pH值对纤维素纳米晶液晶形态及流变性能的影响

Effects of pH on the morphology and rheological properties of cellulose nanocrystal-based liquid crystals

为研究纤维素纳米晶(CNC)悬浮液在不同pH值及质量分数下的相变行为,使用偏光显微镜确定CNC液晶相的形态特征,获得了CNC形成向列相、胆甾相和双折射玻璃相的相图。通过稳态剪切和大幅振荡剪切测定了CNC体系的流变学性质,并利用傅里叶流变学分析体系流变行为与其微观结构演变之间的关系。结果表明,添加酸或碱能屏蔽CNC间的静电排斥作用,提高体系的凝胶化作用和非线性黏弹性,从而使向列相与胆甾相区域表现出明显的下降趋势。

Effects of pH and concentration on the phase transition behavior of cellulose nanocrystal(CNC)suspensions were studied,and the morphological characteristics of the CNC liquid crystal phase were observed by polarizing microscopy.Moreover,the phase diagram of the nematic phase,cholesteric phase,and birefringence glass phase formed by CNC was obtained.The rheological properties of the CNC systems were measured by steady-state shear and large amplitude oscillatory shear.The relationship between system rheological behavior and microstructure evolution was analyzed using Fourier rheology.The result shows that the addition of acid or alkali can shield the electrostatic repulsion between the CNCs,which induces gelation and increasing the nonlinear viscoelasticity of the system.As a result,the range of the nematic phase and cholesteric phase decreases.