The Influence of the Gelation-Solvent on the Microstructure of Some Phenolic Aerogels

Kurzfassung

Aerogels based on phenolics, such as resorcinol-formaldehyde (RF), are receiving increasing attention due to their remarkable thermally insulating and light-weight properties that can be traced back to their unique microstructure.[1] While structure and, thus, properties of these organic aerogels are typically tuned by controlling synthetic parameters such as the monomer concentrations, temperature, type of catalyst and pH-value, the influence of the solvent on gelation is only scarcely exploited.[2] We recently developed trimethoxybenzene-formaldehyde (TMBF) aerogels as hydrophobic analogs of RF and observed significant differences in microstructural features and BET surface areas, depending on the solvent employed in polymerization.[3] To further investigate the influence of solvent on the microstructures of resulting aerogels, we have studied phenols with varying degree of alkylation in a variety of solvents. We report on the derivation of microstructures from SEM images and physisorption sotherms, their correlations with the Hansen solubility parameters of the respective solvents and propose mechanistic explanations. This work highlights the importance of the nature of the solvent for polymerizations of O-alkylated phenols enabling the tuning of the microstructural properties of these phenolic aerogels. [1] X. Lu, M. C. Arduini-Schuster, J. Kuhn, O. Nilsson, J. Fricke, R. W. Pekala, Science 1992, 255, 971-972. [2] A. M. ElKhatat, S. A. Al-Muhtaseb, Adv. Mater. 2011, 23, 2887-2903. [3] T. Anklam, C. Farès, R. Tannert, in 7th International Conference on Multifunctional, Hybrid and Nanomaterials (Eds.: M. Antonietti, C. Sanchez, R. Xu), Elsevier, Genova, Italy, 2022.