Fluoro-alkane Amphiphile diblocks for Non-aqueous soft-Templating Approaches – a route to SiC with controlled porosity – FANTA-SiC

A so-called «soft-templating« approach is used in order to control the structure of SiC. In this approach, amphiphilic molecules of the fluoroalkane type are used. These molecules are able to self-aggregate in a solution of SiC molecular precursors. The washing of these fluoroalkane aggregates generates pores in the final material. The heart of this project is the understanding of the self-aggregation mechanisms of fluoroalkanes in the medium constituted by the SiC precursors.

Silicon-bearing molecules indended for being SiC precursors were synthesized: trisilacyxlohexane (TSCH). Such a molecule respects the Si:C stoichiometry. Mixtures of cyclohexane, a simulating molecule of TSCH, and a few semifluoroalkanes were made and analyzed using Small Angle X-ray Scattering (SAXS).

Structural studies based on SAXS in mixtures involving TSCH will begin. The identification of composition domains where an organisation at the mesoscopic scale is found will allow starting the polymerization of the TSCH molecules around semifluoroalkanes aggregates. Then the clearing of these aggregates will allow calcinating the material in order to obtain the SiC.

For the moment, the project did not result in any publication or patent.

This project is dedicated to fundamental research on structural organisation mechanisms in totally anoxic and aprotic media. Through the establishment of ternary phase diagrams involving silicon-alkanes, perfluoroalkanes (PFA) and semi-fluorinated alkanes (SFA), we intend to propose a new soft-templating approach to synthesize Silicon Carbide (SiC). This approach would allow us to control the porosity of the SiC at the mesoscopic scale, and opens a perspective for elaborating monoliths.
To date, it is indeed very difficult to achieve monoliths of pure SiC (without oxide) combining exceptional mechanical and thermodynamical properties with a high specific surface area, a property of major interest for catalysis supports. Thanks to the recent progresses i) in the synthesis of silicon bearing alkane molecules of controlled Si:C (1:1) stoichiometry, ii) in the control of their polymerization and iii) in the physical chemistry of fluorinated amphiphilic molecules, it becomes possible to envision an original synthesis route towards SiC, using amphiphilic molecules of SFA in presence of PFA molecules. The molecular organisation of SiC precursors can be controlled at the mesoscopic scale by tuning the proportion of fluorinated species and the temperature. In such mesophases, precursor molecules are pre-organized around a soft template made of SFA and PFA molecules. The in situ polymerization of the SiC precursor molecules allows their organization to be conserved once the fluorinated template was washed out. A further thermal treatment under controlled atmosphere therefore results in a SiC ceramic of controlled mesoporosity.
This project associates fundamental studies (understanding the organisation of fluorinated amphiphilic molecules at the molecular scale in totally anhydrous and anoxic media) and a strong applied stake: the production of SiC with moulded shape and controlled porosity. The bottom-up approach presented in this project starts from the synthesis of organosilicon precursor molecules and amphiphilic molecules and stretches to the production of the SiC ceramic. A special emphasis will be put on the determination of ternary phase diagrams of {organo-silicon molecules / PFA / SFA} systems using X-ray scattering techniques
In evolution with regards to the activities of the Institut de Chimie Séparative de Marcoule, this transversal project gathers specialists of organic chemistry, of complex fluid physical-chemistry and of material science. In this sense, it perfectly fits the federative objectives pursued in the partner institute.