Synthesis and characterization of poly(vinylidene fluoride)/carbon nanotube composite piezoelectric powders
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Nanocomposite piezoelectric powders comprising polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) were synthesized using a novel process, which combines ultrasonication and solventnonsolvent mixture-induced crystallization at very low temperatures #10 °C. The morphological and thermal properties of these composite powders were extensively studied. Scanning electron microscopy characterization showed that these composite powders have polymer particles with an average diameter of 150 nm. Fourier transform infrared spectroscopy, differential scanning calorimetry and wide-angle x-ray scattering analyses confirmed that at CNT concentrations of 0.05–20 wt% this process introduces the b-phase in both PVDF/single-walled CNT (SWCNT) and PVDF/multiwalled CNT (MWCNT) composite powders. Both types of composite powders (PVDF-multiwalled and PVDF-single-walled nanotubes) have shown piezoelectric response at different voltages up to 1% loading of multiwalled nanotubes (MWCNTs) and 0.5% loading of single-walled nanotubes (SWCNTs) in composites.
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.230
as a powder that can be formed by powder processing7 and spray drying.8 The drawback of these powder preparations is that they neither produce very uniformly sized polymer particles nor very well distributed CNTs in the polymer matrix. For overcoming these limitations, in this work, a very low-temperature-induced solvent-nonsolvent phase separation technique has been used to synthesize composite powders comprising CNTs and polyvinylidene fluoride (PVDF). In this study, PVDF has been selected as the polymer matrix because of its piezoelectric properties and one goal of this study is to investigate whether this property can be retained or enhanced in powder composite of PVDF with CNT. Piezoelectric property of PVDF is associated with its b crystalline form9,10 and among many ways to enhance the formation of b phase, such as crystallization from solution,11,12 crystallization from melt blending,13 through orientation by applying forces14 at 80–100 °C, several research groups reported the enhancement of b phase formation in PVDF composite films15–17 by the addition of multiwalled nanotubes (MWCNTs) into the PVDF matrix. Present research has demonstrated that both single-walled carbon nanotubes (SWCNTs) and MWCNTs have enhanced the b phase within PVDF powders. Although soft and hard piezoceramic powders are commonly reported18 to be used as sensors and in other applications, polymers are rarely reported to have been used as piezoelectric materials in powder form. The problem associated with the brittleness of ceramic composites can be overcome by the polymer-based composite. The process of ultrasonication coupled with low-temperature-induced phase separation and the presence of CNTs not only introduced the b phase in the powder form, but also enhanced the amount of b phase in
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Ó Materials Research Society 2012
I. INTRODUCTION
Carbon nanotubes (CNT)/polymer composites are an important class
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