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Nano-to-meso structure of cellulose nanocrystal phases in ethylene-glycol-water mixtures.
Soft Matter ( IF 3.4 ) Pub Date : 2020-07-28 , DOI: 10.1039/d0sm01025a
David Attia 1 , Neta Cohen 1 , Guy Ochbaum 1 , Yael Levi-Kalisman 2 , Ronit Bitton 3 , Rachel Yerushalmi-Rozen 3
Affiliation  

The self-assembly and phase behavior of cellulose nanocrystals (CNCs) in binary liquid mixtures of ethylene-glycol (EG):water was investigated. Our findings indicate that a small fraction of water delays the onset of colloidal jammed states previously reported in water-free organic solvents. Here the full phase diagram of CNCs evolves, including the chiral nematic phase (N*), characterized by long-range orientational order and non-isotropic macroscopic properties. Furthermore, the effect of the solvent-mixture composition on the properties of the CNC mesophases is found to be scale-dependent: the micron-size pitch of the N* phase decreases as the dielectric constant (εr) of the solvent mixture is reduced (higher EG content). Yet the nanometric inter-particle spacing of the CNC rods (measured using SAXS and cryo-TEM) is almost independent on the EG content. Also, unlike theoretical predictions, the transition to the biphasic regime is not sensitive to εr of the solvent mixtures and takes place at a higher CNC volume fraction than in aqueous suspensions. These observations may be rationalized by hypothesizing that vicinal water, adsorbed at the CNC surface, prevents kinetic arrest, and dictates the local dielectric constant and thus the effective diameter of the rods (via the Debye length), while εr of the liquid-mixture dominates the pitch length (micron scale) and the optical properties. These findings indicate that the water content of EG:water mixtures may be used for engineering colloidal inks where delayed kinetic arrest and jamming of the CNCs enable printing and casting of tunable, optically-active thin films and coatings.

中文翻译:

乙二醇-乙二醇-水混合物中纤维素纳米晶相的纳米-介观结构。

研究了乙二醇(EG):水的二元混合液中纤维素纳米晶体(CNC)的自组装和相行为。我们的发现表明,一小部分水会延迟以前在无水有机溶剂中报道的胶体堵塞状态的发生。在这里,CNC的完整相图得到了发展,包括手性向列相(N *),其特征在于长距离取向顺序和非各向同性的宏观特性。此外,在中间相CNC的属性溶剂混合物组合物的效果被发现是比例相关:所述N *相随着所述介电常数(的微米尺寸的间距ε - [R)的混合溶剂减少(较高的EG含量)。然而,CNC棒的纳米粒子间间距(使用SAXS和cryo-TEM测量)几乎与EG含量无关。此外,与理论预测,到该双相体系的过渡是不敏感ε - [R的溶剂混合物和发生在更高的CNC体积分数比在水性悬浮液。这些观察结果可通过假设到该连位水,吸附在CNC表面,防止动力学逮捕,和指令本地介电常数并由此有效直径的杆(合理化通过德拜长度),而ε - [R液体混合物的量占主导地位的节距长度(微米级)和光学性能。这些发现表明,EG:水混合物的水含量可用于工程胶体油墨,其中CNC的延迟动力学停滞和堵塞使印刷和浇铸可调光学活性薄膜和涂层成为可能。
更新日期:2020-09-23
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