Enhancing dielectric breakdown strength: structural relaxation of amorphous polymers and nanocomposites
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Polymers/Soft Matter Research Letter
Enhancing dielectric breakdown strength: structural relaxation of amorphous polymers and nanocomposites Christopher A. Grabowski, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio 45433; UES, Inc., Dayton, Ohio 45432, USA Hilmar Koerner and Richard A. Vaia, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio 45433, USA Address all correspondence to Richard A. Vaia at [email protected] (Received 3 March 2015; accepted 28 April 2015)
Abstract The thermal history of amorphous polymers near the glass-transition temperature determines the extent to which macromolecules structurally relax, and ultimately their properties. Here, we report the correlation between physical aging, dielectric breakdown, and capacitive energy storage of polystyrene, poly(methyl-methacrylate), and associated silica nanocomposites. Guided by enthalphic recovery rates, dielectric breakdown strength increased from 20% to 40% when aged at Tg−10 °C before use. The generality of improvement and connection to enthalpic recovery afford a means to design pre-service processing of new polymers and additive manufacturing techniques to reduce excess volume within the glass; and thereby reduce initiation and inhibit propagation of electronic failure.
Simultaneously improving the power and energy density of electrostatic capacitors, and decreasing the size of the power subsystem, is critical for advancing medical, transportation, and aerospace technologies.[1] Furthermore, the rapid emergence of flexible hybrid electronics and printing technologies promises to integrate passives into the device package and eliminate surface-mounted components. To maximize theoretical energy storage density (=1/2εoεr|EBD|2), the relative permittivity εr and breakdown strength EBD must be concurrently increased by approaches that optimize new materials with new processing techniques. Although amorphous polymers have relatively low εr, their high breakdown strength, ease of processability, and affordability offer practical advantages over pure ceramics, and thus are the current choice for many emerging applications and manufacturing technologies. The addition of inorganic nanoparticles with substantially higher εr conceptually affords a means to increase permittivity while maintaining the polymeric characteristics that are key to scalability.[2] In concert with these material innovations, processing is just as critical to maximize energy storage. In addition to purification, protocols must avoid trapped solvent and voids. Such defects serve as initiation sites for premature breakdown, and lower the effective dielectric strength.[3] The relation between this “free-volume” and dielectric breakdown strength has been established; for example by experiments on amorphous copolymers[4] and through percolation theory simulations.[5] Initiation of breakdown within a polymer is associated with the largest voids,[6] and has been use
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