MatOx Oy

FIN, Finland
FIN, Finland
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Laaksonen K.,Aalto University | Suomela S.,Aalto University | Puisto S.R.,MatOx Oy | Rostedt N.K.J.,MatOx Oy | And 3 more authors.
Journal of the Optical Society of America B: Optical Physics | Year: 2013

The localized surface-plasmon resonance absorption of metal nanoparticles is currently utilized in many fields such as near-infrared (NIR) curing and biomedical applications. In this paper, we study theoretically the influence of an oxide (SiO2, ZrO2, or TiO2) shell on a metal (Ag, Au, or Cu) nanoparticle from the point of view of shifting the resonance peak to a more desirable color or NIR wavelengths while conserving the intensity of the absorption or extinction peak. The computational models used in the studies include the Mie theory and the four-flux method. We find shifts of up to hundreds or even close to 1000 nm. Among the material combinations studied, the largest shifts are obtained with Ag-TiO2 core-shell nanoparticles when going from a few nanometers sized core without an oxide shell to a 100 nm size core with a 100 nm thick shell. However, the huge shifts happen together with severe intensity loss of the absorption peak, leading to a more conservative estimate of practically useful shifts of a few hundreds of nanometers. © 2013 Optical Society of America.

Kutvonen A.,Aalto University | Rossi G.,Aalto University | Rossi G.,French Institute of Health and Medical Research | Puisto S.R.,MatOx Oy | And 3 more authors.
Journal of Chemical Physics | Year: 2012

We study the influence of spherical, triangular, and rod-like nanoparticles on the mechanical properties of a polymer nanocomposite (PNC), via coarse-grained molecular dynamics simulations. We focus on how the nanoparticle size, loading, mass, and shape influence the PNC's elastic modulus, stress at failure and resistance against cavity formation and growth, under external stress. We find that in the regime of strong polymer-nanoparticle interactions, the formation of a polymer network via temporary polymer-nanoparticle crosslinks has a predominant role on the PNC reinforcement. Spherical nanoparticles, whose size is comparable to that of the polymer monomers, are more effective at toughening the PNC than larger spherical particles. When comparing particles of spherical, triangular, and rod-like geometries, the rod-like nanoparticles emerge as the best PNC toughening agents. © 2012 American Institute of Physics.

Laaksonen K.,Aalto University | Suomela S.,Aalto University | Puisto S.R.,MatOx Oy | Rostedt N.K.J.,MatOx Oy | And 3 more authors.
Journal of the Optical Society of America B: Optical Physics | Year: 2014

We perform computationally a systematic study of the optical properties of nanoscale shell-core metal-oxide particles, where a dielectric core (vacuum, SiO2, ZrO2, or TiO2) is surrounded by a metal shell (Ag, Au, or Cu). We give a detailed discussion of the observed features in the optical spectra. The calculations are done using Mie theory and the four-flux method. The optical spectra are dominated by the localized surface plasmon resonance (SPR) excitations induced by the metal shell. We find that the symmetric dipole SPR modes can be redshifted up to 1500 nm by decreasing the shell thickness down to 1 nm with a high-refractive-index core. However, this shift comes with a severe loss in the sharpness of the SPR peak as both the decrease of the shell thickness and the high-refractive-index core dampen and broaden the peak. Thus, only shifts up to 500-1000 nm are practical if good selectivity and high extinction are required, as is the case for many near-infrared absorption applications. The choice of core material was found to cause shifts of a few hundred nanometers. © 2014 Optical Society of America.

Laaksonen K.,Aalto University | Li S.-Y.,Uppsala University | Puisto S.R.,MatOx Oy | Rostedt N.K.J.,MatOx Oy | And 5 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

Spectral transmittance and reflectance in the 300-2500 nm solar-optical wavelength range were calculated for nanoparticles of titanium dioxide and vanadium dioxide with radii between 5 and 100 nm embedded in transparent dielectric media. Both of the materials are of large importance in green nanotechnologies: thus TiO2 is a photocatalyst that can be applied as a porous film or a nanoparticle composite on indoor or outdoor surfaces for environmental remediation, and VO2 is a thermochromic material with applications to energy-efficient fenestration. The optical properties, including scattering, of the nanoparticle composites were computed from the Maxwell-Garnett effective-medium theory as well as from a four-flux radiative transfer model. Predictions from these theories approach one another in the limit of small particles and in the absence of optical interference. Effects of light scattering can be modeled only by the four-flux theory, though. We found that nanoparticle radii should be less than ∼20 nm in order to avoid pronounced light scattering. © 2014 Elsevier B.V.

Merilainen A.,Aalto University | Seppala A.,Aalto University | Saari K.,Aalto University | Seitsonen J.,Aalto University | And 5 more authors.
International Journal of Heat and Mass Transfer | Year: 2013

We carry out extensive experimental studies of turbulent convective heat transfer of several water-based Al2O3, SiO2, and MgO nanofluids with a nanoparticle volume fraction up to 4%. The experimental setup consists of an annular tube, where sub-atmospheric condensing steam is used to establish a constant wall temperature boundary condition, with nanofluid forced through the inner tube. To unravel the influence of particle shape and size to heat transfer we also present a detailed characterization of the nanofluids using Dynamic Light Scattering and Transmission Electron Microscopy techniques in situ. In agreement with previous studies, we find that the average convective heat transfer coefficients of nanofluids are typically enhanced by up to 40% when compared to the base fluid on the basis of constant Reynolds number in the turbulent regime, where Re = 3000-10,000. However, the increase of the dynamic viscosity of nanofluids leads to significant pressure losses as compared to the base fluids. To account for this, the convective heat transfer efficiency η is determined by comparing the enhanced heat transfer performance to the increased pumping power requirement. When this has been properly taken into account, only the SiO2 based nanofluid with smooth spherical particles (of average size 6.5 ± 1.8 nm) shows noticeable improvement in heat transfer with a particle volume fraction of 0.5-2%. Increasing the nanoparticle volume fraction beyond 2% enhances the heat transfer coefficient but at the same time lowers heat transfer efficiency η due to pressure losses, which result from the increased fluid density and viscosity. Through our nanoparticle size and shape analysis we find that in general small, spherical and smooth particles (less than 10 nm in size) are best in enhancing heat transfer and keeping the increase of pressure losses moderate. Our results show that the nanoscale properties of the particle phase must be carefully considered in heat transfer experiments. © 2013 Elsevier Ltd. All rights reserved.

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