The three-dimensional structure of flexible resorcinol-formaldehyde aerogels investigated by means of holotomography

• DOI: 10.1007/s10971-017-4363-6
• Publication Date: 2017-03-27T09:12:20Z
• Authors: René Tannert; Marina Schwan; Ameya Rege; Mario Eggeler; Julio Cesar da Silva; Marion Bartsch; Barbara Milow; Mikhail Itskov; Lorenz Ratke
• Keywords: Aerogels 3D-structure Holotomography Pore-size distribution; Aerogele; Experimentelle und numerische Methoden; 02 engineering and technology; 0210 nano-technology; 01 natural sciences; 0104 chemical sciences

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.