Preparation And Properties Of PVDF-based Thermal And Electrical Conductive Composites

Thermally and electrically conductive polyvinylidene fluoride(PVDF)composites were fabricated by the solution method,where the distribution of filler particles in the matrix was regulated via designated strategy.Several conclusions can be drawn as listed below.Fe/PVDF composites were firstly treated under external magnetic field during the solid-liquid conversion process.Thus,Fe particles could form arrangement along the magnetic induction line in the PVDF solution.This designated strategy changed the distribution state of Fe particles in the PVDF matrix and reduced the thermal conductivity threshold of composites from 20 vol.%to 5 vol.%.As Fe content reached 30 vol.%,the Fe/PVDF composites had higher thermal conductivity after magnetic treatment.Meanwhile,the electrical conductivity threshold of the composites fell from 25 vol.%to 7 vol.%.In this paper,a simple silver mirror reaction was used to prepare the CNT/PVDF composites in which CNT were coated with dense silver(Ag)layer.The purposeful distribution of Ag particles was beneficial for the formation of conductive and interconnected network.Therefore,the thermal conductivity of the CNT/PVDF composites could be improved significantly.In addition,this network possessed good electrically conductive performance without CNT.Specifically,the conductivity of PVDF@Ag composites reached 0.05 S/m.To further explore the comprehensive properties and internal structure of PVDF composites,the non-isothermal crystallization properties,crystalline composition and rheological properties of Fe/PVDF,CNT/PVDF and Ag/PVDF composites were studied.Several conclusions can be drawn as listed below.Fe particles and CNT share similar effects on the non-isothermal crystallization of PVDF matrix.Filler provided the crystallization site which could speed up the crystallization rate of the matrix.The effect became more intense under proper filler incorporation.However,the presence of filler would also hinder the motion of macromolecular chains,which prevents the PVDF matrix from completing the whole crystallization process.As a result,the crystallization enthalpy and absolute crystallinity of the PVDF matrix would be reduced.On the other hand,the cooling rate of the non-isothermal crystallization process was also an important factor affecting the crystallization behavior of PVDF composites.Under rapid cooling rate,PVDF composites shown higher crystallization rate.However,the crystallinity of the PVDF matrix would be reduced to a certain extent due to reduced crystallization time.Moreover,the motion of molecular chains had time dependence.Therefore,faster cooling rate resulted in lower crystallization temperature and larger crystallization temperature range.XRD data demonstrated that the new diffraction peak of PVDF appeared at 20.6° due to solution method,which corresponded to the ?-PVDF crystal shape,while the diffraction peak corresponding to a-PVDF was weakened.After the incorporation of the iron powder,the diffraction peak of a-PVDF was reappeared at 19.9°.With increasing iron content,the ?-PVDF diffraction peak at about 40° disappeared,and the intensity of other diffraction peaks decreased.In summary,the addition of iron powder could promote the growth of ?-PVDF to a certain extent.The effect of CNT and Ag particles on the crystalline form of PVDF was similar to that of Fe particles.It should be noted that the former two contributed more significant improvement on the growth of ?-PVDF.The modulus and viscosity of the composites increased with the increasing filler content.As the content of Fe reached 20 vol.%,the modulus and viscosity of Fe/PVDF composites increased significantly when compared to the properties of the samples with 15 vol.%filler.This phenomenon indicated that when CNT content was larger than 5 vol.%,network structure was formed in the matrix due to overlap of CNT particles,and modulus and viscosity of CNT/PVDF composites increased significantly.However,the analysis of Ag/PVDF composites showed that Ag particles at this concentration had limited effect on the non-isothermal crystallization and rheological properties of PVDF matrix.