Université de Fribourg

Improved diffusing wave spectroscopy based on the automatized determination of the optical transport and absorption mean free path

Zhang, Chi ; Reufer, Mathias ; Gaudino, Danila ; Scheffold, Frank

In: Korea-Australia Rheology Journal, 2017, vol. 29, no. 4, p. 241–247

Diffusing wave spectroscopy (DWS) can be employed as an optical rheology tool with numerous applications for studying the structure, dynamics and linear viscoelastic properties of complex fluids, foams, glasses and gels. To carry out DWS measurements, one first needs to quantify the static optical properties of the sample under investigation, i.e. the transport mean free path l* and the...

Université de Fribourg

Single step hybrid coating process to enhance the electrosteric stabilization of inorganic particles

Rufier, Chantal ; Reufer, Mathias ; Dietsch, Hervé ; Schurtenberger, Peter

In: Langmuir, 2011, vol. 27, no. 11, p. 6622–6627

We report on a single-step coating process and the resulting colloidal stability of silica-coated spindle-type hematite nanoparticles (NPs) decorated with a layer of poly(acrylic acid) (PAA) polyelectrolyte chains that are partially incorporated into the silica shell. The stability of PAA coated NPs as a function of pH and salt concentration in water was compared to bare hematite particles and...

Université de Fribourg

Magnetic properties of silica coated spindle-type hematite particles

Reufer, Mathias ; Dietsch, Hervé ; Gasser, U. ; Grobety, Bernard ; Hirt, A. M. ; Malik, Vivek Kumar ; Schurtenberger, Peter

In: Journal of Physics: Condensed Matter, 2011, vol. 23, no. 6, p. 065102

Magnetic properties of particles are generally determined from randomly oriented ensembles and the influence of the particle orientation on the magnetic response is neglected. Here, we report on the magnetic characterization of anisotropic spindle-type hematite particles. The easy axis of magnetization is within the basal plane of hematite, which is oriented perpendicular to the spindle axis. Two...

Université de Fribourg

Morphology and orientational behavior of silica-coated spindle-type hematite particles in a magnetic field probed by small-angle x-ray scattering

Reufer, Mathias ; Dietsch, Hervé ; Gasser, Urs ; Hirt, Ann ; Menzel, Andreas ; Schurtenberger, Peter

In: Journal of Physical Chemistry B, 2010, vol. 114, no. 14, p. 4763-4769

Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles are determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a core−shell model for the form factor. The particles are found to align with their long axis perpendicular to the applied field. The...

Université de Fribourg

Inorganic–organic elastomer nanocomposites from integrated ellipsoidal silica-coated hematite nanoparticles as crosslinking agents

Sánchez-Ferrer, Antoni ; Reufer, Mathias ; Mezzenga, Raffaele ; Schurtenberger, Peter ; Dietsch, Hervé

In: Nanotechnology, 2010, vol. 21, no. 18, p. 185603

We report on the synthesis of nanocomposites with integrated ellipsoidal silica-coated hematite (SCH) spindle type nanoparticles which can act as crosslinking agents within an elastomeric matrix. Influence of the surface chemistry of the hematite, leading either to dispersed particles or crosslinked particles to the elastomer matrix, was studied via swelling, scattering and microscopy...

Université de Fribourg

Brushlike interactions between thermoresponsive microgel particles

Scheffold, Frank ; Díaz-Leyva, Pedro ; Reufer, Mathias ; Braham, Nasser Ben ; Lynch, Iseult ; Harden, James L.

In: Physical Review Letters, 2010, vol. 104, no. 12, p. 128304

Using a simplified microstructural picture we show that interactions between thermosensitive microgel particles can be described by a polymer brushlike corona decorating the dense core. The softness of the potential is set by the relative thickness L0 of the compliant corona with respect to the overall size of the swollen particle R. The elastic modulus in quenched solid phases derived from the...

Université de Fribourg

Temperature-sensitive poly(N-Isopropyl-Acrylamide) microgel particles: A light scattering study

Reufer, Mathias ; Díaz-Leyva, P. ; Lynch, I. ; Scheffold, Frank

In: European Physical Journal E, 2009///doi:10.1140/epje/i2008-10387-2

We present a light scattering study of aqueous suspensions of microgel particles consisting of poly(N-Isopropyl-Acrylamide) cross-linked gels. The solvent quality for the particles depends on temperature and thus allows tuning of the particle size. The particle synthesis parameters are chosen such that the resulting high surface charge of the particles prevents aggregation even in the maximally...

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...