To investigate how the multiphase structures affect the electrical conductivity in semicrystalline polymer composites, herein, an accurate multiphase content calculation method is proposed and verified, which combines amorphous phase information in broadband dielectric spectroscopy and crystalline phase information in differential scanning calorimetry. Taken aluminium hydroxide (ATH) filled silicone rubber as an example, it is found that the rigid amorphous fraction (RAF) corresponding to the chains constrained by crystals (RAF cry ) is not linearly increased with crystalline fraction (CF). Compared to non-isothermal crystallisation, RAF caused by ATH/silicone rubber interface (RAF int ) after isothermal crystallisation at 213 K changes little, while mobile amorphous fraction and RAF cry is attenuated and CF is strengthened. Based on the calculated structures of ATH filled silicone rubber, activation energy of conductivities during cooling is dominated by the thermal transition for conductive ions and shortened distance among the conductive ions through shrunk volumes of the amorphous phase. Our findings deepen the understanding of multiphase content in semi-crystalline polymer composites and its relationship with electrical conductivity, which can be applied in manipulating electrical performance of semi-crystalline polymers by fillers.
| INTRODUCTIONBy a combination of various insulating polymers and nonconductive fillers, polymer composites are endowed with improved properties, such as insulation, mechanical strength, and heat conduction [1]. Under appropriate conditions, the polymer segments with regular structure would form crystals coexisting with the amorphous phase, namely semi-crystalline polymers. Nowadays, semi-crystalline polymer with nonconductive fillers has been extensively applied in important fields, such as electric, transportation, construction etc. [2]. In the semi-crystalline polymers composites, many different phases exist, such as rigid amorphous phase caused by crystals and interfaces, mobile amorphous phase, crystalline phase, and fillers phase [1], which is important in determining the electrical property, a key property for a broad range of applications [3]. Under weak electric field, for electrical conductivity, the insulating fillers hardly provide a conductive pathway. Crystalline phase is always considered to be more insulating than amorphous phase in polymer conductivity [4,5]. According to the classical theory, ion transport, the main conductive mechanism in insulating polymers under weak electric field, is coupled to the polymer segmental motion that is various in different amorphous phase [6]. Therefore, the multiphase content and structures are closely related to the electrical properties. Understanding the multiphase information is essential to manipulating the electrical performances in semicrystalline polymers composites.