Tung Wei-Shao, Composto Russell J, Clarke Nigel, Winey Karen I
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia 19104-6272, United States.
Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom.
ACS Macro Lett. 2015 Sep 15;4(9):916-920. doi: 10.1021/acsmacrolett.5b00256. Epub 2015 Aug 13.
Polymer radii of gyration in isotropic single-walled carbon nanotube (SWCNT)/polymer nanocomposites were previously found to increase with increasing SWCNT concentration. Here, the SWCNTs in nanocomposites were aligned by melt fiber spinning, and the polymer chain conformations were found to be anisotropic. Using SAXS and SANS, the anisotropic SWCNT meshes were found to have smaller mesh sizes in the direction perpendicular to the alignment direction than along the alignment direction. At fixed SWCNT orientation, the radius of gyration was probed parallel and perpendicular to the alignment direction, and , respectively, using SANS. With increasing SWCNT concentration, increases significantly more than , such that the extent of anisotropy increases with SWCNT concentration. The anisotropic polymer conformation is larger in the direction perpendicular to the alignment direction, which corresponds to a smaller SWCNT mesh size. Thus, when the SWCNT concentration and alignment combine to produce a SWCNT mesh size that is smaller than the unperturbed , the polymer conformation circumvents the SWCNTs by adopting a larger . Changes in the polymer conformation in nanocomposites with rod-like nanoparticles has important ramifications for entanglement density, polymer dynamics, and mechanical properties.
先前发现，各向同性单壁碳纳米管（SWCNT）/聚合物纳米复合材料中的聚合物回转半径会随着SWCNT浓度的增加而增大。在此，通过熔体纺丝使纳米复合材料中的SWCNT排列整齐，发现聚合物链构象具有各向异性。利用小角X射线散射（SAXS）和小角中子散射（SANS）发现，各向异性的SWCNT网格在垂直于排列方向的方向上的网格尺寸比沿排列方向的要小。在固定的SWCNT取向下，分别使用SANS在平行和垂直于排列方向上探测回转半径 和 。随着SWCNT浓度的增加， 的增加幅度明显大于 ，使得各向异性程度随SWCNT浓度增加。在垂直于排列方向上，各向异性聚合物构象更大，这对应于更小的SWCNT网格尺寸。因此，当SWCNT浓度和排列共同作用产生的SWCNT网格尺寸小于无扰 时，聚合物构象通过采用更大的 来避开SWCNT。具有棒状纳米粒子的纳米复合材料中聚合物构象的变化对缠结密度、聚合物动力学和机械性能具有重要影响。
