Dielectric analysis of the breakup of liquid crystalline polymer fibers in a thermoplastic matrix

In this paper we discuss the use of dielectric spectroscopy as a means to study the morphology of polymer blends. We have investigated a model system of thermotropic liquid crystalline polymer (Vectra B950) fibers lined up in a polypropylene (Stamylan P 13E10) matrix. The appearance of interfacial polarization at the interface between the two polymeric phases makes it possible to calculate the shape of the inclusions. For this purpose a formula is derived, which gives the shape factor of a distorted fiber as a function of the distortion amplitude. The calculated shapes of the fibers agree very well with the actual shapes, despite the approximations made. The agreement was proven by performing dielectric measurements under an optical microscope. As expected, the growth rate of thick fibers is smaller than that of thinner ones. A comparison between experiments under the microscope and in a dielectric sample holder showed the importance of the heating rate on the breakup of the fibers.