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Selected Publication:

Plappert, SF; Quraishi, S; Nedelec, JM; Konnerth, J; Rennhofer, H; Lichtenegger, HC; Liebner, FW.
(2018): Conformal Ultrathin Coating by scCO(2)-Mediated PMMA Deposition: A Facile Approach To Add Moisture Resistance to Lightweight Ordered Nanocellulose Aerogels
CHEM MATER. 2018; 30(7): 2322-2330. FullText FullText_BOKU

A facile approach for adding moisture resistance to transparent nematic aerogels composed of individualized cellulose nanofibers (i-CNF) at full preservation of the anisotropic aerogel structure is presented. Sequential nitroxide-mediated oxidation and mechanical cellulose fiber delamination were applied to obtain i-CNF dispersions in water. Nematic ordering caused by repulsive forces between i-CNF surface carboxylate groups was set by acid-induced hydrogen bonding and gelation, respectively. Solvent exchange to acetone, impregnation with the PMMA, scCO(2)-mediated antisolvent precipitation of the secondary polymer, and scCO(2) extraction of interstitial acetone afforded highly hydrophobic nanocomposite aerogels. Birefringence studies utilizing polarized light and the Michel-Levy Chart to evaluate interference patterns revealed that nematic i-CNF ordering is virtually not affected by the respective surface modification and scCO(2) drying steps. Morphological studies provide evidence that the large internal surface (>500 m(2) g(-1)) of the hybrid aerogels consists of a homogeneous ultrathin PMMA (mono)layer that virtually does not affect the high porosity (>= 99%) and transparency (>77% transmission, 600 nm, 2.13 mm thickness) inherent to i-CNF aerogels. The obtained materials exhibited excellent resistance toward moisture as apparent from the high water contact angle (119.4 degrees +/- 7.5). As PMMA imparts the aerogel stiffness and hydrophobicity, aggregation of nanofibrils in moist environment or under vacuum conditions can be avoided even at ultralow densities as low as 9.6 mg cm(-3).
Authors BOKU Wien:
Konnerth Johannes
Lichtenegger Helga
Liebner Falk
Plappert Sven
Quraishi Sakeena
Rennhofer Harald
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