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Conformal Ultrathin Coating by scCO2-Mediated PMMA Deposition: A Facile Approach To Add Moisture Resistance to Lightweight Ordered Nanocellulose Aerogels
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-03-22 00:00:00 , DOI: 10.1021/acs.chemmater.7b05226 Sven F. Plappert 1 , Sakeena Quraishi 1 , Jean-Marie Nedelec 2 , Johannes Konnerth 3 , Harald Rennhofer 4 , Helga C. Lichtenegger 4 , Falk W. Liebner 1
Chemistry of Materials ( IF 7.2 ) Pub Date : 2018-03-22 00:00:00 , DOI: 10.1021/acs.chemmater.7b05226 Sven F. Plappert 1 , Sakeena Quraishi 1 , Jean-Marie Nedelec 2 , Johannes Konnerth 3 , Harald Rennhofer 4 , Helga C. Lichtenegger 4 , Falk W. Liebner 1
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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, scCO2-mediated antisolvent 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 patterns 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 (>500 m2 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° ± 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.
中文翻译：
通过scCO 2介导的PMMA沉积形成的共形超薄涂层：一种为轻型有序纳米纤维素气凝胶增加耐湿性的简便方法
提出了一种在各向异性气凝胶结构完全保留的情况下，向由个性化纤维素纳米纤维（i- CNF）组成的透明向列型气凝胶增加耐湿性的简便方法。应用顺序的氮氧化物介导的氧化和机械纤维素纤维分层，以获得i- CNF在水中的分散体。由i -CNF表面羧酸酯基团之间的排斥力引起的向列有序分别通过酸诱导的氢键和凝胶化来设定。溶剂交换成丙酮，用PMMA浸渍，scCO 2介导的次级聚合物的反溶剂沉淀，以及scCO 2间质丙酮的萃取提供了高度疏水的纳米复合气凝胶。利用偏振光和Michel–Levy图表进行双折射研究以评估干涉图样，表明向列型i -CNF的排列实际上不受相应的表面改性和scCO 2干燥步骤的影响。形态学研究表明，混合气凝胶的大内表面（> 500 m 2 g –1）由均质的超薄PMMA（单）层组成，几乎不影响高孔隙率（≥99％）和透明度（> 77 i固有的％透射率，600 nm，2.13 mm厚度-CNF气凝胶。从高的水接触角（119.4°±7.5）可以明显看出，所获得的材料表现出优异的耐湿性。由于PMMA赋予气凝胶刚度和疏水性，即使在低至9.6 mg cm –3的超低密度下，也可以避免在潮湿环境或真空条件下纳米纤维的聚集。
更新日期：2018-03-22
中文翻译：
通过scCO 2介导的PMMA沉积形成的共形超薄涂层：一种为轻型有序纳米纤维素气凝胶增加耐湿性的简便方法
提出了一种在各向异性气凝胶结构完全保留的情况下，向由个性化纤维素纳米纤维（i- CNF）组成的透明向列型气凝胶增加耐湿性的简便方法。应用顺序的氮氧化物介导的氧化和机械纤维素纤维分层，以获得i- CNF在水中的分散体。由i -CNF表面羧酸酯基团之间的排斥力引起的向列有序分别通过酸诱导的氢键和凝胶化来设定。溶剂交换成丙酮，用PMMA浸渍，scCO 2介导的次级聚合物的反溶剂沉淀，以及scCO 2间质丙酮的萃取提供了高度疏水的纳米复合气凝胶。利用偏振光和Michel–Levy图表进行双折射研究以评估干涉图样，表明向列型i -CNF的排列实际上不受相应的表面改性和scCO 2干燥步骤的影响。形态学研究表明，混合气凝胶的大内表面（> 500 m 2 g –1）由均质的超薄PMMA（单）层组成，几乎不影响高孔隙率（≥99％）和透明度（> 77 i固有的％透射率，600 nm，2.13 mm厚度-CNF气凝胶。从高的水接触角（119.4°±7.5）可以明显看出，所获得的材料表现出优异的耐湿性。由于PMMA赋予气凝胶刚度和疏水性，即使在低至9.6 mg cm –3的超低密度下，也可以避免在潮湿环境或真空条件下纳米纤维的聚集。
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