Aulin Christian, Ahola Susanna, Josefsson Peter, Nishino Takashi, Hirose Yasuo, Osterberg Monika, Wågberg Lars
Fibre Technology, Royal Institute of Technology, Teknikringen 56, 100 44 Stockholm, Sweden.
Langmuir. 2009 Jul 7;25(13):7675-85. doi: 10.1021/la900323n.
A systematic study of the degree of molecular ordering and swelling of different nanocellulose model films has been conducted. Crystalline cellulose II surfaces were prepared by spin-coating of the precursor cellulose solutions onto oxidized silicon wafers before regeneration in water or by using the Langmuir-Schaefer (LS) technique. Amorphous cellulose films were also prepared by spin-coating of a precursor cellulose solution onto oxidized silicon wafers. Crystalline cellulose I surfaces were prepared by spin-coating wafers with aqueous suspensions of sulfate-stabilized cellulose I nanocrystals and low-charged microfibrillated cellulose (LC-MFC). In addition, a dispersion of high-charged MFC was used for the buildup of polyelectrolyte multilayers with polyetheyleneimine on silica with the aid of the layer-by-layer (LbL) technique. These preparation methods produced smooth thin films on the nanometer scale suitable for X-ray diffraction and swelling measurements. The surface morphology and thickness of the cellulose films were characterized in detail by atomic force microscopy (AFM) and ellipsometry measurements, respectively. To determine the surface energy of the cellulose surfaces, that is, their ability to engage in different interactions with different materials, they were characterized through contact angle measurements against water, glycerol, and methylene iodide. Small incidence angle X-ray diffraction revealed that the nanocrystal and MFC films exhibited a cellulose I crystal structure and that the films prepared from N-methylmorpholine-N-oxide (NMMO), LiCl/DMAc solutions, using the LS technique, possessed a cellulose II structure. The degree of crystalline ordering was highest in the nanocrystal films (approximately 87%), whereas the MFC, NMMO, and LS films exhibited a degree of crystallinity of about 60%. The N,N-dimethylacetamide (DMAc)/LiCl film possessed very low crystalline ordering (<15%). It was also established that the films had different mesostructures, that is, structures around 10 nm, depending on the preparation conditions. The LS and LiCl/DMAc films are smooth without any clear mesostructure, whereas the other films have a clear mesostructure in which the dimensions are dependent on the size of the nanocrystals, fibrillar cellulose, and electrostatic charge of the MFC. The swelling of the films was studied using a quartz crystal microbalance with dissipation. To understand the swelling properties of the films, it was necessary to consider both the difference in crystalline ordering and the difference in mesostructure of the films.
对不同纳米纤维素模型薄膜的分子有序度和溶胀程度进行了系统研究。通过将前体纤维素溶液旋涂到氧化硅晶片上，然后在水中再生，或者使用朗缪尔-谢弗（LS）技术来制备结晶纤维素II表面。无定形纤维素薄膜也通过将前体纤维素溶液旋涂到氧化硅晶片上制备。通过将硫酸根稳定的纤维素I纳米晶体和低电荷微纤化纤维素（LC-MFC）的水悬浮液旋涂到晶片上来制备结晶纤维素I表面。此外，借助层层（LbL）技术，使用高电荷MFC的分散体与聚乙烯亚胺在二氧化硅上构建聚电解质多层膜。这些制备方法在纳米尺度上产生了适合X射线衍射和溶胀测量的光滑薄膜。分别通过原子力显微镜（AFM）和椭偏测量详细表征了纤维素薄膜的表面形态和厚度。为了确定纤维素表面的表面能，即它们与不同材料进行不同相互作用的能力，通过测量与水、甘油和二碘甲烷的接触角对其进行了表征。小入射角X射线衍射表明，纳米晶体和MFC薄膜呈现纤维素I晶体结构，而使用LS技术由N-甲基吗啉-N-氧化物（NMMO）、LiCl/DMAc溶液制备的薄膜具有纤维素II结构。纳米晶体薄膜中的结晶有序度最高（约87%），而MFC、NMMO和LS薄膜的结晶度约为60%。N，N-二甲基乙酰胺（DMAc）/LiCl薄膜的结晶有序度非常低（<15%）。还确定了薄膜具有不同的介观结构，即尺寸约为10nm的结构，这取决于制备条件。LS和LiCl/DMAc薄膜很光滑，没有任何明显的介观结构，而其他薄膜具有明显的介观结构，其尺寸取决于纳米晶体、纤维状纤维素的大小以及MFC 的静电荷。使用带有耗散的石英晶体微天平研究了薄膜的溶胀。为了理解薄膜的溶胀特性，有必要同时考虑薄膜结晶有序度的差异和介观结构的差异。
