Introduction

Soft condensed matter science accounts for about 15% of User activities at the ESRF. It is a broad discipline that addresses questions concerning the microstructure, kinetics, dynamics and rheology of complex and nano-structured materials (polymers, colloids, fluids, liquid crystals, etc.) in 3D and under reduced dimensionality. Many experiments are concerned with the structure determination of thin organic films and membranes or diffraction from fibres, small unit cell systems and biological entities. They also involve studies of in situ processing, site-selective chemistry and tailoring of molecular assemblies. This research is carried out at several beamlines and has been supported since January 2002 by a newly formed Soft Condensed Matter Group, comprising the insertion device beamlines ID02, ID10A, ID10B and ID13. Similar activities are pursued at the CRG beamlines BM02, BM26 and BM32. The borders with neighbouring disciplines such as life sciences, surface- and interface physics, chemistry and materials science have become increasingly transparent. This is aided by constant progress at beamlines (availability of micrometre and submicrometre-sized and/or coherent X-ray beams, two-dimensional detectors with high spatial and temporal resolution, advanced sample environments) and the large variety of available measuring techniques. Key techniques are single crystal diffraction as well as small-angle and wide-angle scattering (µSAXS/WAXS) with microbeams at ID13, time-resolved small-angle and wide-angle scattering (SAXS/WAXS) and ultra small-angle scattering (USAXS) at ID02, high-resolution diffraction and reflectometry (XRD, XRR) and X-ray photon correlation spectroscopy (XPCS) at ID10A, and grazing-incidence diffraction (GID), X-ray reflectometry (XRR) and grazing-incidence small-angle scattering (GISAXS) at ID10B.

In 2002, the main technical developments at ID02 were commissioning of the bypass SAXS camera for experiments requiring special detectors, as well as improvements in photon flux and sensitivity of the SAXS detector (resulting in a combined gain of five). Moreover, a new rheometer was added to the list of sample environments, allowing low stress level and transient rheological measurements together with combined small- and wide-angle (SAXS and WAXS) scattering. Selected scientific highlights include studies of millisecond range structural transformations in micellar solutions [1], microdomain ordering in block copolymers [2]and work tracing the mineral lyotropic liquid-crystalline phase of magnetic nanorods [3]. The interference effect in the muscle myosin diffraction was further exploited to shed new light on the mechanism of muscle contraction [4]. Other noteworthy examples include the elucidation of the counter-ion distribution in spherical polyelectrolyte brushes by anomalous SAXS (collaboration between the Polymer Institut at U. Karlsruhe/Germany and ID02), and probing the evolution of microstructure and dynamics (collaboration with ID10A) in attractive colloidal systems.

The ID10A beamline keeps its multipurpose character, accepting experiments from the soft condensed matter, surface and interface, methods and instrumentation and hard condensed matter communities. An example of activities in the latter discipline is a study of the motional ordering of a charge-density wave in the sliding state [5]. Another speciality of ID10A lies in the field of slow dynamics studied by means of photon correlation spectroscopy (XPCS) with coherent X-ray beams. In the domain of soft condensed matter, two-dimensional detection has been used to investigate very slow dynamics and ageing phenomena in non-ergodic glassy materials. Fast, zero-dimensional detection has been used to study layer-displacement fluctuations in smectic membranes [6]. We can identify two main poles of interest for in-house research. The first concerns investigating the structure and dynamics of colloidal suspensions, from glassy systems (highly-concentrated colloidal suspensions, colloid-polymer mixtures and polymer gels) to charged or magnetically-interacting systems. The second concerns the study of (surface) dynamics in "simple" or complex liquids. Recent work on the critical viscosity at the free surface of a liquid crystal is featured in the following highlights section.

The ID10B (Troika II) beamline is the only beamline at the ESRF that routinely provides all surface diffraction techniques for the study of liquid surfaces and interfaces and length-scales from sub-nm to 100 nm (in some cases even up to 1000 nm). A recent upgrade of the deflector stage allows us now to reach a momentum transfer of Qz = 8 nm-1 in a reflectivity experiment on a liquid surface. In 2003 the beamline will install a system to focus the X-ray beam vertically thus providing a significant gain in flux. In-house research is predominantly focused on structural studies of liquid and complex fluid (colloid, sol, gel) interfaces, two-dimensional assemblies of molecules and macromolecules formed at such interfaces and the interaction of these monomolecular films with supporting media [7]. Interaction of antimicrobial peptides with prokaryotic and euprokaryotic cell membranes mimicked by different phospholipid monolayers is presented as an example in this year's highlights [8].

On ID13 a second experimental hutch has been commissioned for µSAXS/µWAXS with a dedicated Kirkpatrick-Baez optics. A new in-vacuum undulator optimised for about 13 keV now complements the original tuneable undulator. The use of sub-µm optics, like waveguide or Fresnel optics was further explored for different materials including semiconductors, biopolymers and polymers. Thus scanning µWAXS with a waveguide beam of about 100 nm across Kevlar fibres and modelling the data with Monte Carlo methods could evidence differences in rotational disorder [9]. Micro-deformation remained a very active field and several polymeric materials have been studied, when subjected to various deformation tests (e.g. cold drawing [10] or stress oscillation during static loading). Furthermore, µSAXS craze field scanning in deformed industrial samples was performed and modelled. A micro-hardness setup has been commissioned and allowed us to perform in situ µWAXS experiments during indentation [11]. The microgoniometer has been available on a regular basis for protein crystallography experiments. Several small unit cell experiments were performed using the detector rotating-arm. The flexibility of this setup has also been demonstrated in µSAXS experiments on single cell nuclei.

The following selected highlights reflect both the wide variety of subjects and the specific strengths of individual beamlines. The first contribution shows how the beam from a bending magnet beamline (BM26) can be used to illustrate the self-organisation of colloidal hard sphere particles into a crystalline structure. In the second contribution the superior brilliance of an insertion device beamline (ID10A) is used to produce a coherent X-ray beam thus enabling the study of the critical behaviour of the viscosity of a liquid crystal at the nematic-smecticA phase transition in 8OCB. In a beautiful experiment at ID02 high-resolution SAXS and WAXS were used to illustrate the hierarchical self-organisation of nanotubes. The interaction of antimicrobial peptides with prokaryotic and euprokaryotic cell membranes mimicked by different phospholipid monolayers was studied by reflectivity and grazing-incidence techniques at ID10B. Finally, micro-SAXS at ID13 was used to unravel the (twisted plywood) diffraction pattern of collagen fibrils in fish scales.

 

References
[1] S. Schmölzer et al., Phys. Rev. Lett. 88, 258301-1 (2002).
[2] A. Böker et al., Phys. Rev. Lett. 89, 135502-1 (2002).
[3] B.J. Lemaire et al., Phys. Rev. Lett. 88, 125507-1 (2002).
[4] G. Piazzesi et al., Nature 415, 659 (2002).
[5] R. Danneau et al., Phys. Rev. Lett. 89, 106404-1 (2002).
[6] I. Sikharulidze et al., Phys. Rev. Lett., 88, 115503-1 (2002).
[7] B. Struth et al., Phys. Rev. Lett. 88, 025502-1 (2002).
[8] O. Konovalov et al., European Biophysics Journal, 31, 428 (2002).
[9] S. Roth et al., Macromolecules, in press.
[10] M.C. Garcia-Gutiérrez et al., Macromolecules 35, 7320 (2002).
[11] A. Gourrier et al., Macromolecules 35, 8072 (2002).