Direct ink write multi-material printing of PDMS-BTO composites with MWCNT electrodes for flexible force sensors

With recent advances of additive manufacturing (AM) technology, direct ink write (DIW) printing has allowed to incorporate multi-material printing of various materials with freedom of design and complex geometric shapes to complete functional sensors in a one-step fabrication. This paper introduces the use of DIW 3D printing of polydimethylsiloxane (PDMS) with barium titanate (BTO) filler as stretchable composites with tunable piezoelectric properties that can be used for force sensors applications. To improve the bonding between stretchable piezoelectric composites and electrodes, multi-walled carbon nanotubes (MWCNT) was included in the fabrication of electrodes at a fixed ratio of 11 wt. %. The alignment of the BTO dipoles was achieved through corona poling method, which applies an electric charge on the surface layer of the functional material, aligning the dipoles in the desired direction and thus gaining the piezoelectricity. Different BTO mixing ratios (10-50 wt. %) were evaluated in order to obtain tunable piezoelectric properties and compare the sensitivity with respect their elastic properties. Tensile testing and piezoelectric testing were carried out to characterize mechanical and piezoelectric properties. Results showed that fabricated PDMS with 50 wt. % BTO gave the highest piezoelectric coefficient (d33) of 11.5 pC/N and with an output voltage of 385 mV under compression loading of >200 lbF. This demonstrates feasibility of using multi-material DIW printing to fabricate piezoelectric force sensors with integrated electrodes in one-step without compromising the flexibility of the material.

Peculiarities of ion-exchange in poled glasses

We demonstrate for the first time that the results of ion exchange processing of thermally poled soda-lime glass essentially depend on the poling conditions. In particular, the processing of vacuum-poled soda-lime glass in silver-sodium nitrate melt results in the diffusion and reduction of silver ions followed by clustering silver nanoparticles in the subsurface layer of the glass after either ion-exchange or additional heat treatment of the ion-exchanged samples. Poling in air atmosphere with deposited gold film anode prevents silver ions penetration in the glass, but electric field stimulated diffusion of gold in this configuration leads to the formation of gold nanoparticles in the glass after heat treatment. It is also shown that corona poling of the glass in air atmosphere does not completely block silver penetration.

Synergy of ferroelectric polarization and oxygen vacancy to promote CO2 photoreduction

Solar-light driven CO2 reduction into value-added chemicals and fuels emerges as a significant approach for CO2 conversion. However, inefficient electron-hole separation and the complex multi-electrons transfer processes hamper the efficiency of CO2 photoreduction. Herein, we prepare ferroelectric Bi3TiNbO9 nanosheets and employ corona poling to strengthen their ferroelectric polarization to facilitate the bulk charge separation within Bi3TiNbO9 nanosheets. Furthermore, surface oxygen vacancies are introduced to extend the photo-absorption of the synthesized materials and also to promote the adsorption and activation of CO2 molecules on the catalysts’ surface. More importantly, the oxygen vacancies exert a pinning effect on ferroelectric domains that enables Bi3TiNbO9 nanosheets to maintain superb ferroelectric polarization, tackling above-mentioned key challenges in photocatalytic CO2 reduction. This work highlights the importance of ferroelectric properties and controlled surface defect engineering, and emphasizes the key roles of tuning bulk and surface properties in enhancing the CO2 photoreduction performance.

Flexible Multiscale Pore Hybrid Self-Powered Sensor for Heart Sound Detection

This research introduces an idea of producing both nanoscale and microscale pores in piezoelectric material, and combining the properties of the molecular β-phase dipoles in ferroelectric material and the space charge dipoles in order to increase the sensitivity of the sensor and modulate the response frequency bandwidth of the material. Based on this idea, a bi-nano-micro porous dual ferro-electret hybrid self-powered flexible heart sound detection sensor is proposed. Acid etching and electrospinning were the fabrication processes used to produce a piezoelectric film with nanoscale and microscale pores, and corona poling was used for air ionization to produce an electret effect. In this paper, the manufacturing process of the sensor is introduced, and the effect of the porous structure and corona poling on improving the performance of the sensor is discussed. The proposed flexible sensor has an equivalent piezoelectric coefficient d33 of 3312 pC/N, which is much larger than the piezoelectric coefficient of the common piezoelectric materials. Experiments were carried out to verify the function of the flexible sensor together with the SS17L heart sound sensor (BIOPAC, Goleta, CA, USA) as a reference. The test results demonstrated its practical application for wearable heart sound detection and the potential for heart disease detection. The proposed flexible sensor in this paper could realize batch production, and has the advantages of flexibility, low production cost and a short processing time compared with the existing heart sound detection sensors.

Ferroelectric behavior in paracrystalline poly(vinyl trifluoroacetate)

Dielectric behavior in paracrystalline poly(vinyl trifluoroacetate) was investigated from the viewpoint of ferroelectricity. This polymer has a large CF3 dipole moment (2.3 Debye) and structural defects due to the atactic sequence in its chain conformation. It is possible to rotate the dipoles in paracrystals with defects under high electric field. The dielectric behavior was measured from 20 to 200 °C. A large dielectric constant and dielectric relaxation strength (Δε = 17 at 110 °C) were observed in the α-relaxation region. Corona poling on the samples was carried out at DC field 80 MV/m and 80 °C. Ferroelectric D–E hysteresis loop was observed under high electric field, and the remanent polarization and coercive field at 40 °C were 15 mC/m2 and 155 MV/m, respectively. Pyroelectric response and thermally stimulated current were measured from the current through the electrode irradiated by a pulsed semiconductor laser. A pyroelectric constant of about 6 μC/m2K was observed, which was stable up to near the poling temperature. The ferroelectricity in poly(vinyltrifluoroacetate) stems from the rotation of molecular chains in its paracrystals and orientation of the CF2 dipoles. Poly(vinyltrifluoroacetate) dielectrics can be used for capacitors with high power density, artificial skins, muscles and other flexible electronics.

Frequency dependent energy storage and dielectric performance of Ba–Zr Co-doped BiFeO3 loaded PVDF based mechanical energy harvesters: effect of corona poling

Corona poling improved the energy storage and mechanical energy harvesting performance of PVDF–Bi0.95Ba0.05Fe0.95Zr0.05O3 composite films.

Use of Flat Ribbon like Electrode Geometry to Pole PVDF Piezoelectrics in Solution Processing

We study how ribbons of fluids subjected to electric fields can serve applications in energy harvesting. In particular the emphasis is on how the geometry (i.e. 2-D ribbons) can influence functionality. For applications related to energy harvesting, we consider the use of polymer Piezo-electric PolyvinylideneFluoride (PVDF). Corona poling, photo-induced, photo-thermal and electron beam poling are the different conventional techniques used for PVDF poling. The parallel plate capacitor structure made for poling the PVDF material while the PVDF is being cured. One key advantage of preparing PVDF is the ability of solution processing. Normally, the liquid is then spin coated on a substrate and left to dry. Either during the process of spin coating, or after drying - the film of PVDF is poled so as to align the dipoles and make a piezoelectric. We propose the use of a metal-insulator ribbon like electrode geometry to combine the process of fabrication and poling thereby making the process more efficient. On the application of a voltage across the electrodes, the voltage of Vs is developed across the fluid. This result in a field of Vs/d across the PVDF fills aiding the process of poling while the film is in liquid phase. Therefore the ribbon like geometry aids the use of PVDF piezo-electrics in two ways. Firstly, it makes the fabrication process efficient by combining the poling with the structure development. Secondly, the control of width (w) and length (l) aids the setup of the PVDF piezoelectric resonant frequency for a given thickness (d). This helps match the resonant frequency of the ribbon with the incoming low frequency vibration to improve the energy harvesting levels. Piezo-electrics can be used in submerged applications, large area PVDF energy scavengers, mechanical filters and sensors, rural electrification, and charging circuits for hand-held devices.

Surface potential uniformity and sensitivity of large-area PTFE electret discs of different thicknesses produced by a modified corona poling rotating system for dosimetry applications

In this study, large-area (6-cm diameter) Teflon polytetrafluoroethylene (PTFE) discs of different thicknesses (0.2-, 0.5- and 1 -mm) were negatively and positively charged by using the “modified single point-to-plane corona poling rotating system”. The effects of some crucial parameters of the PTFE disc as well as the modified corona poling rotating system on the PTFE surface potential uniformity such as: (a) PTFE disc thickness, (b) PTFE disc polarity and (c) needle-to-PTFE disc distance were successfully reported. Accordingly, closer needle-to-PTFE disc distance, positive charging mode and thinner PTFE disc provided a better PTFE surface potential uniformity. However, the effects of PTFE charge polarity and needle distance on the electrostatic charge potential uniformity were much more remarkable in comparison with the effects of PTFE thickness. Additionally, the surface potential distribution profiles of charged PTFE discs were totally flat and independent of the PTFE thickness at 5- and 13-[Formula: see text]mm needle distances for the negative and positive charging modes, respectively. At the optimized charging conditions, large-area PTFE electret disc (0.5-mm-thick) with positive uniform surface charge potential especially at the edges up to [Formula: see text] 1.8[Formula: see text]kV with stability up to 77 days studied was produced by applying a new multiple heat treatment protocol to the PTFE disc for radon dosimetry. As also observed in this study, the sensitivity of PTFE electret dosimeters to a defined radon gas concentration increases as the PTFE thickness increases. Meanwhile, 0.5-mm-thick PTFE electret disc produced was selected to be used as a high quality electret dosimeter with acceptable and superior parameters for different applications in particular medium-term radiation dosimetry in both low and high dose rate ionizing radiation fields.