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 was 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, scCO2-mediated anti-solvent precipitation of the secondary polymer and scCO2 extraction of interstitial acetone afforded highly hydrophobic nanocomposite aerogels. Birefringence studies utilizing polarized light and the Michel-Levy Chart to evaluate interference pattern revealed that nematic i-CNF ordering is virtually not affected by the respective surface modification and scCO2 drying steps. Morphological studies provide evidence that the large internal surface (&gt; 500 m2 g-1) of the hybrid aerogels consists of a homogeneous ultrathin PMMA (mono)layer that does virtually not affect the high porosity (≥ 99 %) and transparency (&gt; 77 % transmission, 600 nm, 2.13 mm thickness) inherent to i-CNF aerogels. The obtained materials exhibited excellent resistance towards moisture as apparent from the high water contact angle (119.4° ± 7.5). As PMMA imparts the aerogels stiffness and hydrophobicity, aggregation of nanofibrils in moist environment or under vacuum conditions can be avoided even at ultra-low densities as low as 9.6 mg cm-3.

Imparting moisture resistance to transparent nematic i-CNF aerogels by scCO2-antisolvent coating of the interior with ultrathin PMMA layers

255th National Meeting (2018)

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