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We report the observation of a new type of columnar liquid crystal phase, which is formed by thin hard colloidal disks in a dense suspension. High-resolution small-angle x-ray diffraction reveals a combination of long-range bond-orientational order and short-range translational order between the columns, the hallmark of the hexatic phase. Our results imply that geometric frustration related to the size polydispersity of the particles destroys long-range translational order and therefore promotes the formation of this novel phase.

High-resolution synchrotron small-angle x-ray diffraction is applied to characterize the structure and long-range order in a sedimentary hard-sphere colloidal crystal before and during its drying. The principles of the technique and the influence of the coherence properties of the x-ray beam are discussed in detail. The capillary forces generated during the drying process are shown to destroy the long-range order and to break the crystal into smaller crystallites with slightly different orientations. The diffraction is shown to switch from the dynamic regime in the long-range-ordered crystal to nearly kinematic diffraction in the mosaic (short-range-ordered) crystal.

We report combined x-ray photon correlation spectroscopy (XPCS) and neutron spin echo (NSE) measurements of the layer-displacement fluctuations in smectic liquid-crystal membranes in the range from 10 ns to 10 micros. NSE reveals a new regime, determined by bulk elasticity, in which relaxation times decrease with the wave vector of the fluctuations. XPCS probes slower surface-tension-dominated relaxation times, independent of the wave vector. XPCS gives a difference in correlation times at specular and off-specular positions that can be related to different detection schemes.

Synchrotron small-angle x-ray diffraction images of random-stacking-induced Bragg scattering rods are obtained in a wide range of wave vectors from a single colloidal crystal. The results reveal a strong multiple scattering effect, which leads to new features in the diffraction pattern-secondary Bragg rods. We argue that dynamic x-ray diffraction is rather common for high-quality colloidal photonic crystals and should be taken into account.

The long-range order parameters in single crystals of hard colloidal spheres grown in sediments of colloid-polymer mixtures are determined using synchrotron small-angle x-ray diffraction with a resolution of 10(-6) of the wave vector. The interplanar positional order derived from the width of lattice reflections extends over at least 500 lattice planes. The lattice planes are orientationally correlated within approximately 0.1 degrees throughout the crystals, whereas the stacking of hexagonal planes remains random.

The dynamics of the layer-displacement fluctuations in smectic membranes have been studied by x-ray photon correlation spectroscopy (XPCS). We report transitions from an oscillatory damping regime to simple exponential decay of the fluctuations, both as a function of membrane thickness and upon changing from specular to off-specular scattering. This behavior is in agreement with recent theories. Employing avalanche photodiode detectors and the uniform filling mode of the synchrotron storage ring, the fast limits of XPCS have been explored down to 50 ns.

Static and dynamic x-ray scattering has been used to characterize thermal fluctuations in free-standing smectic films in the crystalline-B phase. The results are remarkably similar to those in smectic-A films, in spite of the three-dimensional positional order in the crystalline-B phase. The main difference is the disappearance of the characteristic Landau-Peierls instability of the smectic-A phase. The dynamic nature of the fluctuations is explicitly demonstrated by x-ray photon correlation spectroscopy. This fluctuation behavior of crystalline-B films can be attributed to the small value of the shear elastic constant C44.

Coherent dynamic x-ray scattering has been used to study the thermally excited layer fluctuations in freely suspended smectic films of the compound 4O.8. Using 8-keV x rays and films with a thickness around 0.3 &mgr;m we resolve relaxation times down to a few &mgr;s. A combination of damped and oscillatory behavior is observed for the layer undulations, which can be attributed to inertial effects. These are due to the surface contribution to the free energy which cannot be disregarded for thin films.