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Particle interactions at the nanoscale: From colloidal processing to self-assembled arrays
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2012 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University , 2012. , 96 p.
Keyword [en]
Colloidal processing, nanoparticles, colloidal forces, titania, iron oxide, Hamaker constant, surface modification, rheology, Monte Carlo simulations, collective properties, superparamagnetism, finite-size effects
National Category
Nano Technology
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-79129ISBN: 978-91-7447-570-8 (print)OAI: oai:DiVA.org:su-79129DiVA: diva2:547609
Public defence
2012-09-28, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

Available from: 2012-09-06 Created: 2012-08-28 Last updated: 2013-09-17Bibliographically approved
List of papers
1. Hamaker Constants of Iron Oxide Nanoparticles
Open this publication in new window or tab >>Hamaker Constants of Iron Oxide Nanoparticles
2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 14, 8659-8664 p.Article in journal (Refereed) Published
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.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-66568 (URN)10.1021/la201387d (DOI)000292617800009 ()
Note
authorCount :3Available from: 2011-12-21 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
2. 2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals
Open this publication in new window or tab >>2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals
Show others...
2013 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 5, no 3, 953-960 p.Article in journal (Refereed) Published
Abstract [en]

The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain gamma-Fe2O3 spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using the structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with the experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions.

National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-88309 (URN)10.1039/c2nr33013j (DOI)000313803000019 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

AuthorCount:13;

Available from: 2013-03-19 Created: 2013-03-12 Last updated: 2017-12-06Bibliographically approved
3. Rapid detection of trace amounts of surfactants using nanoparticles in fluorometric assays
Open this publication in new window or tab >>Rapid detection of trace amounts of surfactants using nanoparticles in fluorometric assays
Show others...
2010 (English)In: Nanoscale, ISSN 2040-3364, Vol. 2, no 1, 69-71 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Cambridge (Thomas Graham House), UK: The Royal Society of Chemistry, 2010
Keyword
nanoparticles, fluorometric assays
National Category
Inorganic Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-46198 (URN)10.1039/b9nr00172g (DOI)000275164400005 ()
Funder
Swedish Research Council
Note

authorCount :7

Available from: 2010-11-26 Created: 2010-11-23 Last updated: 2012-08-28Bibliographically approved
4. Spray drying of TiO2 nanoparticles into redispersible granules
Open this publication in new window or tab >>Spray drying of TiO2 nanoparticles into redispersible granules
Show others...
2010 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, no 2, 384-388 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier B.V., 2010
Keyword
Nanoparticle, Spray drying, Granule, Dispersion, Titania
National Category
Inorganic Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-46703 (URN)10.1016/j.powtec.2010.05.033 (DOI)000281461700031 ()
Projects
European Project “SAPHIR—Safe, integrated & controlled production of high-tech multifunctional materials and their recycling”.
Funder
EU, European Research Council
Available from: 2010-11-26 Created: 2010-11-24 Last updated: 2017-12-12Bibliographically approved

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