Low magnetic field-induced alignment of nickel particles in segregated poly (L-lactide)/poly(epsilon-caprolactone)/multi-walled carbon nanotube nanocomposites: Towards remarkable and tunable conductive anisotropy

Anisotropic conductive composites with segregated conductive networks were constructed in poly(L-lactide)/poly(epsilon-caprolactone)/multi-walled carbon nanotubes/nickel (PLLA/PCL/MWCNT/Ni) composites by aligning Ni particles using a low magnetic field. Firstly, MWCNTs were melt-mixed with PLLA to form PLLA/MWCNT composites and then pulverized into microscale PLLA/MWCNT particles 425-850 mu m in size. Later, the Ni particles were dispersed in PCL to yield PCL/Ni composites and then mixed with PLLA/MWCNT particles at 100 degrees C, a temperature lying in between the melting temperatures of PCL and PLLA. The coated PLLA/MWCNT particles were compressed to form PLLA/PCL/MWCNTs/Ni composites with segregated structures. A remarkable conductive anisotropy was observed in the segregated samples after magnetic alignment in a low magnetic field of similar to 47.5 mT at 100 degrees C for 30 min. The electrical conductivity of the segregated samples diametrically increased in the direction parallel to the magnetic field, but decreased in the direction perpendicular to the magnetic field after the magnetic alignment of Ni particles in the PCL phase. Electrical conductivity in the parallel direction was almost eight orders of magnitude higher than that in the perpendicular direction at 3.0 wt% Ni and 0.7 wt% MWCNTs. Conductive anisotropy in the segregated systems could also be easily regulated by controlling the treatment time or changing the direction of the magnetic field. However, electrical conductivity could be maintained in both vertical and parallel directions in conventional composites after magnetic treatment because Ni particles preferably dispersed in the continuous PLLA phase, in which the Ni particles cannot be aligned at 100 degrees C. In addition, these segregated samples with alignment of Ni particles also exhibited the mechanical enhancement and high-performance electromagnetic interference shielding.