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

Polymer Nanocomposite Materials with High Dielectric Permittivity and Low Dielectric Loss PropertiesbyAnju ToorDoctor of Philosophy in Mechanical EngineeringUniversity of California, BerkeleyProfessor Tarek Zohdi, Co-chairProfessor Albert P. Pisano, Co-chairMaterials with high dielectric permittivity have drawn increasing interests in recent yearsfor their important applications in capacitors, actuators, and high energy density pulsed power.Particularly, polymer-based dielectrics are excellent candidates, owing to their propertiessuch as high breakdown strength, low dielectric loss, flexibility and easy processing. Toenhance the dielectric permittivity of polymer materials, typically, high dielectric constantfiller materials are added to the polymer. Previously, ferroelectric and conductive fillers havebeen mainly used. However, such systems suffered from various limitations. For example,composites based on ferroelectric materials like barium titanate, exhibited high dielectricloss, and poor saturation voltages. Conductive fillers are used in the form of powder aggregates, and they may show 10-100 times enhancement in dielectric constant, howeverthese nanoparticle aggregates cause the dielectric loss to be significant. Also, agglomerates limit the volume fraction of fillers in polymer and hence, the ability to achieve superior dielectric constants. Thus, the aggregation of nanoparticles is a significant challenge to their use to improve the dielectric permittivity.We propose the use of ligand-coated metal nanoparticle fillers to enhance the dielectric properties of the host polymer while minimizing dielectric loss by preventing nanoparticle agglomeration. The focus is on obtaining uniform dispersion of nanoparticles with no agglomeration by utilizing appropriate ligands/surface functionalizations on the gold nanoparticle surface. Use of ligand coated metal nanoparticles will enhance the dielectric constant while minimizing dielectric loss, even with the particles closely packed in the polymer matrix. Novel combinations of materials, which use 5 nm diameter metal nanoparticles embedded inside high breakdown strength polymer materials are evaluated. High breakdown strength polymer materials are chosen to allow further exploration of these materials for energy storage applications.In summary, two novel nanocomposite materials are designed and synthesized, one involvingpolyvinylidene fluoride (PVDF) as the host polymer for potential applications inenergy storage and the other with SU-8 for microelectronic applications. Scanning elec-tron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-rayspectroscopy and ultramicrotoming techniques were used for the material characterizationof the nanocomposite materials. A homogeneous dispersion of gold nanoparticles with lowparticle agglomeration has been achieved. Fabricated nanoparticle polymer composite filmsshowed the absence of voids and cracks. Also, no evidence of macro-phase separation ofnanoparticles from the polymer phase was observed. This is important because nanoparticleagglomeration and phase separation from the polymer usually results in poor processabilityof films and a high defect density. Dielectric characterization of the nanocomposite materialsshowed enhancement in the dielectric constant over the base polymer values and low dielectric loss values were observed