Dielectric Material Research
Since capacitors can store energy for a long period of time, seconds, and deliver it to a load in a fraction of this time, they have found roles in energy storage, electronics and electromechanical devices. Capacitance in a parallel plate capacitor is governed by the following equation;
C = εoεrA/d
where εo is the vacuum permittivity constant, εr is the dielectric constant of the insulating medium, A is the area and d is the distance between the electrodes. High capacitance is needed in order to increase the stored electrostatic energy for pulsed power applications or in the case of field effect transistors (FET), Figure 1(a) and (b), the transconductance. However, the operating limits of the common dielectric materials used in these applications, biaxially oriented polypropylene (BOPP) for energy storage and SiO2 for FETs, are being met as devices become smaller and space becomes limited since decreasing the distance between the electrodes leads to leakage affects.
Figure 1. Dielectric properties of (a) polyimide (BTDA/HK511) based on 3,3’,4,4’-benzophenone-tetracarboxylic dianhydride (BTDA) and Jeffamine HK511 and (b) poly(dimethyltin glutarate). The illustration at top right represents one octahedral complex that organotin polymers take.
Since the chemical space of new dielectric materials is so vast, our synthetic efforts are very collaborative with theoreticists to narrow the search area to a handful of promising, synthesizable candidates. As a result our research focus is split between traditional organic and more “exotic” organometallic polymers, Figure 1. Even though the research is split into two different types of materials there is much commonality between them. In both areas we focus on the synthesis of high functional group density polymers to increase the total polarization of the polymer backbone and drive the dielectric constant higher. Our syntheses must also result in low impurity formation, since in the case of salt impurities cause detrimental effects in terms of conductivity of the polymer films. To determine the feasibility of these materials the electronic part of the dielectric constant (εelec), the total dielectric constant (εtot), dielectric loss and band gap are measured. Once a material is deemed to be a promising candidate, high dielectric constant and band gap with low dielectric loss, for further study, a preliminary determination of the maximum field, E, is performed since energy density, u, is related through the following;
u = ½εoεrE2
At the same time the synthesis is scaled up to deliver anywhere from multi-gram to kilogram batches to processing engineers to further optimize the polymer films.
In summary our research spans the small scale fundamental understanding of how polymer structure affects the dielectric properties to reproducible large scale synthesis of promising materials. Our research is highly collaborative with both theoreticists and electrical and processing engineers and allows for us to learn the whole spectrum from discovery to development.
Papers
R. G. Lorenzini, G. A. Sotzing, J. Appl. Polym. Sci. 2013, doi: 10.1002/app.40179.
R. G. Lorenzini, W. M. Kline, C. C. Wang, R. Ramprasad, G. A. Sotzing, Polymer 2013, 54, 3529-3533.
A. F. Baldwin, R. Ma, C. C. Wang, R. Ramprasad, G. A. Sotzing, J. Appl. Polym. Sci. 2013, 130, 1276-1280.
Conferences
A. F. Baldwin, Rui Ma, A. Mannodi-Kanakkithodi, T. D. Huan, C. C. Wang, J. Marszalek, M. Cakmak, R. Ramprasad, G. A. Sotzing Rationally Designed Poly(dimethyltin esters) as High Dielectric Organometallic Polymers for Energy Storage Applications presented at 247th ACS National Meeting, Dallas, TX, USA, March, 2014.
R. Ma, A. F. Baldwin, C. C. Wang, R. Ramprasad, G. A. Sotzing Rationally Designed Polyimide Thin Films for High Energy Density Capacitor Applications presented at 247th ACS National Meeting, Dallas, TX, USA, March, 2014.
R. G. Lorenzini, G. A. Sotzing, C. C. Wang, R. Ramprasad Heteroatom-containing Polymers as Dielectric Materials presented at 247th ACS National Meeting, Dallas, TX, USA, March, 2014.
A. F. Baldwin, Rui Ma, C. C. Wang, R. Ramprasad, G. A. Sotzing High Functionality Polyimides Based on Pyromellitic Dianhydride for High Energy Density Capacitors presented at Third International Symposium Frontiers in Polymer Science, Sitges, Spain, May, 2013.