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Träfflista för sökning "WFRF:(Abbas Zareen 1962) "

Sökning: WFRF:(Abbas Zareen 1962)

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1.
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2.
  • Abbas, Zareen, 1962, et al. (författare)
  • Activity Coefficients of Concentrated Salt Solutions: A Monte Carlo Investigation
  • 2019
  • Ingår i: Journal of Solution Chemistry. - : Springer Science and Business Media LLC. - 0095-9782 .- 1572-8927. ; 48:8-9, s. 1222-1243
  • Tidskriftsartikel (refereegranskat)abstract
    • Monte Carlo (MC) simulations were used to calculate single ion and mean ionic activity coefficients and water activity in concentrated electrolytes and at elevated temperatures. By using a concentration dependent dielectric constant, the applicability range of the MC method was extended to 3mol·L−1 or beyond, depending on the salt. The calculated activity coefficients were fitted to experimental data by adjusting only one parameter, i.e., the cation radius. Fitted ionic radii obtained by such a procedure indicate the extent of cation–anion interaction in a salt solution. For example, the fitted radii of Li+ and Na+ in LiClO3 and NaClO3 indicate that Li+ is strongly hydrated and has a weak interaction with the ClO3− ion whereas Na+ forms ion pairs and loses its hydration. The single ion activity coefficients for protons and chloride ions in HCl were calculated by MC simulations and compared with experimental values obtained by ion selective electrodes. The calculated single ion activity coefficients for protons and chloride ions are much lower and higher, respectively, than the experimental values. However, the mean activity coefficients of HCl obtained by the MC simulations, ion selective electrodes and vapor pressure measurements are in good agreement. In the case of NaCl and KCl the calculated single ion activity coefficients of Na+, K+, and Cl− are much closer to the values obtained by ion selective electrodes. The results in HCl indicate that the hydrated proton is large and includes the chloride ion within the hydration shell, i.e., the apparent size of the chloride ion is negligible.
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3.
  • Abbas, Zareen, 1962, et al. (författare)
  • From restricted towards realistic models of salt solutions: Corrected Debye–Hückel theory and Monte Carlo simulations
  • 2007
  • Ingår i: Journal of Mathematical Fluid Mechanics. - : Elsevier BV. - 1422-6952 .- 1422-6928 .- 0378-3812. ; 260:2, s. 233-247
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of bulk salt solutions over wide concentration ranges are explored by a combination of simple physical theory and Monte Carlo (MC) simulations. The corrected Debye–Hückel (CDH) theory which incorporates ion size effects in a linear response approximation is extended to yield free energy and other thermodynamic properties by integration of the chemical potential over concentration. Charging integration which is usually used to obtain an electrostatic contribution of total free energy of electrolytes is avoided in this new direct approach. MC simulations are performed with a modified Widom particle insertion method, which also provides directly the ionic activity coefficients. The validity of the CDH theory is tested by comparison with the MC simulation data for 1:1, 2:1, 2:2 and 3:1 restricted primitive model (RPM) electrolytes over a wide concentration range and at various ion sizes. Mean ionic activity and osmotic coefficients calculated by the CDH theory in RPM approximation of electrolyte are fitted to experimental data by adjusting only a mean ionic diameter. Good fits up to 1 molal (m) concentration are obtained for a large number of salt solutions. MC simulations data for unrestricted primitive model (UPM) of 1:1 and 2:1 electrolytes are also fitted to the experimental data by varying the cation radius while keeping the anion radius fixed at a crystallographic value. The success of this approach is found to be salt specific. For example good fits up to 2 and 3.5 m concentrations were obtained for LiCl and LiBr, respectively. However in the case of less dissociated salts such as NaCl and KI the experimental data could only be fitted up to one molal concentration. Possibility of extending the applicability range of the CDH theory to concentrations >2 m is explored by including a concentration dependent dielectric constant as measured in experiments. Mean ionic activity coefficients for a number of salts could successfully be fitted up to 3 m concentration by adjusting only a mean ionic diameter. Difficulties encountered in simultaneously fitting the mean ionic activity and osmotic coefficients at salt concentrations >2 m are discussed.
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4.
  • Abbas, Zareen, 1962, et al. (författare)
  • Monte Carlo simulation of the dissociation constants of CO2 in 0 to 1 molal sodium chloride between 0 and 25 °C
  • 2013
  • Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 150:1, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • Stoichiometric dissociation constants of the carbon dioxide system in NaCl solution between 0 and 1 mol and 0 to 25 °C were estimated by Monte Carlo (MC) simulations, and compared with Pitzer calculations and experimental measurements. The MC simulations used experimentally determined dielectric constants of water at different temperatures, and optimal agreement with the experimental data and Pitzer calculations was achieved by adjusting the ionic radii. This simple procedure resulted in effective ionic radii which were further used to simulate the activity coefficients of salt mixtures. The first and second stoichiometric dissociation constants of carbonic acid in NaCl solution (pK1⁎ and pK2⁎) were estimated from the MC-derived activity coefficients of mixed salts in NaCl. The MC results are in good agreement with the experimental data as well as with the Pitzer calculations. This study shows that Monte Carlo simulations in the temperature and ionic strength range relevant to seawater can provide pK values of the same quality as Pitzer calculations, and constitutes the first step in developing a temperature-dependent MC model for seawater. While MC calculations require greater computing resources, the number of parameters derived by fitting to thermodynamic data is substantially smaller than for Pitzer calculations.
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5.
  • Abbas, Zareen, 1962, et al. (författare)
  • Monte Carlo Simulations of Salt Solutions: Exploring the Validity of Primitive Models
  • 2009
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:17, s. 5905-5916
  • Tidskriftsartikel (refereegranskat)abstract
    • An extensive series of Monte Carlo (MC) simulations were performed in order to explore the validity of simple primitive models of electrolyte solutions and in particular the effect of ion size asymmetry on the bulk thermodynamic properties of real salt solutions. Ionic activity and osmotic coefficients were calculated for 1:1, 2:1, and 3:1 electrolytes by using the unrestricted primitive model (UPM); i.e., ions are considered as charged hard spheres of different sizes dissolved in a dielectric continuum. Mean ionic activity and osmotic coefficients calculated by the MC simulations were fitted simultaneously to the experimental data by adjusting only the cation radius while keeping the anion radius fixed at its crystallographic value. Ionic radii were further optimized by systematically varying the cation and anion radii at a fixed sum of ionic radii. The success of this approach is found to be highly salt specific. For example, experimental data (mean ionic activity and osmotic coefficients) of salts which are usually considered as dissociated such as HCl, HBr, LiCl, LiBr, LiClO4, and KOH were successfully fitted up to 1.9, 2.5, 1.9, 3, 2.5, and 4.5 M concentrations, respectively. In the case of partially dissociated salts such as NaCl, the successful fits were only obtained in a more restricted concentration range. Consistent sets of the best fitted cation radii were obtained for acids, alkali, and alkaline earth halides. A list of recommended ionic radii is also provided. The reliability of the optimized ionic radii was further tested in simulations of the osmotic coefficients of LiCl−NaCl−KCl salt mixtures. A very good agreement between the simulated and experimental data was obtained up to ionic strength of 4.5 M.
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6.
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7.
  • Abbas, Zareen, 1962, et al. (författare)
  • Size-Dependent Surface Charging of Nanoparticles
  • 2008
  • Ingår i: J of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:15, s. 5715-5723
  • Tidskriftsartikel (refereegranskat)abstract
    • Experimental interest in the possible curvature dependence of particle charging in electrolyte solutions is subjected to theoretical analysis. The corrected Debye-Hückel theory of surface complexation (CDH-SC) and Monte Carlo (MC) simulation are applied to investigate the dependence of surface charging of metal oxide nanoparticles on their size. Surface charge density versus pH curves for spherical metal oxide nanoparticles in the size range of 1-100 nm are calculated at various concentrations of a background electrolyte. The surface charge density of a nanoparticle is found to be highly size-dependent. As the particle diameter drops to below 10 nm there is considerable increase in the surface charge density as compared with the limiting values seen for particles larger than 20 nm. This increase in the surface charge density is due to the enhanced screening efficiency of the electrolyte solution around small nanoparticles, which is most prominent for particles of diameters less than 5 nm. For example, the surface charge densities calculated for 2 nm particles at 0.1 M concentration are very close to the values obtained for 100 nm particles at 1 M concentration. These predictions of the dependence of surface charge density on particle size by the CDH-SC theory are in very good agreement with the corresponding results obtained by the MC simulations. A shift in the pH value of the point of zero charge toward higher pH values is also seen with a decreasing particle size.
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8.
  • Abbas, Zareen, 1962, et al. (författare)
  • Synthesis, characterization and particle size distribution of TiO2 colloidal nanoparticles
  • 2011
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 384:1-3, s. 254-261
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanoparticles of controlled size, well defined shape, pure phase and of clean surfaces are ideal model systems to investigate surface/interfacial reactions. In this study we have explored the possibility of synthesizing TiO2 nanoparticles in the size range of 7–20 nm under well controlled experimental conditions. A simple method based on the hydrolysis of TiCl4 was used to obtain particles having surfaces free from organics. Stable dispersions of TiO2 nanoparticles of various sizes were obtained by optimizing the reaction/dialysis time and temperature. The synthesized TiO2 particles were found to be predominantly of anatase phase and narrow particle size distributions were obtained. The TiO2 particles were characterized with respect to their phase, size and shape by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Particle size distribution in a colloidal dispersion was obtained by the electrospray scanning mobility particle sizer (ES-SMPS) method and compared with an average particle size determined from dynamic light scattering (DLS). The average particle sizes obtained by the DLS and ES-SMPS methods were in good agreement, while a primary particle size of 4 nm was found in X-ray diffraction irrespective of the particle size in solution. Early stages of the nucleation process were monitored by the ES-SMPS method. These results show that small particles of 4–5 nm are initially formed and it is highly likely that large particles are formed due to aggregation of primary particles.
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9.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • A study of the accelerated ageing process of cementitious materials
  • 2011
  • Ingår i: Advances in Construction Materials through Science and Engineering. ; RILEM PRO 79
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents part of a study in a research project called “Ageing of the cementitious materials for storage of nuclear waste”. The goal is to establish a mechanistic model for predicting longevity of concrete in storage facilities for nuclear waste. As deposition of low and intermediate level radioactive waste (LILW) needs up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Laboratory methods are, therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. Chemical and electrochemical acceleration approaches were tried in this study. Chemical acceleration involves leaching of samples under conditions of actual groundwater. Electrochemical migration is also applied to accelerate leaching process. Chemical and XRD analysis is carried out to identify the compositions before and after the acceleration tests. The results indicate a possibility to produce aged specimens for further mechanical tests and other physical tests, such as porosity and diffusivity.
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10.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Ageing of cementitious materials for storage of nuclear waste
  • 2011
  • Ingår i: Nordic Concrete Research. ; Publication No. 43, s. 429-432
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents an on-going research project dealing with ageing process of cementitious materials in a perspective of hundreds and thousands years. As it is risky to use empirical models for extrapolation of performance data from relatively short term experiments, a mechanism-based (chemo-mechanical coupled) model for safer prediction of longevity of concrete in storage facilities for nuclear waste is needed. The project work involves thermodynamic modeling, development of accelerated aging tests, physical, chemical and mineralogical characterization of young and aged cementitious materials, including mechanical, transport (diffusivity) properties, binding (adsorption) capacities and surface complexation (charging) behavior.
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11.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Ageing process of cementitious materials: Ion transport and diffusion coefficient
  • 2012
  • Ingår i: Concrete Repair, Rehabilitation and Retrofitting III - Proceedings of the 3rd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2012. - 9780415899529 ; , s. 369-374
  • Konferensbidrag (refereegranskat)abstract
    • Risk assessment analysis concerning service life predictions of concrete structures in nuclear waste repositories requires broad knowledge about long-term concrete deterioration processes. It is well known that the degradation process of cementitious materials involves diffusion of internal and external ions, interaction between these ions and re-deposition of the interacted products. However, although diffusion properties play an important role in the deterioration process, there is a lack of reliable data on ion diffusivity in concrete, especially co-existing ions rather than chloride. The aim of this study is to further analyze multi-component ionic diffusion accompanied with surface complexation and selective adsorption. Natural diffusion cell and field immersion tests are used to analyze transport properties of ions present in groundwater surrounding nuclear waste repositories such as chloride, sodium, lithium and calcium ions, through cement paste. Analytical techniques such as Ion chromatography, potentiometric titration, inductively coupled plasma mass spectrometry and X-ray fluorescence methods are used. Results indicate that the ionic diffusion coefficients differ between different ions and the higher the concentration of the ions, the lower the diffusion coefficient will be.
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12.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Chloride Penetration Resistance of Calcium Depleted Concrete Specimens
  • 2014
  • Ingår i: Proceedings of XXII Nordic Concrete Research Symposium, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 487-490
  • Konferensbidrag (refereegranskat)abstract
    • To facilitate the service life predictions regarding durability of nuclear waste repositories acceleration methods enhancing the decalcification process are used. However, in order to reach an efficient leaching rate small sample sizes have been used which limits further testing. In this study an electro-chemical migration method to accelerate leaching of calcium from concrete specimens of size 50×100Ø is presented. Rapid chloride migration test is utilized to account for the changes in chloride diffusion coefficient of concrete specimens due to calcium depletion. The results indicate up to at least 70% of increase of chloride diffusion coefficient as a result of decalcification.
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13.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Development of an electro-chemical accelerated ageing method for leaching of calcium from cementitious materials
  • 2016
  • Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 705-718
  • Tidskriftsartikel (refereegranskat)abstract
    • To facilitate the long term durability predictions of nuclear waste repositories, acceleration methods enhancing calcium leaching process from cementitious materials are needed, even though mechanisms not necessarily comparable to those predominant in a natural leaching process may be developed. In the previously published acceleration methods the samples are very small, which limits further physical or mechanical tests. In this paper, a new acceleration method based on electro-chemical migration is presented. The method although not driven with the same kinetics as in natural leaching, was designed in such a way that unnecessarily destructive by-effects could be minimized while promoting a higher leaching rate for a sample size suitable for further testing the mechanical and physical properties. It is shown that approximately 1x10^6 C of electrical charge per paste specimen of size Ø50 x 75 mm (approximately 230 g) is required to leach out the total amount of Portlandite. The chemical and mineralogical properties of leached samples are characterized by various techniques. It is concluded that aged samples are comparable to those leached in a natural leaching process as both are characterized by a layered system comprising an unaltered core delineated by total dissolution of Portlandite followed by a progressive decalcification of the calcium silicate hydrate gel.
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14.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Electrochemical migration technique to accelerate ageing of cementitious materials
  • 2013
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759810468 ; 56
  • Konferensbidrag (refereegranskat)abstract
    • Durability assessment of concrete structures for constructions in nuclear waste repositories requires long term service life predictions. As deposition of low and intermediate level radioactive waste (LILW) takes up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Using acceleration methods producing aged specimens would decrease the need of extrapolating short term data sets. Laboratory methods are therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. This paper presents an electro-chemical migration method to increase the rate of calcium leaching from cementitious specimens. This method is developed based on the fact that major long term deterioration process of hardened cement paste in concrete structures for deposition of LILW is due to slow diffusion of calcium ions. In this method the cementitious specimen is placed in an electrochemical cell as a porous path way through which ions can migrate at a rate far higher than diffusion process. The electrical field is applied to the cell in a way to accelerate the ion migration without making destructions in the specimen's micro and macroscopic properties. The anolyte and catholyte solutions are designed favoring dissolution of calcium hydroxide and compensating for the leached calcium ions with another ion like lithium.
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15.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Mineralogical, Physical and Chemical Characterization of Cementitious Materials Subjected to Accelerated Decalcification by an Electro-Chemical Method
  • 2014
  • Ingår i: Nordic Concrete Research. - 0800-6377. ; 1/2014:49, s. 181-198
  • Tidskriftsartikel (refereegranskat)abstract
    • To facilitate the service life predictions regarding durability of nuclear waste repositories acceleration methods enhancing the decalcification process are needed. In this study an electro-chemical migration method to accelerate leaching of calcium from cementitious specimens of sizes 50×100Ø and 75×50Ø mm is presented. The mineralogical, physical and chemical properties of degraded samples are characterized. The results demonstrate that up to 70% decrease in strength, 50 % decrease in E-modulus, 90 % increase in gas permeability, at least 70% increase in chloride diffusion coefficient and 70 % increase in pore volume could be expected due to leaching of portlandite from concrete.
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16.
  • Babaahmadi, Arezou, 1985, et al. (författare)
  • Physical and Mechanical Properties of Cementitious Specimens Exposed to an Electrochemically Derived Accelerated Leaching of Calcium
  • 2015
  • Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 1976-0485 .- 2234-1315. ; 9:3, s. 295-306
  • Tidskriftsartikel (refereegranskat)abstract
    • Simulating natural leaching process for cementitious materials is essential to perform long-term safety assessments of repositories for nuclear waste. However, the current test methods in literature are time consuming, limited to crushed material and often produce small size samples which are not suitable for further testing. This paper presents the results from the study of the physical (gas permeability as well as chloride diffusion coefficient) and mechanical properties (tensile and compressive strength and elastic modulus) of solid cementitious specimens which have been depleted in calcium by the use of a newly developed method for accelerated calcium leaching of solid specimens of flexible size. The results show that up to 4 times increase in capillary water absorption, 10 times higher gas permeability and at least 3 times higher chloride diffusion rate, is expected due to complete leaching of the Portlandite. This coincides with a 70 % decrease in mechanical strength and more than 40 % decrease in elastic modulus.
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17.
  • Balitskii, O. A., et al. (författare)
  • Aqueous processable WO3-x nanocrystals with solution tunable localized surface plasmon resonance
  • 2016
  • Ingår i: Rsc Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:64, s. 59050-59054
  • Tidskriftsartikel (refereegranskat)abstract
    • Heavily doped tungsten oxide nanoparticles with localized surface plasmon resonances (LSPRs) were recently highlighted as potential substitutes for noble metals in the field of plasmonic applications. Herein, oxygen deficient, spherically shaped WO3-x nanocrystals (NCs) were synthesized with a pronounced visible LSPR absorbance peak instead of a broadband tail usually observed for WO3-x nanowires. Although the tuning of the plasmon resonances was achieved mainly by changing the nanocrystals composition or solvent refraction index, we demonstrate this via the interfacial charge donation/extraction. In an aqueous NCs dispersion, the LSPR peak was either blue shifted in an acidic solution up to 80 nm or bleached by a basic solution making the NCs appropriate for sensing applications.
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18.
  • Brown, Matthew A, et al. (författare)
  • Measure of Surface Potential at the Aqueous-Oxide Nanoparticle Interface by XPS from a Liquid Microjet
  • 2013
  • Ingår i: Nano letters. - 1530-6984 .- 1530-6992. ; 13:11, s. 5403-5407
  • Tidskriftsartikel (refereegranskat)abstract
    • We show that the surface potential at a water–oxide nanoparticle (NP) interface, long considered an immeasurable direct quantity, can be measured by X-ray photoelectron spectroscopy (XPS) from a liquid microjet. This new method does not require a priori knowledge of the particles’ surface structure or of the ion distribution throughout the electrical double layer for its interpretation and can be applied to any colloidal suspension independent of composition, particle size and shape, and solvent. We demonstrate the application for aqueous suspensions of 9 nm colloidal silica (SiO2) at pH 0.3 and 10.0, where the surface potential changes from positive to negative. The experimental results are compared with calculated surface potentials based on Guoy–Chapman theory and are shown to be in good agreement.
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19.
  • Brown, Matthew, et al. (författare)
  • Determination of Surface Potential and Electrical Double-Layer Structure at the Aqueous Electrolyte-Nanoparticle Interface
  • 2016
  • Ingår i: Physical Review X. - 2160-3308. ; 6:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The structure of the electrical double layer has been debated for well over a century, since it mediates colloidal interactions, regulates surface structure, controls reactivity, sets capacitance, and represents the central element of electrochemical supercapacitors. The surface potential of such surfaces generally exceeds the electrokinetic potential, often substantially. Traditionally, a Stern layer of nonspecifically adsorbed ions has been invoked to rationalize the difference between these two potentials; however, the inability to directly measure the surface potential of dispersed systems has rendered quantitative measurements of the Stern layer potential, and other quantities associated with the outer Helmholtz plane, impossible. Here, we use x-ray photoelectron spectroscopy from a liquid microjet to measure the absolute surface potentials of silica nanoparticles dispersed in aqueous electrolytes. We quantitatively determine the impact of specific cations (Li + , Na + , K + , and Cs + ) in chloride electrolytes on the surface potential, the location of the shear plane, and the capacitance of the Stern layer. We find that the magnitude of the surface potential increases linearly with the hydrated-cation radius. Interpreting our data using the simplest assumptions and most straightforward understanding of Gouy-Chapman-Stern theory reveals a Stern layer whose thickness corresponds to a single layer of water molecules hydrating the silica surface, plus the radius of the hydrated cation. These results subject electrical double-layer theories to direct and falsifiable tests to reveal a physically intuitive and quantitatively verified picture of the Stern layer that is consistent across multiple electrolytes and solution conditions.
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20.
  • Brown, Matthew, et al. (författare)
  • Effect of Electrolyte Concentration on the Stern Layer Thickness at a Charged Interface
  • 2016
  • Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1521-3773 .- 1433-7851. ; 55:11, s. 3790-3794
  • Tidskriftsartikel (refereegranskat)abstract
    • The chemistry and physics of charged interfaces is regulated by the structure of the electrical double layer (EDL). Herein we quantify the average thickness of the Stern layer at the silica (SiO2) nanoparticle/aqueous electrolyte interface as a function of NaCl concentration following direct measurement of the nanoparticles’ surface potential by X-ray photoelectron spectroscopy (XPS). We find the Stern layer compresses (becomes thinner) as the electrolyte concentration is increased. This finding provides a simple and intuitive picture of the EDL that explains the concurrent increase in surface charge density, but decrease in surface and zeta potentials, as the electrolyte concentration is increased.
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21.
  • Brown, Matthew, et al. (författare)
  • Effect of Surface Charge Density on the Affinity of Oxide Nanoparticles for the Vapor–Water Interface
  • 2013
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:16, s. 5023-5029
  • Tidskriftsartikel (refereegranskat)abstract
    • Using in-situ X-ray photoelectron spectroscopy at the vapor–water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye–Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si–O–) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor–water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye–Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.
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22.
  • Cronstrand, Peter, 1965, et al. (författare)
  • Electrochemical leaching of cementitious materials: an experimental and theoretical study
  • 2011
  • Ingår i: Procedings of the 1st International Symposium on Cement-Based Materials for Nuclear Wastes, NUMCEM 2011. ; Session 3:Paper O344
  • Konferensbidrag (refereegranskat)abstract
    • The acceleration of aging processes using forced ionic migration has been studied from a combined theoretical and experimental point of view. The preliminary results indicate that only a fraction of the reactive-transport through the sample is associated with dissolution of portlandite and the subsequent release of calcium. Further experimental work is needed in order to characterize the sample in terms of mineral composition and microstructure and to verify the modeling approach.
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23.
  • Danielsson, Karin, et al. (författare)
  • Effects of the adsorption of NOM model molecules on the aggregation of TiO2 nanoparticles in aqueous suspensions
  • 2018
  • Ingår i: NanoImpact. - : Elsevier BV. - 2452-0748. ; 10, s. 177-187
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2018 Interaction of synthetic TiO2(anatase) nanoparticles in aqueous suspension at pH 5 was investigated as a function of time in the presence of various organic molecules in terms of adsorption and aggregation behaviour. ζ-potential and average particle diameter were determined with electrophoretic and dynamic light scattering, respectively, while batch adsorption experiments were used to quantify the amount of organic ligand adsorbed to the TiO2NP. An IR spectroscopic study was carried out at pH 2.8 and 5 to gain information about the interactions of the adsorbed molecules with the TiO2surface on the molecular level. Furthermore, DLVO calculations provided information about the interaction energies between particles and their tendency to aggregate under some experimental conditions. Colloidal stability of TiO2NPs in the presence of organic molecules was studied during a time period of up to 90 days. Results showed that ligands with different functional groups may interact differently with the surface depending on the type and position of available surface sites, the molecular structure of the ligand and suspension pH. Adsorption, hydrodynamic diameter and ζ-potential were affected by the ligand concentration in all tested systems. Increased concentration gave rise to increased adsorption, while ζ-potential decreased and charge inversion was observed for all tested molecules at pH 5. IR spectroscopic study showed the formation of inner sphere and/or outer sphere complexes depending on pH and type of organic ligand. According to DLVO calculations, the critical coagulation concentration (CCC) indicated a trend of increasing colloidal stability with increased concentration of SRFA at pH 5, which was in agreement with the experimental data.
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24.
  • Fang, Zhao, 1986, et al. (författare)
  • TiO2 nanoparticle interactions with supported lipid membranes – an example of removal of membrane patches
  • 2016
  • Ingår i: RSC Advances. - 2046-2069. ; 6:94, s. 91102-91110
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a need for different levels of model systems for effect studies of engineered nanoparticles and the development of nanoparticle structure–activity relationships in biological systems. Descriptors for nanoparticles based on their interactions in molecular model systems may become useful to predict toxicological responses of the nanoparticles in cells. Towards this end, we report on nanoparticle-induced formation of holes in supported model membranes. Specifically, TiO2 nanoparticle – lipid membrane interactions were studied under low ionic strength, basic conditions (pH 8), using different membrane compositions and several surface-sensitive analytical techniques. It was found that for mixed POPC/POPG (PG fractions ≥ 35%) membranes on silica supports, under conditions where electrostatic repulsion was expected, the addition of TiO2 nanoparticles resulted in transient interaction curves, consistent with the removal of part of the lipid membrane. The formation of holes was inferred from quartz crystal microbalance with dissipation (QCM-D) monitoring, as well as from optical measurements by reflectometry, and also verified by atomic force microscopy (AFM) imaging. The interaction between the TiO2 nanoparticles and the PG-containing membranes was dependent on the presence of Ca2+ ions. A mechanism is suggested where TiO2 nanoparticles act as scavengers of Ca2+ ions associated with the supported membrane, leading to weakening of the interaction between the membrane and the support and subsequent removal of lipid mass as TiO2 nanoparticles spontaneously leave the surface. This mechanism is consistent with the observed formation of holes in the supported lipid membranes.
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25.
  • Gunnarsson, Magnus, et al. (författare)
  • Corrected Debye-Hückel analysis of surface complexation; III. Spherical particle charging including ion condensation.
  • 2004
  • Ingår i: Journal of colloid and interface science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 274:2, s. 563-78
  • Tidskriftsartikel (refereegranskat)abstract
    • Statistical mechanics has been used to derive a model for the charging of a spherical particle in a salt solution to complement our experimental studies and gain a deeper understanding of the processes involved in surface complexation. Our chosen model goes beyond the equilibrium constants and the Gouy-Chapmann theory currently used in surface complexation models. The proton adsorption is taken to occur at a harmonic potential well on the surface characterized by a frequency v and a well depth u(0). Outside the particle surface there is a capacitor layer of width w(c) which is impenetrable to the salt ions. The diffuse screening of the charged particle is described by a corrected Debye-Hückel analysis accounting for ion size in the ion-ion interactions. To account also for nonlinear electrostatic response a layer of condensed counterions has been introduced. The criterion for the onset of ion condensation is that the electrostatic field exceeds a linear response criterion. Ion size effects are accounted for in terms of hole-corrected electrostatic energies and excluded volume. The model has been applied to titrated surface charge data on goethite (alpha-FeOOH) at various background concentrations and good agreement between the experimental data and the model was obtained. Both the size of the screening ions and the central particle size were shown to be of importance for the surface charge.
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26.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • Molecular dynamics simulation of nanocolloidal amorphous silica particles : Part I.
  • 2007
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:22, s. 224711-
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit molecular dynamics simulations were applied to a pair of amorphous silica nanoparticles in aqueous solution, with diameter of 4.4 nm and with four different background electrolyte concentrations, to extract the mean force acting between the two silica nanoparticles. Dependences of the interparticle forces on the separation and the background electrolyte concentration were demonstrated. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated. A "patchy" double layer of adsorbed sodium counterions was observed. Dependences of the interparticle potential of mean force on the separation and the background electrolyte concentration were demonstrated. Direct evidence of the solvation forces is presented in terms of changes of the water ordering at the surfaces of the isolated and double nanoparticles. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was investigated in terms of quantifying the effects of the number of water molecules separately inside each pair of nanoparticles by defining an impermeability measure. A direct correlation was found between the impermeability (related to the silica surface "hairiness") and the disruption of water ordering. Differences in the impermeability between the two nanoparticles are attributed to differences in the calculated electric dipole moment.
  •  
27.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • Molecular dynamics simulation of nanocolloidal amorphous silica particles: Part III
  • 2009
  • Ingår i: The Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit-solvent molecular dynamics simulations were applied to four pairs of amorphous silica nanoparticles, two pairs having a diameter of 2.0 nm and two pairs with diameter 3.2 nm. The silica nanoparticles were immersed in a background electrolyte consisting of Ca2+ and Cl− ions and water and mean forces acting between the pair of silica nanoparticles were extracted at four different background electrolyte concentrations. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. Dependence of the interparticle potential of mean force on the center-of-mass separation and the silicon to sodium ratio (5:1 and 20:1) is demonstrated. A Si:Na+ ratio of 5:1 gave more repulsive interparticle potentials and lower numbers of internanoparticle or “bridging” hydrogen bonds. Conversely a Si:Na+ ratio of 20:1 yielded more attractive potentials and higher numbers of bridging hydrogen bonds. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was also investigated. The effect of the sodium double layer on water ordering was observed. The number of water molecules trapped inside the nanoparticles was investigated, and at the highest background ionic concentrations were found to consistently behave in accordance with there being an osmotic pressure. This study highlights the effect of divalent (Ca2+) background ions on the interparticle potentials compared with previous work using monovalent (Na+) background ions. Mechanisms of coagulation and the stability of silica nanocolloids found from this work appear to be in agreement with findings from experiments described in the literature.
  •  
28.
  • Jenkins, Samantha, 1967-, et al. (författare)
  • Molecular dynamics simulations of nanocolloidal amorphous silica particles: Part II
  • 2008
  • Ingår i: The Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:16
  • Tidskriftsartikel (refereegranskat)abstract
    • Explicit molecular dynamics simulations were applied to a pair of amorphous silica nanoparticles with diameter of 3.2 nm immersed in a background electrolyte. Mean forces acting between the pair of silica nanoparticles were extracted at four different background electrolyte concentrations. The dependence of the interparticle potential of mean force on the separation and the silicon to sodium ratio, as well as on the background electrolyte concentration, are demonstrated. The pH was indirectly accounted for via the ratio of silicon to sodium used in the simulations. The nature of the interaction of the counterions with charged silica surface sites (deprotonated silanols) was also investigated. The effect of the sodium double layer on the water ordering was investigated for three Si:Na+ ratios. The number of water molecules trapped inside the nanoparticles was investigated as the Si:Na+ ratio was varied. Differences in this number between the two nanoparticles in the simulations are attributed to differences in the calculated electric dipole moment. The implications of the form of the potentials for aggregation are also discussed.
  •  
29.
  • Johnsson, Ann-Catrin J. H., 1981, et al. (författare)
  • Aggregation of Nanosized Colloidal Silica in the Presence of Various Alkali Cations Investigated by the Electrospray Technique
  • 2008
  • Ingår i: Langmuir. ; 24:22
  • Tidskriftsartikel (refereegranskat)abstract
    • The slow aggregation process of a concentrated silica dispersion (Bindzil 40/220) in the presence of alkali chlorides (LiCl, NaCl, KCl, RbCl, and CsCl) was investigated by means of mobility measurements. At intervals during the aggregation, particles and aggregates were transferred from the liquid phase to the gas phase via electrospray (ES) and subsequently size selected and counted using a scanning mobility particle sizer (SMPS). This method enables the acquisition of particle and aggregate size distributions with a time resolution of minutes. To our knowledge, this is the first time that the method has been applied to study the process of colloidal aggregation. The obtained results indicate that, independent of the type of counterion, a sufficient dilution of the formed gel will cause the particles to redisperse. Hence, the silica particles are, at least initially, reversibly aggregated. The reversibility of the aggregation indicates additional non-DLVO repulsive steric interactions that are likely due to the presence of a gel layer at the surface. The size of the disintegrating aggregates was monitored as a function of the time after dilution. It was found that the most stable aggregates were formed by the ions that adsorb most strongly on the particle surface. This attractive effect was ascribed to an ion−ion correlation interaction.
  •  
30.
  • Johnsson, Ann-Catrin J. H., 1981, et al. (författare)
  • Combined Electrospray-Scanning Mobility Particle Sizer (ES-SMPS) and Time-Resolved Synchrotron Radiation-Small-Angle X-ray Scattering (SR-SAXS) Investigation of Colloidal Silica Aggregation. Part II. Influence of Aggregation Initiator on Gel Stability
  • 2011
  • Ingår i: Journal of Physical Chemistry B. ; 115:31, s. 9547-9555
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of ion specificity on the slow aggregation of silica nanoparticles with various initial morphology was investigated with an electrospray-scanning mobility particle sizer (ES-SMPS) and time-resolved synchrotron radiation-small-angle X-ray scattering (SR-SAXS). This combination provides a unique tool to monitor and resolve the early aggregate development in detail. Aggregation was induced by varying the K2CO3 or KCl concentration to obtain a fixed gelation time of 40 min, and the results were compared with those obtained in a previous paper (Johnsson et al. J. Phys. Chem. B2011, 115, 765–775) for NaCl. All dispersions produced gels that contained free primary particles well past the point of gelation (PoG). The initial aggregate formation and obtained gel morphologies were independent of the aggregation initiator. Nevertheless, ion-specific effects were observed for the rate of the stability increase of the 3-dimensional (3D) gel structure. The formation of a stable structure was fastest in the presence of the strongly hydrated counterions, and a clear anion effect was observed. The obtained gel stabilities were interpreted by relating the rate of formation of covalent siloxane bonds to the polarization of the water molecules surrounding structure-maker ions.
  •  
31.
  • Johnsson, Ann-Catrin J. H., 1981, et al. (författare)
  • Combined Electrospray-SMPS and SR-SAXS Investigation
  • 2011
  • Ingår i: The Journal of Physical Chemistry B. ; 115:5, s. 765-775
  • Tidskriftsartikel (refereegranskat)abstract
    • The slow aggregation of monodisperse, polydisperse, and preaggregated silica nanoparticles was studied with an electrospray−scanning mobility particle sizer (ES-SMPS) and time-resolved synchrotron radiation−small-angle X-ray scattering (SR-SAXS). Aggregation was induced by varying the NaCl concentration to obtain a fixed gelation time of 40 min. The combination of these techniques provides a unique tool to monitor and resolve the aggregate development in detail. The monodisperse spherical particles were converted to dimers, trimers, and eventually larger clusters as the aggregation proceeded, while the polydisperse spherical particles formed large clusters at an early stage. The initial particle shape and polydispersity had profound effects on the morphology of the aggregates; spherical primary particles produced compact spherical clusters, whereas the preaggregated dispersions formed open, elongated aggregates. All dispersions produced gels that contained free primary particles well past the point of gelation. The stability of the aggregates and the gel morphology were interpreted by relating to the structure of porous gel layers around the particles.
  •  
32.
  •  
33.
  • Karlsson, Mikael, 1978, et al. (författare)
  • Characterisation of silicon, zirconium and aluminium coated titanium dioxide pigments recovered from paint waste
  • 2019
  • Ingår i: Dyes and Pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 162, s. 145-152
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2018 Elsevier Ltd Titanium dioxide (TiO2) is the major white pigment used by the paint industry. However, the production of TiO2is associated with a high carbon footprint. An alternative source of pigment could be created by developing a method to recover it from waste paint. In this paper two rutile pigments with different surface treatments were recovered from paint by a thermal recycling process. The pigments were analysed using powder x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface area measurements (BET), laser diffraction for particle size analysis and zeta potential measurements before and after the recycling process. It was concluded that the rutile cores of both pigments were intact and there were no major changes in particle size distribution or surface charge for either pigment induced by the recycling process. However, XPS and zeta potential measurements showed that the surface coating of the pigments can be more or less degraded depending on the chemical nature, which might imply the need for further re-coating after-treatment. Another option would be to find another application for the pigment where the quality and function of the coating is of less importance.
  •  
34.
  • Karlsson, Mikael, 1978, et al. (författare)
  • Surface properties of recycled titanium oxide recovered from paint waste
  • 2018
  • Ingår i: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 125, s. 279-286
  • Tidskriftsartikel (refereegranskat)abstract
    • Aluminium oxide coated rutile pigment was extracted from a paint matrix by means of a thermal recycling process. The objective was to investigate the effect of the recycling process on the surface properties of the pigment. The pigment was analysed using powder x-ray diffraction (XRD), surface area measurements (BET), laser diffraction for particle size analysis and X-ray photoelectron spectroscopy (XPS) before and after the recycling process. Investigations on the zeta potential and the surface charge were performed as well. It was concluded that the rutile crystalline core and the aluminium oxide coating of the pigment were still intact after the recycling process. The particle size distribution of the recycled pigment was slightly broader compared to the virgin pigment. The measured magnitude in zeta potential of the recycled pigment was lower than for the virgin pigment. This difference is thought to be caused by alteration in the surface hydroxyl concentration. Surface charge titrations showed differences between the virgin and the recycled pigment at alkaline pH and at low salt concentrations.
  •  
35.
  • Kolman, Krzysztof, et al. (författare)
  • Molecular dynamics exploration for the adsorption of benzoic acid derivatives on charged silica surfaces
  • 2019
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 578
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2019 Elsevier B.V. Molecular dynamics (MD) simulations provide molecular level information about the interaction of organic molecules with the solid surfaces. There has been much development of this method to simulate the interaction of organic molecules with neutral surfaces but relatively less information is available regarding the interactions with charged surfaces. In this study we have developed MD model for the charged silica surface and have investigated the interactions of different benzoic acid derivatives with the charged silica surface in pure and saline water at acidic, neutral and basic pH. The investigated molecules were 2,3-dihydroxybenzoic acid (23DHBA), 3,4-dihydroxybenzoic acid (34DHBA), 1,2,4-benzenetricarboxylic acid (BTCA) and phthalic acid (PHTHA). To simplify the analysis of results, three different simulation systems were considered. Clustering simulations showed how molecules aggregate in solution, pulling simulations provided quantitate information regarding the interactions of single molecule with the silica surface, whereas adsorption simulations focused on the adsorption of multiple molecules on the surface. In general, at pH 2–3, all investigated molecules were clustering and were attracted towards the surface. At pH 7, due to arising electrostatic repulsion, the interactions became weaker which prevented 23DHBA, 34DHBA and BTCA from clustering, however, they continued to adsorb on the silica surface. The adsorption of 23DHBA and 34DHBA decreased significantly at pH 9–10 due to electrostatic repulsion between the molecules and charged silica surface, while BTCA adsorbed slightly stronger due to interactions with ions close to the surface. PHTHA molecules behaved differently by clustering stronger and adsorbing weaker at higher pH. The results of MD simulations presented in this work by using pulling and adsorption approaches provide possibility to compare the results with experimental data.
  •  
36.
  • Kumar, Sonal, et al. (författare)
  • A Bi-based artificial interphase to achieve ultra-long cycling life of Al-metal anode in non-aqueous electrolyte
  • 2024
  • Ingår i: Energy Storage Materials. - 2405-8297. ; 65
  • Tidskriftsartikel (refereegranskat)abstract
    • Rechargeable aluminum-ion batteries (RAB) with Al-metal anode are regarded as cost-effective and environmentally sustainable energy storage systems. However, tapping the high volumetric capacity of the Al-anode has been a challenge because of the spontaneous and irreversible formation of the oxide layer on its surface that renders it electrochemically inactive. Though recently reported AlCl3-based electrolytes overcome this problem by breaking down this oxide layer, their highly corrosive nature hampers commercialization. Here, we investigate a novel approach to protect the Al-anode from severe oxidation by engineering an artificial protective interphase. A unique and less corrosive combination of Al(CF3SO3)3 salt and BiCl3 additive reacts with the Al-anode intrinsically to form an inorganic-rich protective bilayer. This layer is electronically insulating and significantly reduces the charge transfer resistance and surface activation energy at the anode, enabling plating/stripping at extremely low overpotential of <0.1 V that can be sustained for record-long cycling times of >4000 h.
  •  
37.
  • Lohcharoenkal, Warangkana, et al. (författare)
  • Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines
  • 2021
  • Ingår i: Biosensors. - : MDPI AG. - 0956-5663 .- 2079-6374. ; 11:10
  • Forskningsöversikt (refereegranskat)abstract
    • Cytokines are a large group of small proteins secreted by immune and non-immune cells in response to external stimuli. Much attention has been given to the application of cytokines’ detection in early disease diagnosis/monitoring and therapeutic response assessment. To date, a wide range of assays are available for cytokines detection. However, in specific applications, multiplexed or continuous measurements of cytokines with wearable biosensing devices are highly desirable. For such efforts, various nanomaterials have been extensively investigated due to their extraordinary properties, such as high surface area and controllable particle size and shape, which leads to their tunable optical emission, electrical, and magnetic properties. Different types of nanomaterials such as noble metal, metal oxide, and carbon nanoparticles have been explored for various biosensing applications. Advances in nanomaterial synthesis and device development have led to significant progress in pushing the limit of cytokine detection. This article reviews currently used methods for cytokines detection and new nanotechnology-based biosensors for ultrasensitive cytokine detection
  •  
38.
  • Nayeri, Moheb, 1979, et al. (författare)
  • Measurements of screening length in salt solutions by total internal reflection microscopy: Influence of van der Waals forces and instrumental noise
  • 2013
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 429, s. 74-81
  • Tidskriftsartikel (refereegranskat)abstract
    • Total internal reflection microscopy (TIRM) measurements of colloidal spheres in aqueous electrolyte solutions have been carried out with focus on screening properties of various electrolytes and methods and analyses for reliably extracting them from TIRM measurements. Approximations based on Lifshitz theory of flat plates are found to yield van der Waals interactions that are too strong compared to measured interaction potentials. Allowing for some attenuation of these interactions due to surface roughness, a consistent set of screening lengths can be extracted by fitting a model of the interaction, comprising screened Coulomb, van der Waals, and gravitational interactions, to the TIRM data. With the exception of the 2:2 electrolytes, the screening lengths extracted from the TIRM measurements are well described by Debye–Hückel theory, including some surfactants below their critical micelle concentration and electrolytes with large size asymmetries between anion and cation. In 2:2 electrolytes the screening lengths are found to be larger than the corresponding Debye length by as much as 50% at the highest salt concentrations studied. While this deviation is significantly larger than predictions of theory based on the primitive model of electrolytes, similar magnitudes are found from analysis of BD simulations with added noise at realistic levels in the incident intensity. The work shows that care has to be taken when extracting parameters governing potentials in the presence of noise, particularly at high ionic strengths when potentials become steep at short separations.
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39.
  • Nordholm, Sture, 1944, et al. (författare)
  • Generalized van der Waals Theory of Molecular Fluids in Bulk and at Surfaces
  • 2018
  • Bok (övrigt vetenskapligt/konstnärligt)abstract
    • Generalized van der Waals Theory of Molecular Fluids in Bulk and at Surfaces presents successful research on the development of a new density theory of fluids that makes it possible to understand and predict a wide range of properties and phenomena. The book brings together recent advances relating to the Generalized van der Waals Theory and its use in fluid property calculations. The mathematics presentation is oriented to an audience of varying backgrounds, and readers will find exercises that can be used as a textbook for a course at the upper undergraduate or graduate level in physics or chemistry. In addition, it is ideal for scientists from other areas, such as geophysics, oceanography and molecular biology who are interested in learning about, and understanding, molecular fluids. Key Features •Presents an approximate, but fully derived and physically explained, theory of molecular fluids to facilitate broad applications •Derives a density functional theory of classical fluids and applies it to obtain equations of state, as well as non-uniform fluid properties, e.g., surface tension and adsorption •Demonstrates how the theory can be applied to complex multi-center molecules forming a polymer fluid •Provides user-friendly programs to redraw figures for variable parameters and to perform calculations in particular applications •Includes a set of exercises to support use of the book in a course Readership Researchers in statistical mechanics, scientists and engineers working with fluids as well as graduate and upper undergraduate students in chemistry, chemical engineering and physics
  •  
40.
  • Perez-Holmberg, Jenny, 1977, et al. (författare)
  • Near Room Temperature Synthesis of Monodisperse TiO2 Nanoparticles: Growth Mechanism
  • 2013
  • Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:10, s. 5453-5461
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrolysis of TiCl4 was used to form monodisperse nanoparticles of TiO2 with clean surfaces. The solid fraction and solution composition during synthesis were simulated using equilibrium data, and formation and growth was followed with two complementary techniques, an electrospray-scanning mobility particle sizer (ES-SMPS) and dynamic light scattering (DLS). In ES-SMPS the number density of particles is measured. Droplets formed in the spraying step mainly contain electrolyte, giving rise to residue particles that are detected together with the nanoparticles of interest. Discrimination between the two kinds of particles can be made by changing the flow conditions and applicability of the method for in situ measurements of particle size during growth is demonstrated. In DLS the hydrodynamic mobility is measured, and further insight into the initial growth mechanism was revealed by observation of slow, sustained oscillations in the scattered intensity, indicating a dissolution–precipitation mechanism at the lowest pH values. The size of the particles formed in the dissolution–precipitation step is most likely determined by the surface charge, and larger particles are formed by aggregation.
  •  
41.
  • Perez-Holmberg, Jenny, 1977, et al. (författare)
  • Nonlinear Concentration Dependence of the Collective Diffusion Coefficient of TiO2 Nanoparticle Dispersions
  • 2011
  • Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115, s. 13609-13616
  • Tidskriftsartikel (refereegranskat)abstract
    • Aqueous dispersions of titania nanoparticles are shown to yield collective diffusion coefficients in dynamic light-scattering measurements that depend nonlinearly on particle concentration under dilute conditions. From theory, one expects a linear dependence for monodisperse systems except for strongly interacting charged particles in low ionic strength media. Angularly resolved dynamic light-scattering measurements reveal that aggregates are present, which explains the collective diffusion coefficient tending to lower values in the dilute limit than the Stokes Einstein diffusion coefficient of the nanoparticles. A simple theoretical model based on mixtures of charged nanoparticle spheres and small amounts of larger-sized neutral or weakly charged spheres, modeling the presence of aggregates, is applied and shown to yield predictions in qualitative accord with the experimental trends. In particular, the downward curvature of the collective diffusion coefficient on diluting the system arises in the model from nanoparticles being driven into close proximity to the larger particles by electrostatic interactions. Similar experimental trends observed in silica dispersions suggest that the behavior is not an isolated finding. This study clearly shows that a small number of larger aggregates dramatically change the measured value of the collective diffusion coefficient; thus, care must be exercised when characterizing nanoparticles with dynamic light scattering.
  •  
42.
  • Perez-Holmberg, Jenny, 1977, et al. (författare)
  • Surface charge and interfacial potential of titanium dioxide nanoparticles: Experimental and theoretical investigations
  • 2013
  • Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 407:1, s. 168-176
  • Tidskriftsartikel (refereegranskat)abstract
    • Size dependent surface charging and interfacial potential of titanium dioxide (TiO2) nanoparticles are investigated by experimental and theoretical methods. Commercially available TiO2 (P25) nanoparticles were used for surface charge determinations by potentiometric titrations. Anatase particles, 10 and 22 nm in diameter, were synthesized by controlled hydrolysis of TiCl4, and electrophoretic mobilities were determined at a fixed pH but at increasing salt concentrations. Corrected Debye–Hückel theory of surface complexation (CDH-SC) was modified to model the size dependent surface charging behavior of TiO2 nanoparticles. Experimentally determined surface charge densities of rutile and P25 nanoparticles in different electrolytes were accurately modeled by the CDH-SC theory. Stern layer capacitances calculated by the CDH-SC theory were in good agreement with the values found by the classical surface complexation approach, and the interaction of protons with OH groups is found to be less exothermic than for iron oxide surfaces. Moreover, the CDH-SC theory predicts that the surface charge density of TiO2 nanoparticles of diameter <10 nm is considerably higher than for larger particles, and pH at the point of zero charge (pHPZC) shifts to higher pH values as the particle size decreases. The importance of including the particle size in calculating the zeta potentials from mobilities is demonstrated. Smoluchowski theory showed that 10 nm particles had lower zeta potential than 22 nm particles, whereas a reverse trend was seen when zeta potentials were calculated by Ohshima’s theory in which particle size is included. Electrokinetic charge densities calculated from zeta potentials were found to be only one third of the true surface charge densities.
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43.
  • Quiñones, A. O., et al. (författare)
  • Influence of concentration and temperature dependent dielectric constants on the thermodynamics of electrolytes
  • 2023
  • Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 371
  • Tidskriftsartikel (refereegranskat)abstract
    • The symmetric Poisson–Boltzmann theory, the modified Poisson–Boltzmann theory, and the mean spherical approximation are utilized to calculate the osmotic coefficient, and the individual and mean activity coefficients of model KCl, LiCl, NaCl, and NaClO4 electrolytes all dissociated in water where the dielectric constant depends on concentration. The theories are also employed to compute the same thermodynamic quantities for HCl and NaCl solutions where the dielectric constant is now temperature dependent. In each situation the theoretical predictions are compared with the corresponding exact benchmark Monte Carlo simulation results. The mean spherical approximation and the modified Poisson–Boltzmann theory reproduce the simulation data for osmotic coefficient quantitatively and that for the mean activity almost quantitatively. The individual activities are accurately represented by the modified Poisson–Boltzmann theory but only qualitatively by the symmetric Poisson–Boltzmann and the mean spherical approximation. In general, the symmetric Poisson–Boltzmann theory shows good agreement with the simulations at low concentrations but deviates at higher concentrations.
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44.
  • Rama, Prasad, et al. (författare)
  • Interfacial interactions of humic acids with polystyrene nano-plastics in aqueous/ionic environments: a molecular dynamics exploration
  • 2023
  • Ingår i: Environmental Science-Nano. - : Royal Society of Chemistry (RSC). - 2051-8153 .- 2051-8161. ; 10:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Plastics pose a serious threat to both marine and freshwater life after being discarded and broken down into smaller particles such as micro and nano-plastic particles. The nano-sized plastic particles are small enough in size and similar to surfaces of biological molecules, thereby potentially altering the intra-cellular interactions and their biological fate. In order to increase our understanding of the interactions among the molecules of natural organic matter and carboxylate functionalized polystyrene nano-plastics, we have performed a modelling study of the aquatic environment at different pH conditions using molecular dynamics (MD) simulations at an atomistic scale. Humic acids (HAs) are the most common constituents of natural organic matter, usually found in soil, water, and its sediments. As a proxy for humic acids, we have used Temple-Northeastern-Birmingham (TNB), an equivalent molecule to HA in its composition. We show that TNB molecules exhibit strong interactions with polystyrene (PS) nano-plastic particles at pH-4 but weak interaction at pH-7, whereas moderate interaction at pH-9 both in fresh and saltwater. The interaction between carboxylated polystyrene particles and TNB molecules is found to be counter-ion mediated and is enhanced in the presence of saltwater, i.e., at 0.5 M NaCl electrolyte. An enhanced condensation of Na+ counter-ions onto the surface of nano-plastics brings more water molecules to its interface, hence, enriching the hydrophilicity of nano-plastics. An ordered network structure of water molecules has also been observed at the interface of the PS-slab with an increase in pH of the aquatic environment, leading to a preferential alignment of water molecules, resulting in a strong hydration layer. This strong hydration layer also keeps the TNB molecules away from the vicinity of the PS-slab interface. The surface potential trends obtained from the MD simulations are in agreement with the measured zeta potential values showing that the surface charge density of PS nano-plastics increases with an increase in the pH of aquatic solutions. Hence, our simulations provide molecular-level insights into the phenomenon associated with the adsorption/accumulation of molecules of natural organic matter towards the nano-plastics and are helpful in understanding the formation of eco-corona on plastic nanoparticles.
  •  
45.
  • Rama, Prasad, et al. (författare)
  • The influence of silica nanoparticle geometry on the interfacial interactions of organic molecules: a molecular dynamics study
  • 2022
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24, s. 3713-3721
  • Tidskriftsartikel (refereegranskat)abstract
    • The role of nanoparticle shape in the interaction and adsorption of organic molecules on the particle surface is an unexplored area. On the other hand, such knowledge is not only vital for a basic understanding of organic molecule interaction with nanoparticle surfaces but also essential for evaluating the cellular uptake of nanoparticles for living organisms. The current study investigates the role of silica nanoparticle shape in the interactions of phthalic acid organic molecules by using molecular dynamics simulations. Silica nanoparticles of two different geometries namely spheroid and cuboid with varying charge densities along with protonated and deprotonated phthalic acid molecules are studied. The adsorption characteristics of phthalic acid molecules on these nanoparticles have been analysed under different aquatic environments. The interactions of phthalic acid molecules, water molecules and ions were found to be different for spheroid and cubic shaped particles at pH values of 2-3, 7 and 9-10. The interaction of phthalic acid molecules with cubical silica nanoparticles is enhanced compared to the spherical shape particles. Such an enhanced interaction was seen when the silica surface is neutral, pH 2-3 and when the silica surface is charged at pH 7 and pH 9-10 in the presence of 0.5 M NaCl electrolyte. The cuboid-shaped silica also exhibited more hydrophilicity and less negative surface potential compared to spheroid shaped particles at pH 9-10. This is due to the enhanced condensation of Na+ counter-ions at the cuboid nanoparticle solution interface as to the interface of spheroid particles, which is well in agreement with Manning's theory of counter-ion condensation. Simulation results presented in this study indicate that the shape of the silica nanoparticle has significant influence on the interaction of water molecules, counter-ions and organic molecules which consequently determine the adsorption behaviour of organic molecules on the nanoparticle surface.
  •  
46.
  • Redondo, A. B., et al. (författare)
  • Nanoparticle-Induced Charge Redistribution of the Air-Water Interface
  • 2015
  • Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:5, s. 2661-2668
  • Tidskriftsartikel (refereegranskat)abstract
    • The airwater interface is believed to carry a negative electrostatic potential that is nontrivial to invert through pH, electrolyte, or electrolyte strength. Here, through a combined experimental and theoretical study, we show that the close approach of a negatively charged nanoparticle induces a charge redistribution of the airwater interface. Using different electrolytes to control the interfacial potential of the nanoparticles, X-ray photoelectron spectroscopy (XPS) results establish that nanoparticles with a more negative zeta potential adsorb closer to the airwater interface than do the same particles with a less negative zeta potential. The short-ranged attractive force between two (nominally) negative surfaces is caused by charge redistribution under the strong electric field of the nanoparticle that locally inverts the charge density of the airwater interface from negative to positive. The nature of the nanoparticles counterions modulates the attractive interaction, which thus could be used to control reactivity, stability, and nanoparticle self-assembly at airwater interfaces.
  •  
47.
  • Simonsson, Isabelle, 1990, et al. (författare)
  • Experimental investigations into the irregular synthesis of iron(iii) terephthalate metal-organic frameworks MOF-235 and MIL-101 dagger
  • 2021
  • Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 50, s. 4976-4985
  • Tidskriftsartikel (refereegranskat)abstract
    • MOF-235(Fe) and MIL-101(Fe) are two well-studied metal-organic frameworks (MOFs) with dissimilar crystal structures and topologies. Previously reported syntheses of the former show that it has greatly varying surface areas, indicating a lack of phase purity of the products, i.e. the possible presence of both MOFs in the same sample. To find the reason for this, we have tested and modified the commonly used synthesis protocol of MOF-235(Fe), where a 3 : 5 molar ratio of iron(iii) ions and a terephthalic acid linker is heated in a 1 : 1 DMF : ethanol solvent at 80 degrees C for 24 h. Using XRD and BET surface area (SA(BET)) measurements, we found that it is difficult to obtain a pure phase of MOF-235, as MIL-101 also appears to form during the solvothermal treatment. Comparison of the XRD peak height ratios of the synthesis products revealed a direct correlation between the MOF-235/MIL-101 content and surface area; more MOF-235 yields a lower surface area and vice versa. In general, using a larger (3 : 1) DMF : ethanol ratio than that reported in the literature and a stoichiometric (4 : 3) Fe(iii) : TPA ratio yields a nearly pure MOF-235 product (SA(BET) = 295 m(2) g(-1), 67% yield). An optimized synthesis procedure was developed to obtain high-surface area MIL-101(Fe) (SA(BET) > 2400 m(2) g(-1)) in a large yield and at a previously unreported temperature (80 degrees C vs. previously used 110-150 degrees C). In situ X-ray scattering was utilized to investigate the crystallization of MOF-235 and MIL-101. At 80 degrees C, only MOF-235 formed and at 85 and 90 degrees C, only MIL-101 formed.
  •  
48.
  • Simonsson, Isabelle, 1990, et al. (författare)
  • The specific co-ion effect on gelling and surface charging of silica nanoparticles: Speculation or reality?
  • 2018
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 559, s. 334-341
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2018 Elsevier B.V. Based on extensive experimental investigations on many different oxide nanoparticles, it is now a well-established view that the counter-ions exhibit ion specific effects due to their high charge density and strong interaction with oppositively charged surfaces. On the other hand, studies regarding co-ion effects are scarcely reported in the literature. In this study we have measured the surface charge densities and gel-times of silica nanoparticles in a number of salts which have the same counter-ions but different co-ions, i.e. anions in this case. Gel-times were measured in LiCl, NaCl, NaNO3, NaClO4, NaClO3and Na2SO4as well as in KCl, KNO3, and K2SO4. We have seen clear correlations between the gel-times and the extent of ion pairing in the solutions; salts that have strong ion pairing exhibit longer gel-times than salts having highly dissociated ions. To better understand the mechanisms at work we have determined the surface charging of silica nanoparticles in these salt solutions and we have observed that the surface charging behavior of silica nanoparticles follows the trends seen in the gel-time studies. From our gel-time determinations and potentiometric measurements we can claim that there is a clear co-ion effect on the gelling and surface charging of silica nanoparticles.
  •  
49.
  • Sögaard, Christian, 1990, et al. (författare)
  • Development and Evaluation of Polyether Ether Ketone (PEEK) Capillary for Electrospray
  • 2019
  • Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:1, s. 1151-1156
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2019 American Chemical Society. With the rapid development of nanotechnology, there is urgent need of characterizing techniques; especially determining the particle size distribution directly from solution. Dynamic light scattering is often used but presence of a small number of aggregates can greatly influence the size distribution. Electrospray scanning mobility particle sizer (ES-SMPS) is rapidly emerging as an alternative method in colloidal science. However, a major limitation is the use of silica-coated capillaries, which are negatively charged at pH > 3, and therefore making its use difficult for positively charged nanoparticles. In this work, we have developed the polyether ether ketone (PEEK) capillary for ES-SMPS, which removes this limitation because it carries no charge. We have shown that the new capillary not only produced equally good particle size distributions for negatively charged particles (SiO2, Au, and latex) as obtained with silica capillaries, but also precise particle size distributions for positively charged particles (TiO2). Moreover, the PEEK capillaries are much cheaper than the silica capillaries. Thus, the results shown in this paper strengthen the development of the ES-SMPS method as a versatile method for determining the particle size distributions of colloidal sols directly from solution.
  •  
50.
  • Sögaard, Christian, 1990, et al. (författare)
  • Hofmeister effects in the gelling of silica nanoparticles in mixed salt solutions
  • 2021
  • Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 611
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the nature of specific interaction of ions with the charged silica nanoparticles is vital not only to produce gels for applications such as grouting but also for determining their long term stability. Interaction of silica nanoparticles in single salt solutions has been thoroughly investigated but in mixed salt solutions is rarely investigated. In this work we have investigated the gelling of silica nanoparticles in the mixtures of monovalent ions as well as in the mixtures of divalent and monovalent ions. To gain an understanding of the interaction of ions with the charged silica surface at molecular level we have performed molecular dynamics (MD) simulations. Our overall goal was to find out if in salt mixtures ions silica interactions follow the Hofmeister series or not and how ion specific interactions may change when chaotropic ions are successively replaced by kosmotropic or vice versa. The gelling results show that generally monvalent ions in salt mixtures follow the Hofmeister series, e.g., the gel times in the mixtures of lithium and sodium chlorides are much longer than in the mixtures of lithium and potassium chlorides. On the other hand, gel times in the salt mixtures containing divalent ions do not follow the expected Hofmeister series e.g. mixtures of magnesium and sodium chlorides show shorter gel times than that of calcium and sodium chlorides. However, pH dependent gelling revealed that at pH values less than 9 gelling in these mixtures follow the normal Hofmeister series i.e., longer gelling time in magnesium and sodium chlorides than in calcium and sodium chlorides. This reversal of Hofmeister series for divalent and monovalent salt mixtures at pH > 9 and normal Hofmeister series at pH < 9 is reported for the first time in literature. Such a revesal at pH> 9 is explained due to enhanced surface charge, ordring of surface water layer which leads to enhanced ion specificity of strongly hydrated ions such as Mg2+. Moreover, in mixtures having the same divalent salt but different monovalent salts such as magnesium chlorides mixtures with lithium, sodium and potassium chlorides a normal Hofmeister series prevails. MD simulations results revealed that Mg2+ ions retain their strong hydration shell while interacting with the oppositely charged silica surface which means that the shorter gelling times obtained in magnesium salts mixtures are not due to inner sphere complexation of magnesium with the silica surface. Instead magnesium interacts with the silica surface through its hydrating water molecules.
  •  
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