Abstract
Organic aerogels based on resorcinol-formaldehyde gels display remarkable properties due to their pronounced nanoporosity. Therefore, studies towards the understanding of their structure-property-relationship are of high value for the design of improved materials. X-ray tomography is a technique that has been used for the structural elucidation of porous materials, but so far no highly resolved three-dimensional structures of resorcinol-formaldehyde gels have been obtained under the classical absorption-based experimental X-ray setup. This paper reports on the successful analysis of a superflexible resorcinol-formaldehyde aerogel using zoom holotomography that yielded images with an unprecedented resolution in the sub-micrometer range. The preparation of suitable powder from monolithic superflexible resorcinol-formaldehyde, the experimental conditions for tomography, and data-processing to obtain a 3D-image of the dried gel sample are described. Macropores above ca. 75 nm could be identified and visualized. They were shown to adopt almost spherical shape and to display a low connectivity. A quantitative analysis of the pore space revealed that most of the identified pores are small macropores (diameter < 0.5 µm), yet most pore volume is located in larger macropores of 1–4 µm diameter.
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Acknowledgements
The authors wish to thank Benjamin Ignatzi for the production and characterization of powders and Guillermo Requena and Galina Kasperovich for assistance and computer resources provided during preliminary image analysis. We thank the European Synchrotron Radiation Facility for access to synchrotron radiation facilities at ID16A beamline (proposal SC4154 granted to RT, MS, AR, BM, M I, and LR). Financial support from the German Aerospace Center (program “Terrestrial vehicles”, project “Next Generation Car” for RT, MS, BM, and LR) is gratefully acknowledged.
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Tannert, R., Schwan, M., Rege, A. et al. The three-dimensional structure of flexible resorcinol-formaldehyde aerogels investigated by means of holotomography. J Sol-Gel Sci Technol 84, 391–399 (2017). https://doi.org/10.1007/s10971-017-4363-6
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DOI: https://doi.org/10.1007/s10971-017-4363-6