Outstanding optical and mechanical properties can be obtained from hierarchical assemblies of nanoparticles. Herein, the formation of helically ordered, chiral nematic films obtained from aqueous suspensions of cellulose nanocrystals (CNCs) were studied as a function of the initial suspension state. Specifically, nanoparticle organization and the structural colors displayed by the resultant dry films were investigated as a function of the anisotropic volume fraction (AVF), which depended on the initial CNC concentration and equilibration time. The development of structural color and the extent of macroscopic stratification were studied by optical and scanning electron microscopy as well as UV-vis spectroscopy. Overall, suspensions above the critical threshold required for formation of liquid crystals resulted in CNC films assembled with longer ranged order, more homogeneous pitches along the cross sections, and narrower specific absorption bands. This effect was more pronounced for the suspensions that were closer to equilibrium prior to drying. Thus, we show that high AVF and more extensive phase separation in CNC suspensions resulted in large, long-range ordered chiral nematic domains in dried films. Additionally, the average CNC aspect ratio and size distribution in the two separated phases were measured and correlated to the formation of structured domains in the dried assemblies.

中文翻译：

---

纤维素纳米晶体悬浮液的各向异性对分层、域结构形成和结构颜色的影响。

纳米颗粒的分层组装可以获得出色的光学和机械性能。在此，研究了从纤维素纳米晶体（CNC）的水悬浮液中获得的螺旋有序、手性向列膜的形成作为初始悬浮状态的函数。具体来说，研究了所得干膜显示的纳米颗粒组织和结构颜色作为各向异性体积分数 (AVF) 的函数，这取决于初始 CNC 浓度和平衡时间。通过光学和扫描电子显微镜以及紫外可见光谱研究了结构色的发展和宏观分层的程度。总体而言，悬浮液高于形成液晶所需的临界阈值，导致组装的 CNC 薄膜具有更长的有序范围、沿横截面的节距更均匀以及更窄的比吸收带。对于干燥前更接近平衡的悬浮液，这种效果更为明显。因此，我们表明 CNC 悬浮液中的高 AVF 和更广泛的相分离导致干燥薄膜中产生大的、长程有序的手性向列域。此外，还测量了两个分离相的平均 CNC 纵横比和尺寸分布，并将其与干燥组件中结构化域的形成相关联。