Intramolecular structure and energetics in supercooled water down to 255 K

We studied the structure and energetics of supercooled water by means of X-ray Raman and Compton scattering. Under supercooled conditions down to 255 K, the oxygen K-edge measured by X-ray Raman scattering suggests an increase of tetrahedral order similar to the conventional temperature effect observed in non-supercooled water. Compton profile differences indicate contributions beyond the theoretically predicted temperature effect and provide a deeper insight into local structural changes. These contributions suggest a decrease of the electron mean kinetic energy by 3.3 +/- 0.7 kJ (mol K)(-1) that cannot be modeled within established water models. Our surprising results emphasize the need for water models that capture in detail the intramolecular structural changes and quantum effects to explain this complex liquid.Peer reviewe

Structure and Dynamics of Glassy-forming Fluids.

Revealing the local order of colloidal liquids and glasses will be a breakthrough in soft matter science. Here we show first results on the structure and dynamics of a soft colloidal systems. For these systems the particle interaction can be tuned by screening the surface charge of the particles. This allows to map the phase diagram from the liquid to the glass phase even to the crystal phase.In the next step we will study the local orientational order by X-ray Cross Correlation Analysis (XCCA) as a function of the particle interactions

Alignment of spindle-shaped particles in a liquid jet studied by SAXS experiments

Colloidal dispersions under shear show non-Newtonian behavior, based ontheir microstructure, which influences macroscopic parameters, e.g. viscosityand density. Research has focused mainly on dispersions of sphericalparticles studied by rheological methods. However, particle shapeanisotropy introduces additional effects:a) The local fluid flow around a non-spherical particle is different from thataround a spherical particle.b) Non-spherical particles can orient themselves affecting the properties ofthe dispersion.c) The particles’ shape may additionally influence the particle-particleinteractions.Spindle-shaped hematite colloids (α-Fe$_{2}$O$_{3}$) are an excellent test case tostudy alignment of particles under shear using x-rays, as thecharacterization of such particles with x-ray scattering is well understood.Microfluidic liquid jets allow the unique possibility to investigate spatiallyconfined nanoscale objects under shear. This experiment provides newinsights in nano-rheology studies of spindle-shaped particles due to highshear rates ẏ > 10$^{5}$ s$^{-1}$ as compared to conventional rheometers