Philippe Rabiller

Current research
Alkane/urea inclusion compounds
Superspace
Diffuse scattering
Instrumentation
Selected publications

UNIVERSITY RENNES

Coordinator

E-mail : philippe [dot] rabilleruniv-rennes1 [dot] fr

Phone : +33 223236065

Prof. Philippe Rabiller is full professor in Physics at University of Rennes 1 (UR1), and the coordinator of the MaMaSELF program. He is also dean of ‘Beaulieu Scientific Campus’, one of the UR1 campus hosting the departments of Philosophy, Math, Electronics & Computing Science, Biology, Chemistry, Physics and Mechanical Engineering, as well as technical administrative services of the University.

Current research

Alkane/urea inclusion compounds

Prof. Philippe Rabiller is mainly involved in the analysis of phase transitions occurring in aperiodic n‑alkane/urea composites. In such compounds, the two different kinds of molecules, n‑alkane (CnH2n+2) and urea (CO(NH2)2) form two inter-modulated sub lattices. Namely the ‘host’ sub lattice made of urea molecules linked by hydrogen bonds, forms a honeycomb like hexagonal structure where parallel channels host the ‘guest’ alkane molecules which pile up in the channels as quasi 1D-chains. Since the diameter of the channels is wide (~5Å) the n‑alkane molecules are loosely held in the channels. Furthermore, for most of the alkane lengths (n ranging from 7 to 45), the ratio of the host and guest periodicity along the hexagonal axis is incommensurate (i.e. cannot be given by the ratio of two integers). Mutual interactions between the two sub lattices and aperiodicity allow for large number of degrees of freedom yielding very specific signatures in the scattering patterns that can be used to follow the very rich sequences of phase transitions in these prototype compounds.

Superspace

Each sub lattice probes the potential of the other one and thus both lattices are mutually modulated, the wavelength of the modulation function being the periodicity of the other sub lattice. The periodicity of the composite structure can be retrieved in so-called ‘superspaces’ of dimension greater than 3.

Diffuse scattering

Since alkane molecules are weekly bounded, a significant amount of disorder is present in the structure that appears as diffuse scattering in the diffraction patterns. The location and shape of the diffuse scattering can be used to probe the evolution of partial ordering of alkane molecules as function of the length of alkane molecules or external parameters as temperature or pressure.

Instrumentation

Analyzing scattering patterns of alkane/urea inclusion compounds requires high resolution experiments. Spatial high resolution is required to discriminate all main Bragg spots and intermodulation satellites. High flux and detectors with high dynamical range are also required to measure simultaneously high intensity main Bragg spots and low or very low intensity satellites or diffuse scattering. High energy resolution is finally required for inelastic scattering experiment.
Synchrotron sources and neutron reactors are naturally well adapted experimental setups. Use of such Large Scale Facilities is regularly made, at ESRF (Genoble, FR), SOLEIL (Saclay, FR), APS (Chicago, US), ILL (Grenoble, FR) and LLB (Saclay, FR).
On the other hand, a laboratory high flux high resolution setup is available at the Institute of Physics of Rennes, combining a Cu-radiation rotating anode generator together with high resolution optics and large diameter image plate detector. Experiments can be done on this platform down to 80K with nitrogen cryo-jet or down to 15K with helium cryo-jet.

Selected publications