Fry D, Langhorst B, Wang H, Becker M L, Bauer B J, Grulke E A, Hobbie E K
National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Chem Phys. 2006 Feb 7;124(5):054703. doi: 10.1063/1.2159488.
We use a polarization-modulation technique to investigate the optical anisotropy of multi- and single-wall carbon nanotubes suspended in a variety of solvents under simple shear flow. Measurements of birefringence and dichroism are performed as a function of shear rate, tube concentration, and solvent viscosity. At fixed volume fraction, the anisotropy increases with increasing shear stress due to enhanced flow alignment. At fixed shear stress, the anisotropy increases with volume fraction due to rotational excluded-volume interactions. By considering the rotational diffusivity as a function of nanotube length, diameter, concentration, and solvent viscosity, we demonstrate a leading-order scaling relation for the optical anisotropy in terms of rotary Peclet number Pe. At low Pe, our results are in qualitative agreement with the theoretical predictions of Doi and Edwards. At high Pe, our data suggest that the degree of nanotube alignment scales as Pe16.
我们采用偏振调制技术来研究在简单剪切流作用下悬浮于多种溶剂中的多壁和单壁碳纳米管的光学各向异性。双折射和二向色性的测量是作为剪切速率、管浓度和溶剂粘度的函数来进行的。在固定体积分数下，由于流动排列增强，各向异性随剪切应力的增加而增大。在固定剪切应力下，由于旋转排除体积相互作用，各向异性随体积分数增加。通过将旋转扩散率视为纳米管长度、直径、浓度和溶剂粘度的函数，我们证明了光学各向异性关于旋转佩克莱数Pe的主导阶标度关系。在低Pe时，我们的结果与Doi和Edwards的理论预测在定性上一致。在高Pe时，我们的数据表明纳米管排列程度按Pe16标度。
