Magnetic Orientation of Polymer Fibers in Suspension
Magnetic Orientation of Polymer Fibers in Suspension
复制标题
悬浮液中聚合物纤维的磁取向
作者：
Tsunehisa Kimura;M. Yamato;Wataru Koshimizu;and Minako Koike;T. Kawai
具有磁各向异性的抗磁性材料具有在磁场中排列的潜在能力。1液晶和液晶聚合物的磁取向是众所周知的。此外，聚乙烯单晶，2碳纤维，3，4和生物材料1，2，5的磁取向已被报道。此外，最近的研究表明，磁性取向发生在有机材料6和蛋白质7，8从溶液中结晶，在结晶聚合物的熔融结晶的诱导期，9-12和在琼脂糖凝胶的凝胶化过程中。13还报道了具有剩余磁各向异性的熔融态无机顺磁性材料的磁取向。14宏观取向由于有序域在周围粘性介质施加的流体动力扭矩的阻力下旋转而发生。为了模拟这种取向动力学，已经采用了通过磁转矩和流体动力学转矩之间的平衡导出的运动方程，15，16其中对准域通常被隐含地视为球体。然而，在某些情况下，如纤维，排列域的形状是远离一个球体，因此该方程无法描述的现象。事实上，悬浮碳纤维的排列速率对纤维长度的依赖性4不能用简单的球体模型来解释。本文提出了一个修正的运动方程。纤维的形状近似与一个长椭球体，并被认为是明确的流体动力扭矩的纵横比的依赖。该方程的解给出了作为纵横比的函数的对准速率。本文根据本文提出的修正运动方程，讨论了取向率随光纤长度变化的实验观测。
Diamagnetic materials with magnetic anisotropy have a potential ability to align in magnetic fields. 1 Magnetic orientation of liquid crystals and liquid crystalline polymers is well-known. Also, the magnetic orientation of a polyethylene single crystal, 2 carbon fibers, 3, 4 and biological materials1, 2, 5 has been reported. In addition, recent studies have revealed that the magnetic orientation occurs during the crystallization of organic materials6 and proteins7, 8 from solutions, during the induction period of the melt crystallization of crystalline polymers, 9-12 and during the gelation process of an aggarose gel. 13 Magnetic orientation of inorganic paramagnetic materials in molten states with residual magnetic anisotropy has been also reported. 14 Macroscopic orientation occurs due to the rotation of ordered domains under the resistance of the hydrodynamic torque exerted by the surrounding viscous medium. To model this orientation kinetics, an equation of motion derived through the balance between the magnetic torque and the hydrodynamic torque has been employed, 15, 16 where the aligning domain is usually regarded as a sphere implicitly. However, in some cases, such as fibers, the shape of the aligning domain is far from a sphere, and hence the equation fails to describe the phenomenon. As a matter of fact, the fiber-length dependence of the alignment rate reported for carbon fibers in suspension4 cannot be explained in terms of a simple sphere model. In this Note, a modified equation of motion is presented. The shape of a fiber is approximated with a prolate ellipsoid, and the aspect ratio dependence of the hydrodynamic torque is considered explicitly. The solution of the equation gives the alignment rate as a function of the aspect ratio. The experimental observation of the fiberlength dependence of the alignment rate is discussed on the basis of the modified equation of motion presented in this Note.