Humidity is an efficient instrument for facilitating changes in local architectures of two-dimensional surfaces assembled from nanoscaled biomaterials. Here, complementary surface-sensitive methods are used to collect explicit and precise experimental evidence on the water vapor sorption into (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) oxidized cellulose nanofibril (CNF) thin film over the relative humidity (RH) range from 0 to 97%. Changes in thickness and mass of the film due to water vapor uptake are tracked using spectroscopic ellipsometry and quartz crystal microbalance with dissipation monitoring, respectively. Experimental data is evaluated by the quantitative Langmuir/Flory–Huggins/clustering model and the Brunauer–Emmett–Teller model. The isotherms coupled with the quantitative models unveil distinct regions of predominant sorption modes: specific sorption of water molecules below 10% RH, multilayer build-up between 10 to 75% RH, and clustering of water molecules above 75% RH. The study reveals the sorption mechanisms underlying the well-known water uptake behavior of TEMPO oxidized CNF directly at the gas–solid interface.

中文翻译：

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定量模型揭示的水蒸气吸附到纤维素纳米原纤维膜中的界面机制

湿度是一种有助于改变由纳米级生物材料组装而成的二维表面局部结构变化的有效工具。在这里，使用互补的表面敏感方法来收集关于水蒸气吸附到（2,2,6,6-四甲基哌啶-1-基）氧基（TEMPO）氧化纤维素纳米原纤维（CNF）薄膜上的明确而精确的实验证据。相对湿度（RH）的范围是0到97％。分别使用光谱椭圆偏振法和带有耗散监测的石英晶体微量天平跟踪由于水蒸气吸收而引起的薄膜厚度和质量变化。实验数据通过定量的Langmuir / Flory-Huggins /聚类模型和Brunauer-Emmett-Teller模型进行评估。等温线与定量模型相结合揭示了主要吸附模式的不同区域：相对湿度低于10％RH的水分子的特定吸附，相对湿度在10％至75％RH之间的多层堆积以及相对湿度75％相对于水分子的聚集。这项研究揭示了众所周知的TEMPO氧化CNF直接在气固界面处的吸水行为的吸附机理。