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Université de Fribourg

A general method to label metal oxide particles with fluorescent dyes using aryldiazonium salts

Dechézelles, Jean-François ; Griffete, Nébéwia ; Dietsch, Hervé ; Scheffold, Frank

In: Particle & Particle Systems Characterization, 2013, p. -

Different metal oxide particles are dye labeled by a novel and versatile approach based on aryldiazonium salt chemistry. For dye labeling the particles, the simplicity of aryldiazonium salts to be grafted onto metallic or metal oxide surface is advantageous. The salt is used as a linking agent for attaching the fluorescent molecules.

Université de Fribourg

Mass transport properties of the tetrahydronaphthalene/n-dodecane mixture measured by investigating non-equilibrium fluctuations

Croccolo, Fabrizio ; Scheffold, Frank ; Bataller, Henri

In: Comptes Rendus Mécanique, 2013, vol. 341, no. 4–5, p. 378–385

We present preliminary near-field light scattering (NFS) data concerning the analysis of the static power spectrum and of the relaxation time constant as a function of the wave vector for non-equilibrium fluctuations (NEFs). The goal of these measurements is to obtain information about the Soret and the mass diffusion coefficients of a binary mixture undergoing thermodiffusion. In particular, we...

Université de Fribourg

A light scattering study of non equilibrium fluctuations in liquid mixtures to measure the Soret and mass diffusion coefficient

Croccolo, Fabrizio ; Bataller, Henri ; Scheffold, Frank

In: Journal of Chemical Physics, 2012, vol. 137, no. 23, p. 234202

We use dynamic near field scattering to measure the dynamics of concentration non equilibrium fluctuations at the steady-state of Soret separation. The analysis reveals that above a threshold wave vector qc, the dynamics is governed by diffusion while at smaller wave vectors, gravity dominates. From the measurements, we extract both the mass diffusion and the Soret...

Université de Fribourg

Quasi-real-time analysis of dynamic near field scattering data using a graphics processing unit

Cerchiari, Giovanni ; Croccolo, Fabrizio ; Cardinaux, Frédéric ; Scheffold, Frank

In: Review of Scientific Instruments, 2012, vol. 83, no. 10, p. 106101

We present an implementation of the analysis of dynamic near field scattering (NFS) data using a graphics processing unit. We introduce an optimized data management scheme thereby limiting the number of operations required. Overall, we reduce the processing time from hours to minutes, for typical experimental conditions. Previously the limiting step in such experiments, the processing time is now...

Université de Fribourg

Rapid high resolution imaging of diffusive properties in turbid media

Scheffold, Frank ; Block, Ian D.

In: Optics Express, 2012, vol. 20, no. 1, p. 192-200

We propose a laser speckle based scheme that allows the analysis of local scattering properties of light diffusely reflected from turbid media. This turbid medium can be a soft material such as a colloidal or polymeric material but can also be biological tissue. The method provides a 2D map of the scattering properties of a complex, multiple scattering medium by recording a single image. We...

Université de Fribourg

Negative scattering asymmetry parameter for dipolar particles: Unusual reduction of the transport mean free path and radiation pressure

Gómez-Medina, R. ; Froufe-Pérez, L. S. ; Yépez, M. ; Scheffold, Frank ; Nieto-Vesperinas, M. ; Sáenz, Juan José

In: Physical Review A - Atomic, molecular and optical physics, 2012, vol. 85, no. 3, p. 035802

Lossless dielectric nanospheres (made of nonmagnetic materials) with relatively low refraction index may present strong electric and magnetic dipolar resonances. We establish a relationship between the optical force from a plane wave on small electric and magnetic dipolar particles, the transport cross section, and the scattering asymmetry parameter g. In this way we predict negative g (that...

Université de Fribourg

Magnetic orientation of soft particles in a jammed solid

Dagallier, Camille ; Cardinaux, Frédéric ; Dietsch, Hervé ; Scheffold, Frank

In: Soft Matter, 2012, vol. 8, no. 15, p. 4067-4071

Densely packed atoms, molecules, or small particles can get trapped in a jammed state thereby avoiding crystallization. The resulting amorphous structures display complex, spatially heterogeneous, trapping potentials in stark contrast to the uniform case of a crystal. Here we study active and passive rotational motion in a jammed colloidal dispersion of particles consisting of an...

Université de Fribourg

Photon path length distribution in random media from spectral speckle intensity correlations

Rojas, L.F. ; Bina, M. ; Cerchiari, G. ; Escobedo-S´anchez, M.A. ; Ferri, F. ; Scheffold, Frank

In: The European Physical Journal - Special Topics, 2011, vol. 199, no. 1, p. 167-180

We show that the spectral speckle intensity correlation (SSIC) technique can be profitably exploited to recover the path length distribution of photons scattered in a random turbid medium. We applied SSIC to the study of Teflon slabs of different thicknesses and were able to recover, via the use of the photon diffusion approximation theory, the characteristic transport mean free path ℓ∗ and...

Université de Fribourg

Follow-up of cortical activity and structure after lesion with laser speckle imaging and magnetic resonance imaging in nonhuman primates

Peuser, Jörn ; Belhaj-Saif, Abderraouf ; Hamadjida, Adjia ; Schmidlin, Eric ; Gindrat, Anne-Dominique ; Völker, Andreas Charles ; Zakharov, Pavel ; Hoogewoud, Henri-Marcel ; Rouiller, Eric M. ; Scheffold, Frank

In: Journal of Biomedical Optics, 2011, vol. 16, no. 09, p. 096011

The nonhuman primate model is suitable to study mechanisms of functional recovery following lesion of the cerebral cortex (motor cortex), on which therapeutic strategies can be tested. To interpret behavioral data (time course and extent of functional recovery), it is crucial to monitor the properties of the experimental cortical lesion, induced by infusion of the excitotoxin ibotenic acid. In...

Université de Fribourg

Strong magnetic response of submicron Silicon particles in the infrared

García-Etxarri, A. ; Gómez-Medina, R. ; Froufe-Pérez, L. S. ; López, C. ; Chantada, L. ; Scheffold, Frank ; Aizpurua, J. ; Nieto-Vesperinas, M. ; Sáenz, Juan José

In: Optic Express, 2011, vol. 19, no. 6, p. 4815

High-permittivity dielectric particles with resonant magnetic properties are being explored as constitutive elements of new metamaterials and devices. Magnetic properties of low-loss dielectric nanoparticles in the visible or infrared are not expected due to intrinsic low refractive index of optical media in these regimes. Here we analyze the dipolar electric and magnetic response of lossless...