UC Berkeley

Polymers are primarily known as insulators with low electrical conductance which make them potentially good candidates as electret materials to store high surface charges for various applications. This work focuses on the investigations of electrostatic charging process and the capability of electret polymers for two specific applications in energy harvesting and air filtration systems.An energy harvester can use polymeric electret materials in the form of a parallel-plat capacitor to convert mechanical deformations to electrical energy outputs. A prototype piezoelectret device made of FEP (fluorinated ethylene propylene) as the top and bottom electret layers, PET (polyethylene terephthalate) as the middle layer, and EVA (ethylene-vinyl acetate) as the adhesion layer at the boundary has been proposed and demonstrated. A device of 3 cm x 2 cm in size shows a peak output voltage of 8 Volts and 2 μA under the manual compression condition. By using the standard 40 kHz ultrasonic excitation in a beaker under the water environment, a voltage output of 7 Volts has been generated, which is used in the electrolysis process to generate hydrogen at a measured rate of 0.217 ppm/min. A second piezoelectret energy harvester is proposed and constructed based on biodegradable materials. The device consists of cellulose as the structural supporting layer, PLA (polylactic acid) as the electret, and PEDOT: PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) as the conductive electrode. Experimental results show the device can generate an output peak-to-peal voltage of 12 Volts under pressure applied by a human hand and hold an initial surface charge of 148 Volts. Preliminary studies have also been performed on silicon dioxide, which has the highest reported surface charge density at the level of 3400 nC/cm2, about 1~2 orders of magnitude higher than those of polymer materials. However, the high residual stress issue causes the sever defects of the SiO2 films. In the third study, polymeric electret materials are investigated for applications in air filtration systems. Several commercial filters are tested for their surface charge potential and longevity. Results show surface potentials in the ambient environment as high as 125 Volts can be maintained over a month-long period. By conducting a new Corona charging process, surface potential as high as 1000V can be achieved for the potential attraction and stiction of harmful viruses and the UV light is proposed as the follow-up process to destruct viruses for applications such as to prevent the spread of COVID-19.