ABSTRACT
We report on an x-ray photon correlation spectroscopy experiment investigating the surface structure and dynamics of colloidal particles suspended in a supercooled viscous liquid. The static structure factor in the direction parallel and perpendicular to the surface reveals a more disordered structure at the surface as compared to the bulk. The particles display heterogeneous ballistic dynamics parallel to the surface. The particle dynamics in the direction perpendicular to the surface is much slower and does not show the hallmarks of ballistic motion.
ABSTRACT
We introduce a new dynamic light scattering method, termed photon correlation imaging, which enables us to resolve the dynamics of soft matter in space and time. We demonstrate photon correlation imaging by investigating the slow dynamics of a quasi-two-dimensional coarsening foam made of highly packed, deformable bubbles and a rigid gel network formed by dilute, attractive colloidal particles. We find the dynamics of both systems to be determined by intermittent rearrangement events. For the foam, the rearrangements extend over a few bubbles, but a small dynamical correlation is observed up to macroscopic length scales. For the gel, dynamical correlations extend up to the system size. These results indicate that dynamical correlations can be extremely long-ranged in jammed systems and point to the key role of mechanical properties in determining their nature.
ABSTRACT
We present a new method to extract the intermediate scattering function from series of coherent diffraction patterns taken with 2D detectors. Our approach is based on analyzing speckle patterns in terms of photon statistics. We show that the information obtained is equivalent to the conventional technique of calculating the intensity autocorrelation function. Our approach represents a route for correlation spectroscopy on ultrafast timescales at X-ray free-electron laser sources.
Subject(s)
X-Rays , Kinetics , Lasers , Normal Distribution , Optics and Photonics , Pattern Recognition, Automated , Scattering, Radiation , Surface Properties , Synchrotrons , X-Ray Diffraction/methodsABSTRACT
Repulsive magnetic fluids show a dynamical freezing above a volume fraction Φ(*), which depends on the physico-chemistry of the system. Φ(*) is here determined by a magneto-optical technique. The out-of-equilibrium dynamics of a glass-forming magnetic fluid (Φ = 1.2Φ(*)) is studied by x-ray photon correlation spectroscopy and analyzed in terms of intensity auto-correlation functions. The relaxation is age dependent and follows a compressed exponential law with a characteristic time scaling as the inverse of the scattering vector Q. The dynamical susceptibility χ is then deduced from a time resolved correlation analysis at an intermediate Q and for ages larger than 10(4) s.
ABSTRACT
The control of oils and fats requires analytical processes far surpassing the traditional framework of physical properties and chemical characteristics. The control of cod liver oil is improved by the use of these procedures. The present report is devoted to the measurement of vitamin A by ultraviolet spectrophotometry and of vitamin D3 by high performance liquid chromatography, to the determination of the profile of their fatty acids and polyunsaturated fats, as well as to their measurement by liquid gas chromatography after derivatisation. The results permit the definition of the cod liver oil's quality, the differentiation between fish oils and the detection of possible changes. A technique for verifying the absence of butylhydroxyanisol and of butylhydroxytoluen is also described.
