Abstract
Hierarchical biological materials, such as osteons and plant cell walls, are complex structures that are difficult to mimic. Here, we combine liquid crystal systems and polymerization techniques within confined systems to develop complex structures. A single-domain concentric chiral nematic polymeric fiber was obtained by confining cellulose nanocrystals (CNCs) and hydroxyethyl acrylate inside a capillary tube followed by UV-initiated polymerization. The concentric chiral nematic structure continues uniformly throughout the length of the fiber. The pitch of the chiral nematic structure could be controlled by changing the CNC concentration. We tracked the formation of the concentric structure over time and under different conditions with variation of the tube orientation, CNC concentration, CNC type, and capillary tube size. We show that the inner radius of the capillary tube is important and a single-domain structure was only obtained inside small-diameter tubes. At low CNC concentration, the concentric chiral nematic structure did not completely cover the cross-section of the fiber. The highly ordered structure was studied using imaging techniques and X-ray diffraction, and the mechanical properties and structure of the chiral nematic fiber were compared to a pseudo-nematic fiber. CNC polymeric fibers could become a platform for many applications from photonics to complex hierarchical materials.
Highlights
Biological materials, such as osteons and plant cell walls, have complicated hierarchical structures, with organization over many length scales.[1,2,3] Each level in the hierarchy represents an increase in organizational complexity
This study stemmed from the observation that lling a capillary tube (0.4 mm inner diameter) with 4.5 wt% cellulose nanocrystals (CNCs) solution resulted in the formation of birefringent periodic lines parallel to the length of the tube when observed between crossed polarizers using Polarized optical microscopy (POM) (Fig. 2)
The lines are evenly spaced and resemble the characteristic ngerprint lines observed in chiral nematic CNC structures using POM, where the distance between the lines is equal to one-half pitch (p/2).[26]
Summary
Biological materials, such as osteons and plant cell walls, have complicated hierarchical structures, with organization over many length scales.[1,2,3] Each level in the hierarchy represents an increase in organizational complexity. At the rst length scale, molecular- and nano-sized units co-assemble to form highly ordered micron-sized units. These micron-sized units interact in sophisticated ways to form larger structural units. This hierarchical fabrication process continues to the macroscopic scale, resulting in a material with unique properties. Mimicking the bottom-up construction of hierarchical materials at the nano/micron scale has remained elusive, but we show here that combining liquid crystals and polymerization techniques
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