No abstract

No abstract

X-ray photon correlation spectroscopy and small-angle scattering measurements are presented of the dynamics and structure of concentrated suspensions of charge-stabilized polystyrene latex spheres dispersed in glycerol, for volume fractions from 3% to 52%. The static structures of the suspensions show essentially hard-sphere behavior, and the short-time dynamics shows good agreement with predictions for the wave-vector-dependent collective diffusion coefficient. However, the intermediate scattering function is found to violate a scaling behavior found previously for a sterically stabilized hard-sphere suspension.

An undulator beamline and small-angle-scattering spectrometer have been implemented at the Advanced Photon Source. The beamline is optimized for performing small-angle wide-bandpass coherent X-ray scattering measurements, and has been characterized by measuring static X-ray speckle patterns from isotropically disordered samples. Statistical analyses of the speckle patterns have been performed from which the speckle widths and contrast are extracted versus wavevector transfer and sample thickness. The measured speckle widths and contrast are compared with an approximation to the intensity correlation function and found to be in good agreement with its predictions.

We have studied Langmuir monolayers composed of mixtures of heneicosanoic acid and heneicosanol using π-A isotherms and x-ray diffraction. We find that the two materials are miscible in monolayer form. We have determined how the phase diagram of the acid evolves to that of the alcohol as the composition varies. X-ray diffraction data along isotherms and isobars show that the head–head interactions, like the tail–tail interactions, are anisotropic. The ‘‘swiveling transition’’ between phases with different tilt directions is accompanied by a rotation of the molecules about their long axes.