3D Printing: Anisotropic Polymer Nanocomposites with Aligned BaTiO3 Nanowires

Chinese and UK researchers delve into the area of composites for use in the field of energy, releasing their findings in the recently published ‘3D printing of anisotropic polymer nanocomposites with aligned BaTiO₃ nanowires for enhanced energy density.’

In this study, the authors have developed high-performance flexible poly(vinylidene fluoride–chlorotrifluoroethylene) (P(VDF–CTFE)) nanocomposites with aligned BaTiO₃ nanowires using 3D printing. As 3D printing has continued to make enormous impacts in the world of industry—from automotive and racing to aerospace to construction—other areas such as energy storage are being improved too due to the use of new materials, the ability to produce complex technologies, greater affordability, speed, and more.

Main materials used in the research consisted of the following:

• Titanium oxide powders (TiO₂, anatase, 99.9% purity)
• Sodium hydroxide (NaOH, 96% purity)
• Barium hydroxide octahydrate (Ba(OH)₂8H₂O, 99.9% purity)
• Hydrochloric acid solution (HCl, 37 wt%)
• Dimethylformamide solvent (DMF, 99.5% purity)

“The BaTiO₃ nanowires were synthesized by a hydrothermal method according to previous work. Firstly, 1.446 g of TiO₂ was added to 70 ml NaOH solution (10 M) and the mixture was stirred for 2 h to form a homogeneous suspension,” concluded the researchers. “The hydrothermal reactions were carried out at 210 °C under an auto-generated pressure for 24 h in a 100 ml Teflon-lined autoclave. The Na₂Ti₃O₇ products were washed using distilled water and then soaked in diluted 0.2 M HCl solution for 4 h to obtain hydrogen titanate nanowires (H₂Ti₃O₇). Secondly, 0.150 g H₂Ti₃O₇ were dispersed in 70 ml Ba(OH)₂·8H₂O solution (0.1 M) and the mixture was sonicated for 10 min.

“The hydrothermal reactions were carried out at 210 °C under auto-generated pressure for 24 h in a 100 ml Teflon-lined autoclave. The products were soaked in 0.2 M HCl solution briefly, then washed with distilled water several times and dried at 80 °C in an oven.”

Sample nanocomposites were created, with BaTiO₃ nanowires volume fractions of 2.5, 5.0, and 7.5%.

Alignment of BaTiO3 nanowires in nanocomposites: photographs of (a) the printing assembly and (b) a printed nanocomposite sample; schematic illustrations of (c) the alignment of BaTiO3 nanowires in the P(VDF–CTFE) matrix and (d) a nanocomposite capacitor for energy storage applications.

While extruding, BaTiO₃ nanowires aligned parallel due to the high-shear environment.

(a) SEM image of BaTiO3 nanowires; (b) HRTEM image of a single BaTiO3 nanowire; (c) SEM and (d) POM images of nanocomposites prepared by 3D printing with 5 vol% aligned BaTiO3 nanowires.

Varied BaTiO₃ nanowire loadings were fabricated via 3D direct writing for comparison with the other samples made conventionally.

“The permittivity of the nanocomposites with aligned BaTiO₃ nanowires is smaller than that of nanocomposites with random BaTiO₃ nanowires,” stated the researchers. “For example, when the loadings of random BaTiO₃ nanowires is 2.5, 5.0 and 7.5 vol%, the permittivity of the nanocomposites with random BaTiO₃ nanowires is 14, 15.5 and 21.5, respectively, while the permittivity of the nanocomposites with aligned BaTiO₃ nanowires is 12, 14 and 17.5, respectively.”

Frequency dependence of (a) relative dielectric permittivity and (b) dielectric loss of BaTiO3/P(VDF–CTFE) nanocomposites with aligned BaTiO3 nanowires, (c) relative dielectric permittivity of nanocomposites with random distributed BaTiO3 nanowires; (d) relative dielectric permittivity of the nanocomposites as a function of volume fraction at 1 kHz.

It was noted that saturation polarization accelerated with increasing BaTiO₃ loading because of high permittivity of fillers and interfacial polarization.

“The discharged energy density of all composites is similar at low field, but at high field increases with increasing loading level. The maximum energy density achieved in nanocomposites with aligned BaTiO₃ nanowires was 14.52 J cm⁻³ for the sample with 5.0 vol% loading, which is 55% higher than that of the nanocomposite with randomly aligned BaTiO₃ nanowires at the same loading level,” concluded the researchers. “The results showed that the composite with 5.0 vol% BaTiO₃ nanowires get the balance point, which simultaneously achieved high polarization and breakdown strength.”

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