Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849, USA.
Soft Matter. 2017 Nov 22;13(45):8451-8462. doi: 10.1039/c7sm00685c.
Cellulose nanocrystals (CNC) have been studied as nanostructured building blocks for functional materials and function as a model nanomaterial mesogen for cholesteric (chiral nematic) liquid crystalline phases. In this study, both rheology and small angle neutron scattering (RheoSANS) were used to measure changes in flow-oriented order parameter and viscosity as a function of shear rate for isotropic, biphasic, liquid crystalline, and gel dispersions of CNC in deuterium oxide (DO). In contrast to plots of viscosity versus shear rate, the order parameter trends showed three distinct rheological regions over a range of concentrations. This finding is significant because the existence of three rheological regions as a function of shear rate is a long-standing signature of liquid crystalline phases composed of rod-like polymers, but observing this trend has been elusive for high-concentration dispersions of anisotropic nanomaterials. The results of this work are valuable for guiding the development of processing methodologies for producing ordered materials from CNC dispersions and the broader class of chiral nanomaterial mesogens.
纤维素纳米晶体 (CNC) 已被研究为功能材料的纳米结构构建块，并作为胆甾型 (手性向列) 液晶相的模型纳米材料介晶。在这项研究中，流变学和小角中子散射 (RheoSANS) 都被用于测量各向同性、双相、液晶和 CNC 在重水中的凝胶分散体的流动取向有序参数和粘度随剪切率的变化。与粘度与剪切率的关系图相比，有序参数趋势在一系列浓度范围内显示出三个明显的流变区域。这一发现意义重大，因为作为剪切率函数的三个流变区域的存在是由棒状聚合物组成的液晶相的一个长期特征，但对于各向异性纳米材料的高浓度分散体，观察到这一趋势一直很困难。这项工作的结果对于指导从 CNC 分散体和更广泛的手性纳米材料介晶类中制备有序材料的加工方法的发展具有重要价值。
