Effects of liquid crystalline and shear alignment on the optical properties of cellulose nanocrystal films

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• 作者：Alexander D. Haywood ; Virginia A. Davis
• 关键词：Cellulose nanocrystal ; Rheo ; optics ; Liquid crystal ; Thin film ; Aligned films
• 刊名：Cellulose
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：24
• 期：2
• 页码：705-716
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Bioorganic Chemistry; Physical Chemistry; Organic Chemistry; Polymer Sciences;
• 出版者：Springer Netherlands
• ISSN：1572-882X
• 卷排序：24

文摘

Rheo-optics, microspectrophotometry, and optical contrast measurements were used to gain new insights into the interrelated effects of liquid crystalline phase behavior, flow alignment, and microstructural relaxation on cellulose nanocrystal (CNC) films’ alignment and optical properties. Optical contrast measurements were found to be an effective and facile way of determining changes in anisotropy directly from cross-polarized microscopy images. This method was used to continuously measure microstructural relaxation after the cessation of shear as well as the anisotropy of dried CNC films. Aqueous liquid crystalline CNC dispersions showed greater alignment after shear than isotropic or biphasic dispersions. However, CNC gels exhibited lower alignment at equivalent shear rates. The combination of greater initial alignment and slower relaxation of sheared liquid crystalline dispersions resulted in the most optically anisotropic films. Depending on their thickness, the CNC films were optically transparent in the visible regime or exhibited tunable interference colors. The results of this work highlight the tunability of CNC dispersion processing for producing color filters and other optical materials with controlled properties.