Effects of conductive polymer composite layering on EMI shielding during additive manufacturing
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.326
Effects of conductive polymer composite layering on EMI shielding during additive manufacturing 1
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Eugene Zakar , Theodore Anthony , Madan Dubey 1
U.S. Army Research Laboratory
Abstract: Spin coating and drop casting are viable methods for rapid and low-cost additive manufacturing of components for flexible devices and sensors. We investigated the cumulative effects of layering a conductive polymer composite 2 wt% MWCNT filler in PEDOT:PSS on a Mylar substrate for application to electromagnetic interference (EMI) shielding. The optical transmittace of spin coated composite layers is 90%, 45%, and 20% with a thickness of 0.05 μm, 0.15 μm, and 0.45 μm respectively. Drop cast composite layers have 0% transmittance due to their much greater starting thickness of 4.4 μm. The addition of isopropyl alcohol (IPA) to the solution mixture and substrate heating to 40 °C improves the conductivity, and drying time of the cured composite layers to 10 min. This study shows that the cumulative effects of composite layering are additive, but the electrical properties do not scale the same way. A significant increase in the EMI SE is mainly attributed to the enhanced electrical conductivity of the composite. The insertion of a 50 μm gap in between two 15 μm composite layers accentuates the EMI shielding effectiveness (SE) significantly to a peak of 21 dB within a narrow frequency range in the Ku-band tested.
INTRODUCTION: Electromagnetic interference (EMI) has emerged as a major concern in the development of electronic, optoelectronic, and wearable devices because of the increasing use of high frequencies and broad bandwidths. Although all electronics emit magnetic and electrical energy, if this energy unintentionally interacts with another device and causes it to malfunction, then it is considered interference. The recent development nano-carbon decorated composites provides a revolutionary approach to the mitigation of high EMI radiation owing to its superior conductivity, flexibility and corrosion resistance characteristics in harsh environments compared to traditional metallic Faraday cages and structures [1]. PEDOT:PSS, poly (3,4-ethylenedioxythiophene): poly (styrenesulfonic acid) is a water based conductive polymer that easily mixes and enhances the dispersion
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of nano-carbon based materials [2-6]. The combination of conductive polymers with MWCNT have become attractive materials for EMI shielding applications recently [7]. Removal of solvents in the polymers by evaporation, and in improving the structural integrity of printed layers without delamination or distortion upon drying [8] is a great concern. IPA is a common solvernt that has a low boiling point (92.5 °C) than other dopants like glycerol (29
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