Alignment of Liquid-Crystalline Polymers by Field-Oriented, Carbon Nanotube Directors

Abstract

Bulk liquid-crystalline polymer (LCP) material can be macroscopically aligned by seeding the growth of LCP domains with preoriented, single-wall carbon nanotubes (SWNTs). SWNT seeds dispersed in a columnar polyoxazoline melt were first oriented by applying an ac electric field across the molten material. Then, cooling the material below the liquid-crystalline transition temperature yielded domains that were oriented in the direction of the applied field. The orientation of these domains was characterized by temperature-controlled polarized light microscopy, static birefringence, and wide-angle X-ray scattering. These experiments demonstrate that domains can be oriented at field strengths that are orders of magnitude lower than those used to pole anisotropic polymers alone, and that the seeded domains can grow together to form homogeneously oriented bulk material. Because the nanotubes act only as nucleants, very little SWNT material is required. We anticipate that this general concept could aid the fabrication of monolithic objects with tailored anisotropic properties from SWNT−polymer composites.