Université de Fribourg

Impact of volume transition on the net charge of poly-$N$-isopropyl acrylamide microgels

Braibanti, Marco ; Haro-Pérez, Catalina ; Quesada-Pérez, M. ; Rojas-Ochoa, Luis Fernando ; Trappe, Véronique

In: Physical Review E, 2016, vol. 94, no. 3, p. 032601

We explore the electrostatic properties of poly-N-isopropyl acrylamide microgels in dilute, quasi-de-ionized dispersions and show that the apparent net charge of these thermosensitive microgels is an increasing function of their size, the size being conveniently varied by temperature. Our experimental results obtained in a combination of light scattering, conductivity, and mobility...

Université de Fribourg

Dynamic arrest in charged colloidal systems exhibiting large-scale structural heterogeneities

Haro-Pérez, C. ; Rojas-Ochoa, Luis Fernando ; Castañeda-Priego, R. ; Quesada-Pérez, M. ; Callejas-Fernández, J. ; Hidalgo-Álvarez, R. ; Trappe, Véronique

In: Physical Review Letters, 2009, vol. 102, no. 1, p. 018301

Suspensions of charged liposomes are found to exhibit typical features of strongly repulsive fluid systems at short length scales, while exhibiting structural heterogeneities at larger length scales that are characteristic of attractive systems. We model the static structure factor of these systems using effective pair interaction potentials composed of a long-range attraction and a shorter range...

Université de Fribourg

Density dependent interactions and structure of charged colloidal dispersions in the weak screening regime

Rojas-Ochoa, Luis Fernando ; Castañeda-Priego, R. ; Lobaskin, V. ; Stradner, Anna ; Scheffold, Frank ; Schurtenberger, Peter

In: Physical Review Letters, 2008, vol. 100, p. 178304

We determine the structure of charge-stabilized colloidal suspensions at low ionic strength over an extended range of particle volume fractions using a combination of light and small angle neutron scattering experiments. The variation of the structure factor with concentration is analyzed within a one-component model of a colloidal suspension. We show that the observed structural behavior...

Université de Fribourg

Transport of light in amorphous photonic materials

Reufer, Mathias ; Rojas-Ochoa, Luis Fernando ; Eiden, Stefanie ; Sáenz, Juan José ; Scheffold, Frank

In: Applied Physics Letters, 2007, vol. 91, no. 17, p. 171904

Amorphous photonic materials based on dense assemblies of high refractive index spherical particles are presented. Light transmission through these photonic glasses shows a nontrivial wavelength dependence. The transmission spectra can be quantitatively reproduced by modeling the optical properties starting from their building blocks. Our results emphasize the relevance of including short range...

Université de Fribourg

The influence of the scattering anisotropy parameter on diffuse reflection of light

Pierrat, R. ; Ben Braham, Nasser ; Rojas-Ochoa, Luis Fernando ; Carminati, R. ; Scheffold, Frank

In: Optics Communications, 2008, vol. 281, no. 1, p. 18-22

We discuss the impact of the scattering anisotropy parameter on the path length distribution of multiply scattered light. A quantitative treatment based on the radiative transfer equation is compared to an extended photon diffusion formalism. We compare both models with diffusing-wave spectroscopy measurements using randomly polarized light.

Université de Fribourg

Photonic properties of strongly correlated colloidal liquids

Rojas-Ochoa, Luis Fernando ; Mendez-Alcaraz, J. M. ; Sáenz, J. J. ; Schurtenberger, Peter ; Scheffold, Frank

In: Physical Review Letters, 2004, vol. 93, p. 073903-73906

The optical and structural properties of dense colloidal suspensions in the presence of long-range electrostatic repulsion are determined from both light and small-angle neutron scattering experiments. Short-range structural order induces an enhancement of the scattering strength while at the same time the total transmission shows strong wavelength dependence, reminiscent of a photonic crystal....

Université de Fribourg

Depolarization of backscattered linear lypolarized ligh

Rojas-Ochoa, Luis Fernando ; Lacoste, David ; Lenke, Ralf ; Schurtenberger, Peter ; Scheffold, Frank

In: Journal of the Optical Society of America: A, 2004, vol. 21, p. 1799-1804

We formulate a quantitative description of backscattered linearly polarized light with an extended photon diffusion formalism taking explicitly into account the scattering anisotropy parameter g of the medium. From diffusing wave spectroscopy measurements, the characteristic depolarization length for linearly polarized light, lp, is deduced. We investigate the dependence of this length on the...