubules, helices, ribbons, etc.) made from fluorinated amphiphiles. Fluorinated Langmuir films and fluorinated black lipid membranes (BLMs) also have been investigated.Research in this area was driven by the potential applications of such materials in medicine and biology. Fluorocarbon-based products are being developed as injectable oxygen carriers (“blood Substitutes”), media for liquid Ventilation, drug delivery Systems, and contrast agents for ultrasound imaging. One such agent has recently been approved for use in Europe and the United States. Several more products are in an advanced stage of clinical evaluation, and others are in various stages of preclinical development. From a more fundamental Standpoint, these materials are being investigated for assessing and understanding the impact that fluorinated components have on the formation, stability, structure, and properties of colloida l Systems in comparison with their hydrocarbon counterparts. The attention given to fluorinated colloids prompted the synthesis of numerous new families of fluorinated amphiphiles, which were to become components of such colloids.
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Puertas, A. M., et F. J. de las Nieves. « Colloidal Stability of Polymer Colloids with Variable Surface Charge ». Journal of Colloid and Interface Science 216, no 2 (août 1999) : 221–29. http://dx.doi.org/10.1006/jcis.1999.6294.
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Borgne, François Le, Michel Treuil, Jean-Louis Joron et Michel Lepiller. « Natural and EDTA-complexed lanthanides used as a geochemical probe for aquifers : a case study of Orleans valley’s alluvial and karstic aquifers ». Bulletin de la Société Géologique de France 176, no 6 (1 novembre 2005) : 513–29. http://dx.doi.org/10.2113/176.6.513.
Texte intégralRésumé :
Abstract The transit of chemical elements within the different parts of Orleans valley’s aquifer is studied by two complementary methods. Those methods rely on the fractionation of lanthanides (Ln) during their migration in natural waters. The first method consists in studying natural lanthanides patterns within the watershed, at its entries and exits. The second one lies on multi-tracer experiments with Ln-EDTA complexes. This work is completed through an observation network consisting of 52 piezometers set on a sand and gravel quarry, and the natural entries and exits of the aquifer. Orleans valley’s aquifer, which is made of an alluvial watershed lying on a karstic aquifer, is mainly fed by the Loire river via a large karstic network. At the entries of the aquifer (Loire river at Jargeau), the Ln concentrations in the dissolved fraction (< 0,22 μm) vary with the flow of the river. During floods, Loire river waters display bulk continental crust-like Ln compositions with a slight enrichment in heavy Ln from Dy to Lu. When the Loire river flow becomes low level, the crust-normalised Ln patterns show a depletion in light Ln whereas Lu concentrations remain identical. The same evolution spatially occurs between the entries and exits of the karstic network. Spring waters are depleted in light Ln relative to the Loire river whereas heavy Ln (Yb, Lu) remain constant during transit. Furthermore, the depletion in light Ln increases with the distance between entries and exits. Tracer experiments using EDTA-complexed Ln within and between the alluvial and calcareous parts of the watershed have shown that complexed Ln are fractionated across all these geological strata. The recoveries of tracers always follow the order light Ln < heavy Ln. Moreover, both sediments analyses and filtering experiments at a porosity of 0,02 μm show that, in the presence of EDTA, Ln adsorb onto sediments and colloids in the order light Ln > heavy Ln. On the other hand, the filtration of alluvial groundwater with high colloids content induces no significant Ln fractionation when the solution contains no strong chelating agent. Hence, the transit of natural and artificial Ln in Orleans valley aquifer can be explained by two complementary processes. (1) Decanting/filtering or, on the opposite, stirring of colloids. Those processes induce no important Ln fractionation. (2) Exchanges of Ln between solute complexes, colloids and sediments due to the presence of strong chelating agents. Those exchanges fractionate the Ln in the order of their stability constants. Considering the natural Ln fractionation that occurs in the Loire river and in the studied aquifer, the carbonates, the stability constants of which follow the order light Ln < heavy Ln, are the best candidates as natural strong chelating agents. From the hydrodynamic point of view, both tracer experiments and natural Ln concentrations show that the transfer of elements within the alluvial watershed is pulsed by the Loire river movements. During an ascent phase, the elements migrate away from and perpendicularly to the karstic channels direction. During the river descent, horizontal flows are quasi absent and migrations are mainly vertical from the alluvia down to the calcareous part of the aquifer. Due to those hydrodynamic characteristics, alluvia and non fissured limestone have a high dynamic confining capacity. Elements with high affinity for solid or colloidal phases (e.g. light Ln) have an increased confining capacity in the whole aquifer, by sorption and colloid filtration within the alluvia and at the alluvial-calcareous interface, and by colloid decanting within the karstic channels. Overall, this model combines two components. The first one, hydrodynamical, results from the repartition of the loads pulsed by river Loire through the karst. The second one physico-chemical, results from the element distribution mainly controlled by colloïde/solute complexes exchange coefficients.
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Astuti, Mikrajuddin Abdullah et Khairurrijal. « Synthesis of Luminescent Ink from Europium-Doped Y2O3 Dispersed in Polyvinyl Alcohol Solution ». Advances in OptoElectronics 2009 (8 juin 2009) : 1–8. http://dx.doi.org/10.1155/2009/918351.
Texte intégralRésumé :
Luminescent ink from europium-doped Y2O3 ( Y2O3:Eu) has been synthesized by two steps method: first, synthesis of luminescent powder of Y2O3:Eu by simple heating of metallic nitrates in a polymer solution and second, dispersing the powder in a polyvinyl alcohol (PVA) solution. The stability of the ink (luminescent colloid) was strongly affected by mixing process of the powder and the solution. Mixing process must be performed for a long time (about 8 hours) at above room temperature to product stable colloids. We observed that mixing at 30–40∘C resulted in a stable and highly dispersed colloid. The writing test was performed on a white paper to show the potential use of the colloid for making security codes.
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Licsko, I. « Coagulation mechanisms - nano- and microprocesses ». Water Science and Technology 50, no 12 (1 décembre 2004) : 193–200. http://dx.doi.org/10.2166/wst.2004.0713.
Texte intégralRésumé :
Possible coagulation mechanisms were studied in relatively high alkalinity model systems and surface waters. On the basis of available information, original laboratory experiments and simple calculation ere performed in order to show that the adsorption of Al3+ and Fe3+ ions is not the dominant process in decreasing the stability of suspended particles. The ions of the feeding coagulants hydrolyse within short time and form positively charged water soluble aluminium- or ferric hydroxides. Adsorption of these water soluble hydroxides onto the surface of colloids and quasi-colloid particles are restricted because of the quick completion of the hydrolysis process in relatively high alkalinity (>1.2 mmol/L) water. The result of complete hydrolysis of Al3+ or Fe3+ ions are slightly positively charged poorly water soluble aluminium or ferric hydroxide sols. The positively charged hydroxides and the associated water molecules are connected to each other by hydrogen bonds, providing a stabile structure. The hydrogen bonds provide the aggregation of slightly positively charged sol aggregation into flocs. Considering the repulsing forces among the sols, high numbers of individual sol particles (having nm sizes) are able adsorb onto the surface of suspended particles, changing their electrical charge and decreasing the stability of the colloids and quasi-colloid particles. This process is dominant in the destabilisation of suspended particles.
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Septiani, Devi Ayu, Jono Irawan, Hermansyah Hermansyah et Yayuk Andayani. « Microemulsion Stability of Virgin Coconut Oil Based on Tradition of Melala Sumbawa's Society ». Acta Chimica Asiana 4, no 2 (27 octobre 2021) : 120–26. http://dx.doi.org/10.29303/aca.v4i2.75.
Texte intégralRésumé :
The Melala is a tradition of the Sumbawa people who use coconut milk to obtain Sumbawa oil for traditional medicine. Coconut milk is a colloidal system of stable oil in water (O/W) microemulsion. Within a particular time, the emulsion will split to produce oil (VCO), protein, and water due to the colloid equilibrium on the stability of the coconut milk emulsion. The purpose of this study was to compare the microemulsion stability of the coconut milk colloid system. The VCO was isolated by heating, enzymatically, acidifying, and adding whiting methods for comparison. The physical stability of the O/W microemulsion was measured by the volume of VCO produced from various isolation methods in simple laboratory experiments. The results showed that the physical stability of the O/W microemulsion on VCO isolation by enzymatic method using papain enzyme was the least.
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Kabon, Barbara, Daniel I. Sessler et Andrea Kurz. « Effect of Intraoperative Goal-directed Balanced Crystalloid versus Colloid Administration on Major Postoperative Morbidity ». Anesthesiology 130, no 5 (1 mai 2019) : 728–44. http://dx.doi.org/10.1097/aln.0000000000002601.
Texte intégralRésumé :
Abstract Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Crystalloid solutions leave the circulation quickly, whereas colloids remain for hours, thus promoting hemodynamic stability. However, colloids are expensive and promote renal toxicity in critical care patients. This study tested the hypothesis that goal-directed colloid administration during elective abdominal surgery decreases 30-day major complications more than goal-directed crystalloid administration. Methods In this parallel-arm double-blinded multicenter randomized trial, adults having moderate- to high-risk open and laparoscopically assisted abdominal surgery with general anesthesia were randomly assigned to Doppler-guided intraoperative volume replacement with 6% hydroxyethyl starch 130/0.4 (n = 523) or lactated Ringer’s solution (n = 534). The primary outcome was a composite of serious postoperative cardiac, pulmonary, infectious, gastrointestinal, renal, and coagulation complications that were assessed with a generalized estimating equation multivariate model. The primary safety outcome was a change in serum creatinine concentration up to 6 months postoperatively, compared to baseline concentrations. Results A total of 1,057 patients were included in the analysis. Patients assigned to crystalloid received a median [quartile 1, quartile 3] amount of 3.2 l [2.3, 4.4] of crystalloid, and patients assigned to colloid received 1.0 l [0.5, 1.5] of colloid and 1.8 l [1.2, 2.4] of crystalloid. The estimated intention-to-treat common effect relative risk for the primary composite was 0.90 for colloids versus crystalloids (95% CI: 0.65 to 1.23, P = 0.51), and 18% (91 of 523) of colloid patients and 20% (103 of 534) of crystalloid patients incurred at least one component of the primary outcome composite. There was no evidence of renal toxicity at any time. Conclusions Doppler-guided intraoperative hydroxyethyl starch administration did not significantly reduce a composite of serious complications. However, there was also no indication of renal or other toxicity.
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Philipse, Albert P., et Diana Maas. « Magnetic Colloids from Magnetotactic Bacteria : Chain Formation and Colloidal Stability ». Langmuir 18, no 25 (décembre 2002) : 9977–84. http://dx.doi.org/10.1021/la0205811.
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Hidalgo-Álvarez, R., A. Martín, A. Fernández, D. Bastos, F. Martínez et F. J. de las Nieves. « Electrokinetic properties, colloidal stability and aggregation kinetics of polymer colloids ». Advances in Colloid and Interface Science 67 (septembre 1996) : 1–118. http://dx.doi.org/10.1016/0001-8686(96)00297-7.
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van Leeuwen, Y. M., K. P. Velikov et W. K. Kegel. « Colloidal stability and chemical reactivity of complex colloids containing Fe3+ ». Food Chemistry 155 (juillet 2014) : 161–66. http://dx.doi.org/10.1016/j.foodchem.2014.01.045.
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Ortega-Vinuesa, J. L., A. Martı́n-Rodrı́guez et R. Hidalgo-Álvarez. « Colloidal Stability of Polymer Colloids with Different Interfacial Properties : Mechanisms ». Journal of Colloid and Interface Science 184, no 1 (décembre 1996) : 259–67. http://dx.doi.org/10.1006/jcis.1996.0619.
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Varga, Zsigmond, Jennifer L. Hofmann et James W. Swan. « Modelling a hydrodynamic instability in freely settling colloidal gels ». Journal of Fluid Mechanics 856 (12 octobre 2018) : 1014–44. http://dx.doi.org/10.1017/jfm.2018.725.
Texte intégralRésumé :
Attractive colloidal dispersions, suspensions of fine particles which aggregate and frequently form a space-spanning elastic gel are ubiquitous materials in society with a wide range of applications. The colloidal networks in these materials can exist in a mode of free settling when the network weight exceeds its compressive yield stress. An equivalent state occurs when the network is held fixed in place and used as a filter through which the suspending fluid is pumped. In either scenario, hydrodynamic instabilities leading to loss of network integrity occur. Experimental observations have shown that the loss of integrity is associated with the formation of eroded channels, so-called streamers, through which the fluid flows rapidly. However, the dynamics of growth and subsequent mechanism of collapse remain poorly understood. Here, a phenomenological model is presented that describes dynamically the radial growth of a streamer due to erosion of the network by rapid fluid back flow. The model exhibits a finite-time blowup – the onset of catastrophic failure in the gel – due to activated breaking of the inter-colloid bonds. Brownian dynamics simulations of hydrodynamically interacting and settling colloids in dilute gels are employed to examine the initiation and propagation of this instability, which are in good agreement with the theory. The model dynamics is also shown to accurately replicate measurements of streamer growth in two different experimental systems. The predictive capabilities and future improvements of the model are discussed and a stability-state diagram is presented providing insight into engineering strategies for avoiding settling instabilities in networks meant to have long shelf lives.
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Peula-García, J. M., R. Hidalgo-Alvarez et F. J. de las Nieves. « Colloid stability and electrokinetic characterization of polymer colloids prepared by different methods ». Colloids and Surfaces A : Physicochemical and Engineering Aspects 127, no 1-3 (juillet 1997) : 19–24. http://dx.doi.org/10.1016/s0927-7757(96)03890-3.
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Ouali, L., J. François et E. Pefferkorn. « Adsorption of Telechelic Poly(ethylene oxide) on Colloids : Influence on Colloid Stability ». Journal of Colloid and Interface Science 215, no 1 (juillet 1999) : 36–42. http://dx.doi.org/10.1006/jcis.1999.6183.
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Aranyos, Tibor, Lajos Blaskó, Attila Tomócsik et Marianna Makádi. « The effect of compost application on physical properties of sandy soil ». Acta Agraria Debreceniensis, no 51 (10 février 2013) : 67–70. http://dx.doi.org/10.34101/actaagrar/51/2064.
Texte intégralRésumé :
The sewage sludge compost is suitable to improve the colloid-poor sandy soils, which are common characteristics of poor water- and nutrientholding capacity. The general characteristics of sandy soils are the light mechanical composition, the low content of humus and mineral colloids, large pore size and a bad aggregate stability. They have a poor nutrient supply capacity, due to its high porosity the organic matter is degraded very quickly to mineral colloids (Stefanovits et al., 1999).
By the compost application the soil is enriched mineral and organic colloids, thereby improving the soil structure. The effect of addition of compost to soil the water- and nutrient-holding capacity and porosity could be increased and the bulk density could be decreased (Martens and Frankenberger, 1992).
The aim of our experiment is to carry out physical measurements to determine the effects of compost treatment. In this study the results of the first year are presented.
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Tateno, Michio, Taiki Yanagishima et Hajime Tanaka. « Microscopic structural origin behind slowing down of colloidal phase separation approaching gelation ». Journal of Chemical Physics 156, no 8 (28 février 2022) : 084904. http://dx.doi.org/10.1063/5.0080403.
Texte intégralRésumé :
The gelation of colloidal particles interacting through a short-range attraction is widely recognized as a consequence of the dynamic arrest of phase separation into colloid-rich and solvent-rich phases. However, the microscopic origin behind the slowing down and dynamic arrest of phase separation remains elusive. In order to access microscopic structural changes through the entire process of gelation in a continuous fashion, we used core–shell fluorescent colloidal particles, laser scanning confocal microscopy, and a unique experimental protocol that allows us to initiate phase separation instantaneously and gently. Combining these enables us to track the trajectories of individual particles seamlessly during the whole phase-separation process from the early stage to the late arresting stage. We reveal that the enhancement of local packing and the resulting formation of locally stable rigid structures slow down the phase-separation process and arrest it to form a gel with an average coordination number of z = 6–7. This result supports a mechanical perspective on the dynamic arrest of sticky-sphere systems based on the microstructure, replacing conventional explanations based on the macroscopic vitrification of the colloid-rich phase. Our findings illuminate the microscopic mechanisms behind the dynamic arrest of colloidal phase separation, the emergence of mechanical rigidity, and the stability of colloidal gels.
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Tseng, Kuo-Hsiung, Yur-Shan Lin, Chaur-Yang Chang et Meng-Yun Chung. « A Study of a PID Controller Used in a Micro-Electrical Discharge Machining System to Prepare TiO2 Nanocolloids ». Nanomaterials 10, no 6 (29 mai 2020) : 1044. http://dx.doi.org/10.3390/nano10061044.
Texte intégralRésumé :
This study developed a micro-electrical discharge machining (micro-EDM) system for producing TiO2 nanocolloids. When a proportional–integral–derivative controller designed using the Ziegler–Nichols method was adopted to control the interelectrode gap, TiO2 nanocolloids were obtained from spark discharges generated between two titanium wires immersed in deionized water. For a pulse on time–off time of 40–40 μs and a colloid production time of 100 min, TiO2 nanocolloids were produced that had an absorbance of 1.511 at a wavelength of 245 nm and a ζ potential of −47.2 mV. They had an average particle diameter of 137.2 nm, and 64.2% of particles were smaller than 91.28 nm. The minimum particles were spherical. The characteristics of colloids confirmed that the micro-EDM system can produce TiO2 nanocolloids with excellent suspension stability. The colloid production method proposed in this study has the advantages of low equipment cost and no dust diffusion in the process environment. These advantages can improve the competitiveness of the electric spark discharge method for high-quality TiO2 nanoparticle production. The colloids produced in this study did not contain elements other than titanium and oxygen, and they may prevent secondary environmental pollution.
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F, Czechowski. « Colloidal Stability of Bitumens Related to their Generic Composition ». Petroleum & ; Petrochemical Engineering Journal 6, no 4 (20 octobre 2022) : 1–9. http://dx.doi.org/10.23880/ppej-16000322.
Texte intégralRésumé :
Three bitumens obtained from crude oils widely differing in chemical nature were analyzed for generic composition. Separation into group components was carried out by liquid chromatography, using a new procedure. With this method, five fractions were separated, i.e. saturates, cyclics, light resins, heavy resins and asphaltenes. The size distribution of the asphaltene particles in the bitumens and the Heithaus parameters characterizing the colloidal stability of bitumen were determined. The results suggest that the role of the light resins in bitumen differs from that of the heavy resins, as they are constituents of the dispersing and dispersed phase, respectively. The cyclic components and light resins form the dispersing medium of bitumen while the heavy resins and asphaltenes constitute the dispersed material. Saturates are the bitumen components that deteriorate the peptization of asphaltene particles.
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Bastos, D., et F. J. de las Nieves. « Colloidal stability of sulfonated polystyrene model colloids. Correlation with electrokinetic data ». Colloid and Polymer Science 272, no 5 (mai 1994) : 592–97. http://dx.doi.org/10.1007/bf00653226.
Texte intégral
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ZABULONOV, Yu L., V. M. KADOSHNIKOV, T. I. MELNYCHENKO, H. P. ZADVERNYUK, S. V. KUZENKO et Yu V. LYTVYNENKO. « Geochemical Behavior of Ferric Hydroxide Nanodispersion Under the Influence of Weak Magnetic Fields ». Mineralogical journal 43, no 2 (2021) : 74–79. http://dx.doi.org/10.15407/mineraljournal.43.02.074.
Texte intégralRésumé :
The change of geochemical properties of ferric hydroxide nanoparticles under the influence of a weak magnetic field was investigated. Ferric hydroxide nanoparticles formed as a result of the interaction of iron-containing minerals with natural aqueous solutions are of importance for geochemical processes, especially hypergenesis, sedimentation, and soil formation. The hydrolysis of ferric chloride in hot water (t = 70-75°С) was used to obtain ferric hydroxide nanoparticles under laboratory conditions. The nanodispersion (colloidal solution) was exposed to a weak pulsed magnetic field. The spectrophotometric properties of the colloidal solution of ferric hydroxide were determined using an SF-46 spectrophotometer in the wavelength range of 320-610 nm. The size of colloidal particles was calculated by a method based on the theory of Rayleigh light scattering. The size of colloidal particles depended on the exposure duration of a pulsed magnetic field on the colloidal solution. The size of colloidal particles was due to a change in the magnitude of the diffuse ionic atmosphere under the influence of a pulsed magnetic field. The kinetic stability of the colloidal solution was evaluated by the coagulation threshold, which was determined visually by the appearance of the turbidity of ferric hydroxide colloid when adding NaCl solution. The kinetic stability of a colloidal system was determined by the size of colloidal particles. These results can be used to better understand certain hypergenesis, sedimentation, and soil formation processes.
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Basina, Georgia, Hafsa Khurshid, Nikolaos Tzitzios, George Hadjipanayis et Vasileios Tzitzios. « Facile Organometallic Synthesis of Fe-Based Nanomaterials by Hot Injection Reaction ». Nanomaterials 11, no 5 (28 avril 2021) : 1141. http://dx.doi.org/10.3390/nano11051141.
Texte intégralRésumé :
Fe-based colloids with a core/shell structure consisting of metallic iron and iron oxide were synthesized by a facile hot injection reaction of iron pentacarbonyl in a multi-surfactant mixture. The size of the colloidal particles was affected by the reaction temperature and the results demonstrated that their stability against complete oxidation related to their size. The crystal structure and the morphology were identified by powder X-ray diffraction and transmission electron microscopy, while the magnetic properties were studied at room temperature with a vibrating sample magnetometer. The injection temperature plays a very crucial role and higher temperatures enhance the stability and the resistance against oxidation. For the case of injection at 315 °C, the nanoparticles had around a 10 nm mean diameter and revealed 132 emu/g. Remarkably, a stable dispersion was created due to the colloids’ surface functionalization in a nonpolar solvent.
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Thar, Aung Chan, Thaung Hlaing Win, Nyein Wint Lwin et Than Zaw Oo. « Scrutiny of Surface Plasmon Resonance Bands of Colloidal Cu and Cu-Ag Nanoparticles in Different Reaction Media for Stability Evaluation ». Journal of Nano Research 52 (mai 2018) : 115–21. http://dx.doi.org/10.4028/www.scientific.net/jnanor.52.115.
Texte intégralRésumé :
The copper nanoparticles (CuNPs) were developed in two different reaction media (distilled water (DW) and ethylene glycol (EG)) by chemical reduction method using two different stabilizers (polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP)). We carried out a careful examination of the time evolution of surface plasmon resonance (SPR) bands (specifically, peak positions and intensities) of colloidal CuNPs so as to evaluate their stability. In addition, the changing pattern of SPR peak positions and intensities during the stability time period was also investigated. Effects of stabilizer materials, stabilizer concentration, Ag capping and reaction medium on the stability of CuNPs colloids have been highlighted. The maximum stability of CuNPs is 4 hours with stabilizer PEG and is 4 days with PVP in DW. They, with PVP, extend up to 10 days in the different reaction medium (EG). The stability time of CuNPs in EG is further lengthened to 20 days in the presence of Ag capping (Cucore AgshellNPs). Thus a proper selection of the stabilizing/capping agent and the reaction medium is critical in determining the stability of CuNPs colloids. The benefits of stabilization of CuNPs for real world applications are immense and this study would help in examinning the stability of other novel plasmonic metal nanostructures.
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Shiyan, Ludmila N., Ksenia I. Machekhina, Elena A. Tropina, Elena N. Gryaznova et Vladimir V. An. « Effect of Humic Substances and Silicon Ions on Stability of Iron Hydroxide (III) Nanoparticles ». Advanced Materials Research 872 (décembre 2013) : 237–40. http://dx.doi.org/10.4028/www.scientific.net/amr.872.237.
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The paper reports on experimental modeling of the colloid system composition in natural groundwater. It is shown that the stability of iron hydroxide nanoparticles relates to the presence of silica and humic substances. It was found out the molar ratio of iron/silicon/organic substance is equal to 1/7/2, where stable iron (III) hydroxide nanoparticles form. The iron hydroxide nanoparticle size ranging from 30 to 600 nm was determined. It characterizes the steady state of the colloidal system.
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Waggett, Franceska, Mohamad Shafiq et Paul Bartlett. « Failure of Debye-Hückel Screening in Low-Charge Colloidal Suspensions ». Colloids and Interfaces 2, no 4 (22 octobre 2018) : 51. http://dx.doi.org/10.3390/colloids2040051.
Texte intégralRésumé :
Derjaguin–Landau–Verwey–Overbeek (DLVO) theory remains the cornerstone of colloid stability. Electrostatic interactions dominate van der Waals attractions at large colloid-colloid separations h, unless strongly screened. Under these conditions, the potential U ( h ) between charged colloids is expected to be exponentially screened, U ( h ) ∼ exp ( − κ h ) / h , with κ − 1 = λ D where λ D is the classical Debye-Hückel screening length. By measuring the force between individual charged particles at dilute electrolyte concentrations (<mM) using optical tweezers, we tested experimentally the prediction κ − 1 = λ D in a nonpolar solvent. At low salt concentrations, we found close agreement between the directly-measured decay length κ − 1 and Debye-Hückel predictions. However, above a critical electrolyte concentration (≈450 μ M), we obtained significant discrepancies between measured and predicted screening lengths, with κ − 1 ≫ λ D . In marked contrast to expectations, we found that the measured screening length κ − 1 appears to grow as the ionic strength of the solution is increased. The origin of this discrepancy is discussed and the importance of considering the surface is highlighted.