Strain Hardening and Pore Size Harmonization by Uniaxial Densification: A Facile Approach toward Superinsulating Aerogels from Nematic Nanofibrillated 2,3-Dicarboxyl Cellulose

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Strain Hardening and Pore Size Harmonization by Uniaxial Densification: A Facile Approach toward Superinsulating Aerogels from Nematic Nanofibrillated 2,3-Dicarboxyl Cellulose

Sven F. Plappert, Jean-Marie Nedelec, Helga C. Lichtenegger, Harald Rennhofer, Falk W. Liebner

Dissolving pulp has been subjected to consecutive periodate/chlorite treatments to afford 2,3-dicarboxyl cellulose (DCC, 1.02 mmol g^–1 COOH). Subsequent nanofibrillation afforded stable nematic nf-DCC dispersions (average particle size 2.1 nm × 525 nm) at significantly lower energy input compared to TEMPO-oxidation. Acid-induced gelation triggered by extensive hydrogen bonding sets the ordered state and affords free-standing hydrogels that can be converted to highly transparent birefringent aerogels by scCO₂ drying. Uniaxial compression of the obtained ultra-lightweight ductile nf-DCC aerogels down to 5% of their original volume intriguingly preserves nematic orientation and transparence. Simultaneously, strain hardening translates into exceptionally good mechanical properties, such as toughness at nearly zero Poisson’s ratio. Uniaxial compression has been furthermore demonstrated to be a facile and efficient means for converting nf-DCC aerogels of broad, multiscale pore size distribution into entirely micro/mesoporous scaffolds of narrow size distribution at far-reaching preservation of porosity. Following this approach, thermally superinsulating nf-DCC aerogels (λ = 0.018 W m^–1 K^–1) have been prepared, whose intriguing mechanical properties, transparence, and nematic ordering bear great potential for other applications as well.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b00787

DOI: 10.1021/acs.chemmater.7b00787