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

Correlation between morphology, water uptake, and proton conductivity in radiation-grafted proton-exchange membranes

Balog, Sandor ; Gasser, Urs ; Mortensen, Kell ; Gubler, Lorenz ; Scherer, Guenther G. ; youcef, Hicham Ben

In: Macromolecular Chemistry and Physics, 2010, vol. 211, no. 6, p. 635-643

An SANS investigation of hydrated proton exchange membranes is presented. Our membranes were synthesized by radiation-induced grafting of ETFE with styrene in the presence of a crosslinker, followed by sulfonation of the styrene. The contrast variation method was used to understand the relationship between morphology, water uptake, and proton conductivity. The membranes are separated into two...

Université de Fribourg

Deswelling microgel particles using hydrostatic pressure

Lietor-Santos, Juan-Jose ; Sierra-Martin, Benjamin ; Vavrin, Ronny ; Hu, Zhibing ; Gasser, Urs ; Fernandez-Nieves, Alberto

In: Macromolecules, 2009, vol. 42, no. 16, p. 6225–6230

We report on the use of hydrostatic pressure, P, to deswell thermosensitive poly(N-isopropylacrylamide) (pNIPAM) microgels and show that it can affect the polymer−solvent mixing as much as temperature, which is the traditional variable used to deswell pNIPAM particles. Interestingly, the microgel volume changes more gradually with pressure than it does with temperature. By comparing the...

Université de Fribourg

Crystallization in three- and two-dimensional colloidal suspensions

Gasser, Urs

In: Journal of Physics: Condensed Matter, 2009, vol. 21, no. 20, p. 203101

Despite progress in the understanding of crystal nucleation and crystal growth since the first theories for nucleation were developed, an exact quantitative prediction of the nucleation rates in most systems has remained an unsolved problem. Colloidal suspensions show a phase behavior that is analogous to atomic or molecular systems and serve accordingly as ideal model systems for studying...

Université de Fribourg

Crystal structure of highly concentrated, ionic microgel suspensions studied by neutron scattering

Gasser, Urs ; Sierra-Martin, B. ; Fernandez-Nieves, A.

In: Physical Review, 2009, vol. 79, no. 5, p. 051403

We present a neutron-scattering investigation of the crystal structure formed by pH-sensitive poly(2-vinylpyridine) microgel particles with 5 wt % of cross-linker. We focus on highly swollen particles and explore concentrations ranging from below close packing to well above close packing, where the particles are forced to shrink and/or interpenetrate. The crystal structure is found to be random...