1 research outputs found
Conductive Network and β Polymorph Content Evolution Caused by Thermal Treatment in Carbon Nanotubes-BaTiO<sub>3</sub> Hybrids Reinforced Polyvinylidene Fluoride Composites
A good
dispersion of carbon nanotube (CNT) in polyvinylidene fluoride
(PVDF) is realized by using CNT and BaTiO<sub>3</sub> (BT) hybrids
(H-CNT-BT) with a special core–shell structure. Thus, a high
dielectric performance is achieved for the composite (H-CNT-BT/PVDF).
Carried by BT, CNT is easy to connect with each other and thus more
interface area may be created which helps to achieve an extremely
low percolation threshold (<i>f</i><sub>c</sub>). Moreover,
the dielectric permittivity of the composite near <i>f</i><sub>c</sub> is increased more than three times after thermal treatment
while dielectric loss remains at a low level. In order to study more
comprehensively about the influence of thermal treatment, in situ
synchrotron X-ray is used to detect recrystalline behavior of PVDF.
Results of wide-angle X-ray diffraction (WAXD) and small-angle X-ray
scattering (SAXS) show that after thermal treatment, the content of
β polymorph has increased nearly double times at the interface
of CNT-PVDF, and the thickness of amorphous layers (<i>L</i><sub>a</sub>) in PVDF’s long periods (<i>L</i><sub>p</sub>) has shrunk around 10 Å. Increased β polymorph
at the interface of CNT-PVDF may form an ideal structure with the
grading dielectric permittivities from the center to the border which
decreases the contrast between CNT and PVDF. Meanwhile, the evolution
of CNT’s network possibly occurs in the procedure of <i>L</i><sub>a</sub> shrinkage, where the strong interfacial polarization
may be aroused. Besides, an increase in the thickness of crystalline
lamella may also arouse more orientational polarization and improve
dielectric properties at high frequency. Combining with BT’s
buffer role for blocking possible leakage current during the percolative
behavior, the dielectric loss of composite can remain at a very low
level even after thermal treatment. In addition, experimental results
show that prolonging annealing duration or increasing annealing cycles
favors stabilization of CNT’s dynamic percolation, which reduces
the sensitivity of CNT’s network in the composite and further
improves dielectric properties. After thermal
treatment, the dielectric permittivity reachs 1172, but dielectric
loss remains at 0.55 at 100 Hz. To our best knowledge, this high dielectric
performance is really rare, only found in recent reports