Polymer Nanocomposite Materials with High Dielectric Permittivity and Low Dielectric Loss Properties

Polymer Nanocomposite Materials with High Dielectric Permittivity and Low Dielectric Loss Properties/nby/nAnju Toor/nDoctor of Philosophy in Mechanical Engineering/nUniversity of California, Berkeley/nProfessor Tarek Zohdi, Co-chair/nProfessor Albert P. Pisano, Co-chair/nMaterials with high dielectric permittivity have drawn increasing interests in recent years/nfor their important applications in capacitors, actuators, and high energy density pulsed power./nParticularly, polymer-based dielectrics are excellent candidates, owing to their properties/nsuch as high breakdown strength, low dielectric loss, flexibility and easy processing. To/nenhance the dielectric permittivity of polymer materials, typically, high dielectric constant/nfiller materials are added to the polymer. Previously, ferroelectric and conductive fillers have/nbeen mainly used. However, such systems suffered from various limitations. For example,/ncomposites based on ferroelectric materials like barium titanate, exhibited high dielectric/nloss, and poor saturation voltages. Conductive fillers are used in the form of powder/naggregates, and they may show 10-100 times enhancement in dielectric constant, however/nthese nanoparticle aggregates cause the dielectric loss to be significant. Also, agglomerates/nlimit the volume fraction of fillers in polymer and hence, the ability to achieve superior/ndielectric constants. Thus, the aggregation of nanoparticles is a significant challenge to their/nuse to improve the dielectric permittivity./nWe propose the use of ligand-coated metal nanoparticle fillers to enhance the dielectric/nproperties of the host polymer while minimizing dielectric loss by preventing nanoparticle/nagglomeration. The focus is on obtaining uniform dispersion of nanoparticles with no/nagglomeration by utilizing appropriate ligands/surface functionalizations on the gold/nnanoparticle surface. Use of ligand coated metal nanoparticles will enhance the dielectric/nconstant while minimizing dielectric loss, even with the particles closely packed in the polymer/nmatrix. Novel combinations of materials, which use 5 nm diameter metal nanoparticles/nembedded inside high breakdown strength polymer materials are evaluated. High breakdown/nstrength polymer materials are chosen to allow further exploration of these materials for/nenergy storage applications./nIn summary, two novel nanocomposite materials are designed and synthesized, one involving/npolyvinylidene fluoride (PVDF) as the host polymer for potential applications in/nenergy storage and the other with SU-8 for microelectronic applications. Scanning elec-/ntron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray/nspectroscopy and ultramicrotoming techniques were used for the material characterization/nof the nanocomposite materials. A homogeneous dispersion of gold nanoparticles with low/nparticle agglomeration has been achieved. Fabricated nanoparticle polymer composite films/nshowed the absence of voids and cracks. Also, no evidence of macro-phase separation of/nnanoparticles from the polymer phase was observed. This is important because nanoparticle/nagglomeration and phase separation from the polymer usually results in poor processability/nof films and a high defect density. Dielectric characterization of the nanocomposite materials/nshowed enhancement in the dielectric constant over the base polymer values and low/ndielectric loss values were observed.

Advisor: Pisano, Albert P.
Zohdi, Tarek