Fabrication of barium titanate nanoparticles-polymethylmethacrylate composite films and their dielectric properties

Fabrication of barium titanate nanoparticles-polymethylmethacrylate composite films and their dielectric properties

Composite films composed of polymer films and dielectric ceramics such as titanates are of high interest in material science fields. The incorporation of titanates is expected to allow the host polymer to have high capacitance and to make it easy to process the films owing to the increased flexibility of the composite.

Various methods for fabricating titanate-polymer composite films have been reported. In most reports, the composite films are fabricated by mixing a dielectric polymer solution and submicron- or micron-sized ferroelectric particles, and evaporating the solvent of the polymer solution (1-6).

However, the use of these particles cannot be applied to production of composite films with high transparency.

In the fabrication of electric devices with high capacitance, practical composite films need to have a thin film thickness of less than one micron. Surface smoothness of the films is another requirement for the fabrication of practical dielectric devices, because films with smooth surface show stable dielectric properties. The use of nanometer-sized titanate particles can help to address these requirements and moreover could allow formation of films with high transparency.

Homogeneous dispersion of particles dispersed into the film could be expected to make the films transparent.

For the homogeneous dispersion, the titanate nanoparticles are required to be colloidally stable in precursor solution, and affinity between the titanate nanoparticles and host polymer has to be strengthened. Many previous researchers have applied surface modification to the dispersion. Ramesh et al. fabricated barium titanate

(BT)-epoxy nanocomposites with the use of BT nanoparticles surface-modified with various silanes

(2).
Among the silanes examined, the silanes with epoxy, thiol, and phenyl amino functionalities resulted in production of homogeneous composite materials and high dielectric constants.

Kim et al. performed surface-modification of BT nanoparticles by phosphonic acids with functional groups, and fabrication of BT-polymer (polycarbonate or poly (vinylidenefluoride-co-hexafluoropropylene)) composite films (7).

The composite films fabricated with the use of surface-modified BT nanoparticles yielded uniform films with homogeneous nanoparticle dispersions. In the work of Li et al.

(8), BT-polyamide (PA)-bismaleimide (BMI) composites were fabricated with the use of phthalocyanine-coated BT nanoparticles.

Addition of Ni nano-particles to the composites and the combination of PA with BMI were confirmed to increase their dielectric constants and to improve the processability of matrix, respectively. Yogo and coworkers

(9) fabricated transparent and self-standing BT-poly(methylmethacrylate)
(PMMA) composite films with polymerization of methylmethacrylatc
(MMA) in the presence of the BT particles with the C=C bonds that were prepared with hydrolysis of complex alkoxide with 2-vinyloxyethanol. They also synthesized BT-polymer nanocomposite films with the use of alkoxide modified with methacryloxyethoxy group(10).

In previous work, we developed techniques for fabricating polymer films containing barium titanate nanoparticles (11-13).

BT nanoparticles prepared in the presence of poly(vinylpyrrolidone) (PVP) are suitable for fabricating BT-polymer films with smooth surface when compared with cases in the absence of PVP (13).

Particle surface-modification is effective for colloidal stability, and consequently for producing composite films of high-quality.

The present work proposes a method for fabrication of BT-PMMA composite films by the application of surface-modification of BT nanoparticles. The BT nanoparticles with a perovskite crystalline structure were prepared from complex alkoxide with a sol-gel method.

To increase affinity between BT particle surface and PMMA host polymer and to stabilize the BT particles colloidally, the BT particles were coated with PMMA by polymerizing MMA monomer on the BT particle surface. Before the polymerization, C=C bonds were introduced onto the BT particle surface with silane coupling agents with the C=C bonds, so that the surface was expected to react with the MMA monomer.

The BT-PMMA composite films were fabricated by spin-coating precursor solution containing PMMA and the PMMA-coated BT particles on glass substrates. Measurements were performed to study the effects of PMMA-coating and BT particle size on surface roughness and dielectric properties of the films

Barium titanate films for improved capacitors.(ELECTRONICS)
Advanced Ceramics Report, June, 2007

Scientists at Georgia Institute of Technology (Georgia Tech), USA, have developed a technique for creating films of barium titanate nanoparticles in a polymer matrix, which could allow fabrication of capacitors able to store twice as much energy as existing devices. The improved capacitors could be used in consumer devices such as cellular telephones, as well as in defence applications requiring both high energy storage and rapid current discharge.

Due to its high dielectric properties, barium titanate has long been of interest for use in capacitors, but until recently materials scientists had been unable to produce good dispersion of the material within a polymer matrix. By using tailored organic phosphonic acids to encapsulate and modify the surface of the...