TY - JOUR A1 - Assagra, Yuri A.O. A1 - Altafim, Ruy Alberto Pisani A1 - do Carmo, Joao P. A1 - Altafim, Ruy A.C. A1 - Rychkov, Dmitry A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - A new route to piezo-polymer transducers: 3D printing of polypropylene ferroelectrets JF - IEEE transactions on dielectrics and electrical insulation N2 - Here, a promising approach for producing piezo-polymer transducers in a one-step process is presented. Using 3D-printing technology and polypropylene (PP) filaments, we are able to print a two-layered film structure with regular cavities of precisely controlled size and shape. It is found that the 3D-printed samples exhibit piezoelectric coefficients up to 200 pC/N, similar to those of other PP ferroelectrets, and their temporal and thermal behavior is in good agreement with those known of PP ferroelectrets. The piezoelectric response strongly decreases for applied pressures above 20 kPa, as the pressure in the air-filled cavities strongly influences the overall elastic modulus of ferroelectrets. KW - 3D printing KW - polymer ferroelectrets KW - sensors and actuators KW - piezoelectrets KW - electret polymers KW - soft electro-active materials KW - functional materials KW - soft matter Y1 - 2020 U6 - https://doi.org/10.1109/TDEI.2020.008461 SN - 1070-9878 SN - 1558-4135 VL - 27 IS - 5 SP - 1668 EP - 1674 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Wang, Jingwen A1 - Rychkov, Dmitry A1 - Nguyen, Quyet Doan A1 - Gerhard, Reimund T1 - Unexpected bipolar space-charge polarization across transcrystalline interfaces in polypropylene electret films JF - Journal of applied physics N2 - A double-layer transcrystalline polypropylene (PP) film with a flat central interface layer between its two transcrystalline layers is obtained by recrystallization from the melt between two polytetrafluoroethylene (PTFE) surfaces on both sides of the PP film. Its electret properties are studied and compared with those of a single-layer transcrystalline PP film re-crystallized in contact with only one PTFE surface. Within experimental uncertainty, the two types of transcrystalline films exhibit the same thermal properties and crystallinities. After thermal poling, however, two hetero-charge layers of opposite polarity are found on the internal interfaces of the double-layer transcrystalline films and may together be considered as micrometer-sized dipoles. The unexpected phenomenon does not occur in single-layer transcrystalline samples without a central interface layer, suggesting that the interfaces between the transcrystalline layers and the micrometer-thick central interface layer may be the origin of deeper traps rather than the crystalline structures in the transcrystallites or the spherulites. The origin of the interfacial charges was also studied by means of an injection-blocking charging method, which revealed that intrinsic charge carriers introduced during recrystallization are most likely responsible for the interfacial charges. It is fascinating that a material as familiar as PP can exhibit such intriguing properties with a special bipolar space-charge polarization across the central interface layer after quasi-epitaxial surface moulding into a double-layer transcrystalline form. In addition to applications in electret (micro-)devices for electro-mechanical transduction, the highly ordered structures may also be employed as a new paradigm for studying charge storage and transport in polymer electrets and in dielectrics for DC electrical insulation. Y1 - 2020 U6 - https://doi.org/10.1063/5.0022071 SN - 0021-8979 SN - 1089-7550 VL - 128 IS - 13 PB - American Institute of Physics, AIP CY - Melville, NY ER - TY - JOUR A1 - Wang, Jingwen A1 - Rychkov, Dmitry A1 - Gerhard, Reimund T1 - Space-charge electret properties of polypropylene films with transcrystalline or spherulitic structures BT - a comparison of functionalities at interfaces JF - Journal of applied physics : AIP's archival journal for significant new results in applied physics / publ. by the American Institute of Physics N2 - Spherulite-related space-charge electret properties of polypropylene (PP) have been widely discussed in the past decades. In the present paper, a less-common crystalline structure in PP-transcrystalline PP-is studied regarding its electret behavior in comparison with the typical spherulitic morphology. Polarized light microscopy and differential scanning calorimetry were employed to characterize the crystallite types and crystallinities of transcrystalline and spherulitic PP. Their electret functionality is investigated by means of thermally stimulated discharge experiments, where the cross-over phenomenon is observed on transcrystalline PP films, whereas surface-potential saturation and undercharging on the surface occur on the spherulitic samples. Besides, an asymmetrical behavior of positive and negative surface-charge stabilities is found on PP with spherulites, the negatively charged spherulitic surfaces show a better charge stability. It is shown that PP electrets are very sensitive to changes in the microscopic crystalline structures and their interfaces as well as in the molecular conformations controlled through adjustments of the respective processing steps. In addition, surface and bulk nanocomposites of PP or low-density polyethylene with inorganic particles are included in the comparison. In view of recent developments in the areas of PP-based electret-fiber filters and cellular-foam ferroelectrets, the observed changes in the charge-storage properties may have particular relevance, as the required film, fiber, or foam processing might significantly modify crystalline morphologies and nano-scale interfaces in PP electrets. Limitations in the charge-storage capabilities of interface structures may also be of interest in the context of high-voltage electrical-insulation materials where reduced space-charge accumulation and slightly increased charge transport can be advantageous. Y1 - 2021 U6 - https://doi.org/10.1063/5.0039867 SN - 0021-8979 SN - 1089-7550 VL - 129 IS - 6 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Wang, Jingwen A1 - Rychkov, Dmitry A1 - Nguyen, Quyet Doan A1 - Gerhard, Reimund T1 - The influence of orthophosphoric-acid surface modification on charge-storage enhancement in polypropylene electrets JF - Journal of applied physics N2 - Bipolar electrets from polypropylene (PP) are essential, e.g., in electret air filters and in cellular-foam ferroelectrets. Therefore, the mechanism of surface-charge stability enhancement on PP electrets via orthophosphoric-acid surface treatment is investigated in detail. It is shown that the significant charge-stability enhancement can be mainly attributed to deeper surface traps originating from deposited chemicals and topographic features on the modified surfaces. Thermally stimulated discharge of chemically treated and non-treated PP films with different surface-charge densities is used to test the limits of the newly formed deep traps in terms of the capacity for hosting surface charges. When the initial surface-charge density is very high, more charges are forced into shallower original traps on the surface or in the bulk of the treated PP samples, reducing the effect of the deeper surface traps brought by the surface modification. The well-known crossover phenomenon (of the surface-charge decay curves) has been observed between modified PP electrets charged to +/- 2kV and to +/- 3kV. Acoustically probed charge distributions in the thickness direction of PP electrets at different stages of thermal discharging indicate that the deep surface trapping sites may have preference for negative charges, resulting in the observed asymmetric charge stability of the modified PP films. Y1 - 2020 U6 - https://doi.org/10.1063/5.0013805 SN - 0021-8979 SN - 1089-7550 VL - 128 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - GEN A1 - Loupos, Konstantinos A1 - Damigos, Yannis A1 - Amditis, Angelos A1 - Gerhard, Reimund A1 - Rychkov, Dmitry A1 - Wirges, Werner A1 - Schulze, Manuel A1 - Lenas, Sotiris-Angelos A1 - Chatziandreoglou, Christos A1 - Malliou, Christina A1 - Tsaoussidis, Vassilis A1 - Brady, Ken A1 - Frankenstein, Bernd T1 - Structural health monitoring system for bridges based on skin-like sensor T2 - IOP conference series : Materials science and engineering N2 - Structural health monitoring activities are of primal importance for managing transport infrastructure, however most SHM methodologies are based on point-based sensors that have limitations in terms of their spatial positioning requirements, cost of development and measurement range. This paper describes the progress on the SENSKIN EC project whose objective is to develop a dielectric-elastomer and micro-electronics-based sensor, formed from a large highly extensible capacitance sensing membrane supported by advanced microelectronic circuitry, for monitoring transport infrastructure bridges. Such a sensor could provide spatial measurements of strain in excess of 10%. The actual sensor along with the data acquisition module, the communication module and power electronics are all integrated into a compact unit, the SENSKIN device, which is energy-efficient, requires simple signal processing and it is easy to install over various surface types. In terms of communication, SENSKIN devices interact with each other to form the SENSKIN system; a fully distributed and autonomous wireless sensor network that is able to self-monitor. SENSKIN system utilizes Delay-/Disruption-Tolerant Networking technologies to ensure that the strain measurements will be received by the base station even under extreme conditions where normal communications are disrupted. This paper describes the architecture of the SENSKIN system and the development and testing of the first SENSKIN prototype sensor, the data acquisition system, and the communication system. Y1 - 2017 U6 - https://doi.org/10.1088/1757-899X/236/1/012100 SN - 1757-8981 VL - 236 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Wang, Jingwen A1 - Rychkov, Dmitry A1 - Gerhard, Reimund T1 - Influence of Charge Density on Charge Decay in Chemically Modified Polypropylene Films T2 - 2018 IEEE 2nd International Conference on Dielectrics (ICD) N2 - Previous work has shown that surface modification with orthophosphoric acid can significantly enhance the charge stability on polypropylene (PP) surface by generating deeper traps. In the present study, thermally stimulated potential-decay measurements revealed that the chemical treatment may also significantly increase the number of available trapping sites on the surface. Thus, as a consequence, the so-called "cross-over" phenomenon, which is observed on as-received and thermally treated PP electrets, may be overcome in a certain range of initial charge densities. Furthermore, the discharge behavior of chemically modified samples indicates that charges can be injected from the treated surface into the bulk, and/or charges of opposite polarity can be pulled from the rear electrode into the bulk at elevated temperatures and at the high electric fields that are caused by the deposited charges. In the bulk, a lack of deep traps causes rapid charge decay already in the temperature range around 95 degrees C. KW - polypropylene KW - surface charge stability KW - thermally stimulated discharge KW - cross-over effect KW - chemical modification Y1 - 2018 SN - 978-1-5386-6389-9 U6 - https://doi.org/10.1109/ICD.2018.8514718 PB - IEEE CY - New York ER - TY - GEN A1 - Rychkov, Andrey A1 - Stojharov, Valery A1 - Kuznetsov, Alexey A1 - Rychkov, Dmitry T1 - The influence of recrystallization regimes on electret charge stability in low-density polyethylene films T2 - 2018 IEEE 2nd International Conference on Dielectrics (ICD) N2 - The electret state stability in nonpolar semicrystalline polymers is largely determined by the traps located at crystalline/ amorphous phase interfaces. Thus, the thermal history of such polymers should considerably influence their electret properties. In the present work, we investigate how recrystallization influences charge stability in low-density polyethylene corona electrets. It has been found that electret charge stability in quenched samples is higher than in slowly-crystallized ones. Phenomenologicaly, this can be explained by the increased number of deeper traps in samples with smaller crystallite size. KW - electrets KW - low-density polyethylene KW - crystallinity KW - quenching KW - recrystallization Y1 - 2018 SN - 978-1-5386-6389-9 SN - 978-1-5386-6388-2 SN - 978-1-5386-6390-5 U6 - https://doi.org/10.1109/ICD.2018.8514638 PB - IEEE CY - New York ER - TY - GEN A1 - Cheilakou, E. A1 - Tsopelas, N. A1 - Anastasopoulos, A. A1 - Kourousis, D. A1 - Rychkov, Dmitry A1 - Gerhard, Reimund A1 - Frankenstein, B. A1 - Amditis, A. A1 - Damigos, Y. A1 - Bouklas, C. T1 - Strain monitoring system for steel and concrete structures T2 - Procedia Structural Integrity N2 - The present work is part of a collaborative H2020 European funded research project called SENSKIN, that aims to improve Structural Health Monitoring (SHM) for transport infrastructure through the development of an innovative monitoring and management system for bridges based on a novel, inexpensive, skin-like sensor. The integrated SENSKIN technology will be implemented in the case of steel and concrete bridges, and tested, field-evaluated and benchmarked on actual bridge environment against a conventional health monitoring solution developed by Mistras Group Hellas. The main objective of the present work is to implement the autonomous, fully functional strain monitoring system based on commercially available off-the-shelf components, that will be used to accomplish direct comparison between the performance of the innovative SENSKIN sensors and the conventional strain sensors commonly used for structural monitoring of bridges. For this purpose, the mini Structural Monitoring System (mini SMS) of Physical Acoustics Corporation, a comprehensive data acquisition unit designed specifically for long-term unattended operation in outdoor environments, was selected. For the completion of the conventional system, appropriate foil-type strain sensors were selected, driven by special conditioners manufactured by Mistras Group. A comprehensive description of the strain monitoring system and its peripheral components is provided in this paper. For the evaluation of the integrated system’s performance and the effect of various parameters on the long-term behavior of sensors, several test steel pieces instrumented with different strain sensors configurations were prepared and tested in both laboratory and field ambient conditions. Furthermore, loading tests were performed aiming to validate the response of the system in monitoring the strains developed in steel beam elements subject to bending regimes. Representative results obtained from the above experimental tests have been included in this paper as well. KW - Structural health monitoring KW - strain sensors KW - strain gauges KW - bridges KW - steel and concrete structures Y1 - 2018 U6 - https://doi.org/10.1016/j.prostr.2018.09.005 SN - 2452-3216 VL - 10 SP - 25 EP - 32 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Rychkov, Dmitry A1 - Gerhard, Reimund A1 - Kuznetsov, Alexey A1 - Rychkov, Andrey T1 - Influence of charge density on the trap energy spectrum in fluoroethylenepropylene copolymer films with chemically modified surfaces JF - IEEE transactions on dielectrics and electrical insulation N2 - Tetrafluoroethylene-hexafluoropropylene copolymer (FEP) films were treated with titanium-tetrachloride vapor by means of molecular-layer deposition. The treatment leads to considerable improvements of the electret-charge stability on positively charged films. A slight improvement is also observed for negatively charged films. In line with our previous findings, we attribute the improvement in electret properties to the formation of deeper traps on the chemically modified polymer surfaces. Here, we investigate the influence of the charge density on electret stability of FEP films with modified surfaces. Trap-energy spectra obtained from thermally-stimulated-discharge measurements indicate that the charge stability on modified FEP films depends on how the surface traps are populated and on the availability of additional deeper traps. KW - Electrets KW - chemical modification KW - surface treatment KW - space-charge stability KW - charge-carrier transport KW - polytetrafluoroethylene (PTFE) KW - fluoroethylenepropylene (FEP) copolymer Y1 - 2018 U6 - https://doi.org/10.1109/TDEI.2018.007437 SN - 1070-9878 SN - 1558-4135 VL - 25 IS - 3 SP - 840 EP - 844 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Rychkov, Dmitry A1 - Altafim, Ruy Alberto Pisani T1 - Template-based fluoroethylenepropylene ferroelectrets with enhanced thermal stability of piezoelectricity JF - Journal of applied physics N2 - In ferroelectrets, the piezoelectricity stems from the charges of both polarities trapped on the inner surfaces of the cavities in the material, so that its thermal stability is defined by the stability of the respective charges. In the present work, a template-based lamination technique has been employed to fabricate tubular-channel ferroelectrets from fluoroethylenepropylene (FEP) films. It has been shown that the piezoelectricity in FEP ferroelectrets decays at relatively low temperatures due to the inherently lower thermal stability of the positive charge. In order to improve charge trapping, we have treated both FEP films and inner surfaces of the ferroelectret cavities with titanium-tetrachloride vapor, using the atomic-layer-deposition technique. Using surface-potential-decay measurements on FEP films, we have found that the charge-decay curves shift by more than 100 degrees C to the higher temperatures as a result of the surface treatment. Direct measurements of piezoelectric d(33) coefficients as a function of temperature have shown that the piezoelectric stability is likewise improved with the d(33)-decay curves shifted by 60 degrees C to the right. The improvement of electret/ferroelectret properties can be attributed to the formation of the deeper traps on the chemically modified FEP surface. SEM micrographs and EDS analysis reveal island-like structures with titanium- and oxygen-containing species that can be responsible for the deeper trapping of the electret charges. Published by AIP Publishing. Y1 - 2018 U6 - https://doi.org/10.1063/1.5041374 SN - 0021-8979 SN - 1089-7550 VL - 124 IS - 17 PB - American Institute of Physics CY - Melville ER -