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Research Mesini

Self-assembled nanotubes

We have developed a series of aromatic diamide organogelators (Fig 1). We study the structure of the gels formed from those compounds at the microscopic level with the techniques mastered in our group, especially freeze fracture TEM and small angle scattering [1]. The goal of these studies is to identify the molecular parameters that govern their self-assembly ; synthesis of analogues has been used to modify these parameters in order to control shapes and dimensions. The approach has successfully give different shapes : lamellae, ribbons and even nanotubes, within the same compound family.

Figure 1 : Left Structure of the series BHPBn. The length of the ester chain allows the control of the shape of the self-assembly. For instance n = 10 gives nanotubes (see figure below). Right : self assembled nanotube of diamide BHPB10. Freeze fracture-TEM

The most striking example is BHPB-10 that forms nanotubes of 30 nm diameters and several µm lengths in apolar solvents (Fig. 1) [2]. Lately, we have used those nanoobjects as templates to form large mesopores in organic resins by a “molding” process [3] : the tubes are formed in a monomer/crosslinkers mixture, which yields as a first step, a thermoreversible gel. Photopolymerization of this gel yields a resin containing the nanotubes. When the nanotubes are leached out with a dissociating solvent, they leave cylindrical pores (Fig. 2).

Figure 2 : Strategy used to form mesoporous resins from self-assembled nanotubes.

The morphology and size of the pores correspond closely to those of the template tubes, as shown by TEM and porosimetry (Fig. 3 Left). The same strategy has been also successful to form helical pores in resins (Fig.3 Right).Basic treatment of the mesoporous resin can be used to functionalize the pores and synthesize that were tested as catalysts for a model reaction[4].Theyshowed an activity similar the one of alkaline-substituted mesoporous silica.

Figure 3 :TEM of microsections of imprinted resins : Left : mesoporous resin synthesized with BHPB10 as a template. Right : Helical mésopores obtained with helical tapes as templates.

We have been also able to derivatize those tubes on their surface without altering the tubular structure, to make them reactive by click reactions [5]. The tubes remained self-assembled even though the final molecules would not spontaneously re-assemble into nonotubes. This allows, through supercritical drying, to fabricate reactive aerogel that are also good candidates for catalyst supports.

[1] Schmidt, R. ; Schmutz, M. ; Mathis, A. ; Decher, G. ; Rawiso, M. ; Mesini, P. J., Langmuir 2002,18, 7167-7173.
[2] Diaz, N. ; Simon, F. X. ; Schmutz, M. ; Rawiso, M. ; Decher, G. ; Jestin, J. ; Mésini, P. J., Angew. Chem., Int. Ed. Engl. 2005,44, 3260-3264.
[3] Simon, F. X. ; Khelfallah, N. S. ; Schmutz, M. ; Diaz, N. ; Mesini, P. J., J. Am. Chem. Soc. 2007,129, 3788-3789.
[4] Nguyen, T.-T.-T. ; Simon, F.-X. ; Khelfallah, N. S. ; Schmutz, M. ; Mesini, P. J., J. Mater. Chem. 2010, 20, 3831-3833.
[5] Nguyen, T.-T.-T. ; Simon, F.-X. ; Schmutz, M. ; Mésini, P. J., Chem. Commun. 2009, 3457-3459.

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