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  • 1.
    Faure, Bertrand
    Stockholm University.
    Dispersion and incorporation of titania nanoparticles into mesoporous silica2006Licentiate thesis, monograph (Other academic)
  • 2.
    Faure, Bertrand
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Particle interactions at the nanoscale: From colloidal processing to self-assembled arrays2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanostructured materials are the next generation of high-performance materials, harnessing the novel properties of their nanosized constituents. The controlled assembly of nanosized particles and the design of the optimal nanostructure require a detailed understanding of particle interactions and robust methods to tune them. This thesis describes innovative approaches to these challenges, relating to the determination of Hamaker constants for iron oxide nanoparticles, the packaging of nanopowders into redispersible granules, the tuning of the wetting behavior of nanocrystals and the simulation of collective magnetic properties in arrays of superparamagnetic nanoparticles.

    The non-retarded Hamaker constants for iron oxides have been calculated from their optical properties based on Lifshitz theory. The results show that the magnitude of vdW interactions in non-polar solvents has previously been overestimated up to 10 times. Our calculations support the experimental observations that oleate-capped nanoparticles smaller than 15 nm in diameter can indeed form colloidally-stable dispersions in hydrocarbons. In addition, a simple procedure has been devised to remove the oleate-capping on the iron oxide nanoparticles, enabling their use in fluorometric assays for water remediation, with a sensitivity more than 100 times below the critical micelle concentration for non-ionic surfactants.

    Nanosized particles are inherently more difficult to handle in the dry state than larger micron-sized powders, e.g. because of poor flowability, agglomeration and potential toxicity. The rheology of concentrated slurries of TiO2 powder was optimized by the addition of sodium polyacrylate, and spray-dried into fully redispersible micron-sized granules. The polymer was embedded into the granules, where it could serve as a re-dispersing aid.

    Monte Carlo (MC) simulations have been applied to the collective magnetic behavior of nanoparticle arrays of various thicknesses. The decrease in magnetic susceptibility with the thickness observed experimentally was reproduced by the simulations. Ferromagnetic couplings in the arrays are enhanced by the finite thickness, and decrease in strength with increasing thickness. The simulations indicate the formation of vortex states with increasing thickness, along with a change in their orientation, which becomes more and more isotropic as the thickness increases.

  • 3.
    Faure, Bertrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hamaker Constants of Iron Oxide Nanoparticles2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 14, p. 8659-8664Article in journal (Refereed)
    Abstract [en]

    The Hamaker constants for iron oxide nanoparticles in various media have been calculated using Lifshitz theory. Expressions for the dielectric responses of three iron oxide phases (magnetite, maghemite, and hematite) were derived from recently published optical data. The nonretarded Hamaker constants for the iron oxide nanopartides interacting across water, A(1w1) = 33 - 39 zJ, correlate relatively well with previous reports, whereas the calculated values in nonpolar solvents (hexane and toluene), A(131) = 9 29 zJ, are much lower than the previous estimates, particularly for magnetite. The magnitude of van der Waals interactions varies significantly between the studied phases (magnetite < maghemite < hematite), which highlights the importance of a thorough characterization of the particles. The contribution of magnetic dispersion interactions for particle sizes in the superparamagnetic regime was found to be negligible. Previous conjectures related to colloidal stability and self-assembly have been revisited on the basis of the new Lifshitz values of the Hamaker constants.

  • 4.
    Faure, Bertrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Sæderup Lindeløv, Jesper
    Wahlberg, Michael
    Adkins, Nicholas
    Jackson, Phil
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Spray drying of TiO2 nanoparticles into redispersible granules2010In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, no 2, p. 384-388Article in journal (Refereed)
    Abstract [en]

    We have demonstrated how titania nanoparticles can be spray-dried to produce redispersible granules. Theevaluation of different dispersants using rheology, particle size and electrokinetic measurements showedthat an anionic carboxylated polyelectrolyte, Dispex N40, was able to stabilize the primary aggregates of thetitania nanoparticles with a size of about 180 nm at an addition of 2.4% dry-weight basis over a relativelylarge pH-range. Transmission electron microscopy showed that the commercial P-25 titania nanopowdercould not be deagglomerated down to the individual crystallite size of 15–40 nm. Spherical granules with asize between 20 and 50 μm and a minimum amount of dusty fines could be produced by spray drying theaqueous titania dispersions in a configuration with internal bag filters. The granules could be completelydisintegrated and redispersed in water by ultrasonication into a stable suspension with a size distributionthat is identical to the as-received powder. The possibility to prepare redispersible nanoparticle granules byspray drying is a route to minimize the risk of airborne exposure and facilitate the handling of nanopowders.

  • 5.
    Härma, Harri
    et al.
    Laboratory of Biophysics and Medicity,University of Turku, Finland.
    Laakso, Susana
    Laboratory of Biophysics and Medicity,University of Turku, Finland.
    Pihlasalo, Sari
    Laboratory of Biophysics and Medicity,University of Turku, Finland.
    Hänninen, Pekka
    Laboratory of Biophysics and Medicity,University of Turku, Finland.
    Faure, Bertrand
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Rana, Subhasis
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Rapid detection of trace amounts of surfactants using nanoparticles in fluorometric assays2010In: Nanoscale, ISSN 2040-3364, Vol. 2, no 1, p. 69-71Article in journal (Refereed)
    Abstract [en]

    Rapid microtiter assays that utilize the time-resolved fluorescenceresonance energy transfer or quenching of dye-labeled proteinsadsorbed onto the surfaces of polystyrene or maghemite nanoparticleshave been developed for the detection and quantification oftrace amounts of surfactants at concentrations down to 10 nM.

  • 6.
    Vasiliev, Petr
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Faure, Bertrand
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Ng, Boon Sing
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Colloidal aspects relating to direct incorporation of TiO2 nanoparticles into mesoporous spheres by an aerosol-assisted process2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 319, no 1, p. 144-151Article in journal (Refereed)
    Abstract [en]

    Titania nanoparticles have been incorporated into spherical mesoporous silica powders by an aerosol-assisted synthesis process from both aqueous and ethanol-based precursor dispersions. Transmission electron microscopy (TEM) showed that the titania nanoparticles exist as single particles or small aggregates within the mesoporous carrier particles and analysis of the nitrogen adsorption isotherms proved that the pore blocking of the particles is small. Particle size and zeta potential measurements showed that the addition of tetraethoxysiloxane (TEOS), and also hexadecyl trimethyl ammonium bromide (C16TAB) induced flocculation of the TiO2 nanoparticles. The higher yield and narrower size distribution of the composite powder produced from ethanol-based dispersions compared to the aqueous dispersions could be related to a smaller degree of aggregation, indicated by rheological measurements.

     

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