Data for the publication: Biomimetic microfractals based flexible triboelectric nanogenerators

README: Schematic overview of the fabrication process of the BM-TENG. Figure 1. Shows the schematic illustration of the overall fabrication process of the BM-TENG. (a) Fabrication of conductive leaf skeleton as current collectors using dip coating method (b) Fabrication of biomimetic triboelectric layers on top of current collector using customized electrospinning method (c) Schematic of the layers of BM-TENG and digital photograph of the BM-TENG. The schematic was drawn by Amit Barua. The camera image was captured by Amit Barua. SEM images of different layers of the BM-TENG. Figure 2. SEM images of the Rubber (Hevea brasiliensis) leaf skeleton and biomimetic surface of rubber leaf skeleton. (a) Real leaf skeleton of rubber tree (b) CuNWs-coated conductive rubber leaf skeleton used as current collector layer (c) Biomimetic rubber leaf skeleton surface made with Nylon 6 polymer used as tribopositive layer (d) Biomimetic rubber leaf skeleton surface made with Polyvinylidene Fluoride (PVDF) polymer used as tribonegative layer. The SEM images were taken by Rituporn Gogoi and Amit Barua. Characterization of conductive surfaces as current collectors for the BM-TENG. Figure 3. Current collector surface characterization. (a) Histogram showing resistance of the rubber leaf skeleton with respect to the number of dipping cycles. (b) Conductivity mapping showing uniform sheet resistance after CuNWs loading on rubber leaf skeleton surface. (c) Cyclic test of 1000 bending cycles vs relative resistance of the leaf-based current collector at a frequency of 0.083 Hz. Inset shows relative resistance of the biomimetic current collector throughout one full cycle of bending. (d) Digital image of biomimetic current collector loaded with 60 µg cm−2 of CuNWs. (e) Digital image of CuNWs coated PVDF nanofiber surface with equal loading quantity of 60 µg cm−2 CuNWs. (f) Digital image of CuNWs coated PVDF nanofiber surface with double loading quantity of 120 µg cm−2 CuNWs. The sheet resistance, Rs values and the loading concentration of CuNWs are mentioned with the respective digital images in d, e and f. (g) SEM image of CuNWs coated rubber leaf skeleton surface (h) SEM image of CuNWs coated PVDF nanofiber surfaces with equal amount of loading quantity of the rubber leaf. (i) SEM image of CuNWs-coated PVDF nanofiber surfaces with double the loading quantity of the rubber leaf. Inset of each SEM image represents a magnified version of the image in g, h, and i. The dip coating experiments, conductivity mapping and cyclic bending test were performed by Amit Barua. Photographs were collected by Amit Barua and Ana-Marija Pitner. Fabrication of CuNWs coated PVDF nanofiber films was performed by Ana-Marija Pitner. Simulation comparison studies of CuNW networks on planar surfaces and biomimetic surfaces. Figure 4. Simulation study of sheet resistance in CuNWs networks interfaced with planar surfaces (random network of CuNWs) and biomimetic surfaces (directional network of CuNWs). Depiction of (a) Random network angle probability p(Φ), which is the same for all angles, and (b) Directional network defined by mean direction angle <Φ> and standard deviation of direction angle 𝜎Φ. CuNWs networks with (c) Random structure, (d) Directional structure, and (e) Bundled directional structure at 20% area. (f) Impact of standard deviation of direction angle 𝜎Φ on sheet resistance. (g) Impact of bundling area on sheet resistance. (h) Influence of mass density on the impact of bundling and directionality. All the simulation studies were performed by Mislav Matić and Mirko Poljak. Electrical characterization of the BM-TENG. Figure 5. Electrical characterization of the BM-TENG. (a) Representative schematic diagram of the test setup. (b) Schematic of the BM-TENG layers highlighting positive and negative charges of the biomimetic triboelectric layers. (c) Typical mechanism of the BM-TENG. (d) Current density comparison between planar TENG and the BM-TENG considering projected area. (e) Open-circuit voltage, VOC measurement of BM-TENG at different pressures. (f) Histogram plot of mean peak-to- peak VOC. Error bars represent the standard deviation. (g) Short-circuit current ISC measurement of BM-TENG at different pressures. (h) Histogram plot of mean peak-to-peak ISC. Error bars represent the standard deviation. (i) Current density of the planar control TENG considering projected area. (j) Current density of the BM-TENG considering projected area. (k) Current and voltage measurement for BM-TENG with respect to different load values from 1 kΩ to 100 MΩ. (l) Power density calculation of the planar control TENG with projected area, BM-TENG with projected area, and BM-TENG with effective surface area of leaf skeleton processed by ImageJ. Here, Pressure 1 = 20 kPa, Pressure 2 = 300 kPa, Pressure 3 = 1 MPa and Pressure 4 = 2.5 MPa. All the electrical characterizations were performed by Amit Barua. Demonstration of the BM-TENG. Figure 6. Application and demonstration experiments of the BM-TENG. (a) Schematic of current and potential applications of the BM-TENG. (b) Cyclic voltage measurement test with repeated tapping at 5.45 Hz frequency and 1 MPa pressure for ∼10000 cycles. (c) Lighting up 22 LEDs making a University of Turku (UTU) logo with simultaneous tapping cycles. (d) Charging and discharging rate of a 1 µF capacitor with tapping cycles. (e) Charging rate of different capacitors of capacitance values 0.1, 1, and 10 µF. (f) BM-TENG attached to the elbow showing voltage output during elbow motion. (g) BM-TENG attached to the wrist showing voltage output during periodic wrist bending. (h) BM-TENG mounted on a wall switch showing voltage output under repeated tapping. (i) Voltage output under foot-tapping excitation. (j) Digital photographs of the BM-TENG attached to a robotic gripper for grip sensing. Upper image shows the BM-TENG integrated onto the robotic gripper, while the lower image shows the gripper holding an object during the sensing operation. (k) Signal response of the gripping and releasing cycles visualized through a digital oscilloscope. (l) Digital photograph of the breath monitoring setup and demonstration. (m) Signal response of the breathing cycles visualized through a digital oscilloscope. (n) Notification of breath cycle detection and BPM value in an Android-based mobile application connected via Bluetooth. All the demonstration experiments were performed by Amit Barua, Aman Kumar and Anastasia Koivikko. Optical microscopic image of the rubber leaf skeleton. Figure S1. Optical microscopic images of rubber leaf skeleton. a) Normal image b) Image converted to greyscale using ImageJ software. The images were captured and analyzed by Amit Barua. BM-TENG performance at different frequencies. Figure S2. Open circuit voltage and short circuit current output performance of the BM-TENG at different frequencies. a) Open circuit voltage characteristics of the BM-TENG at frequencies 0.5 Hz, 1 Hz, 1.5 Hz and 2 Hz. b) Short circuit current characteristics of the BM-TENG at frequencies 0.5 Hz, 1 Hz, 1.5 Hz and 2 Hz. The tests were performed by Amit Barua. BM-TENG performance with finger tapping conditions. Figure S3. Voltage and current output performance of the BM-TENG at different pressure having a 10 MΩ load with finger tapping. a) Voltage measurement at different pressures b) Histogram plot of mean voltage at different pressures. Error bars represents the standard deviation. c) Current measurement at different pressures d) Histogram plot of mean current at different pressures. Error bars represents the standard deviation. The tests were performed by Amit Barua. Breathability test of the BM-TENG. Figure S4. Breathability test of the full BM-TENG device. a) Air permeability test from 50 – 500 Pa pressure drop. The test area was 20 cm2 b) Water vapour transmission rate test for the BM-TENG device. The test area was 2 cm2 and test conditions were 50% relative humidity and 23 °C. The tests were performed by Measurlabs Oy, Helsinki, Finland. Voltage characterization of the BM-TENG without encapsulation layer. Figure S5. Voltage characterization of the full BM-TENG without the encapsulating protective layer. a) Open circuit voltage at different pressure values. b) Cyclic test of voltage at pressure 1 MPa. The characterization was performed by Amit Barua. All electrical characterizations for four different TENG devices consisting of three control devices and one BM-TENG. Figure S6. Open circuit voltage for all four TENG devices. a) Open circuit voltage of control device 1 (full planar TENG) at different pressures. b) Open circuit voltage of control device 2 (planar collector biomimetic tribolayer TENG) at different pressures. c) Open circuit voltage of control device 3 (biomimetic collector planar tribolayer TENG) at different pressures. d) Open circuit voltage of full BM-TENG at different pressures. Pressure 1 = 20 kPa, Pressure 2 = 300 kPa, Pressure 3 = 1 MPa, Pressure 4 = 2.5 MPa. Figure S7. Short circuit current for all four TENG devices. a) Short circuit current of control device 1 (full planar TENG) at different pressures. b) Short circuit current of control device 2 (planar collector biomimetic tribolayer TENG) at different pressures. c) Short circuit current of control device 3 (biomimetic collector planar tribolayer TENG) at different pressures. d) Short circuit current of full BM-TENG at different pressures. Pressure 1 = 20 kPa, Pressure 2 = 300 kPa, Pressure 3 = 1 MPa, Pressure 4 = 2.5 MPa Figure S8. Current density for all four TENG devices. a) Current density of control device 1 (full planar TENG) at different pressures. b) Current density of control device 2 (planar collector biomimetic tribolayer TENG) at different pressures. c) Current density of control device 3 (biomimetic collector planar tribolayer TENG) at different pressures. d) Current density of full BM-TENG at different pressures. Pressure 1 = 20 kPa, Pressure 2 = 300 kPa, Pressure 3 = 1 MPa, Pressure 4 = 2.5 MPa Figure S9. Voltage, current and power with different load resistance for all four TENG devices. a) Maximum voltage and current vs load resistance curve of control device 1 (full planar TENG). b) Maximum power density vs load resistance curve of control device 1. c) Maximum voltage and current vs load resistance curve of control device 2 (planar collector biomimetic tribolayer TENG). d) Maximum power density vs load resistance curve of control device 2. e) Maximum voltage and current vs load resistance curve of control device 3 (biomimetic collector planar tribolayer TENG). f) Maximum power density vs load resistance curve of control device 3. g) Maximum voltage and current vs load resistance curve of full BM-TENG). h) Maximum power density vs load resistance curve of full BM-TENG. All the characterizations were performed by Amit Barua. Performance of the BM-TENG at different curvature. Figure S10. Curvature vs Voltage test for the full BM-TENG device. The peak represents the mean value and error bars represents the standard deviation. The characterization was performed by Amit Barua. BM-TENG demonstration as MORSE code generator. Figure S11. BM-TENG demonstration as MORSE code generator and wireless transmission of the message through mobile application. a) Digital photograph of the BM-TENG connected to a full-bridge rectifier and then to Morse encoder circuit. b) Visualization of the decoded MORSE code message in android based mobile application connected via Bluetooth. c) Rectified signals created by the BM-TENG to encode a ‘HELP’ message which is fed to the MORSE encoder circuit. d) Magnified version of the signals to create four dot signals to encode the letter ‘H’. e) Magnified version of the signals to create one dot, two dashes and one dot signals to encode the letter ‘P’. Here, the voltage signal pairs having <300 ms time gap are considered a ‘dot’ and the voltage signal pairs having time gap between 300 ms to 1500 ms are considered a ‘dash’. This translation is performed by Arduino programming. The demonstration was performed by Amit Barua and Aman Kumar. Supplementary Video S1. Lighting up 22 LEDs with simultaneous tapping cycles on the BM-TENG. The LEDs are arranged in a specific design to make a University of Turku (UTU) logo. The experiment and video were recorded by Amit Barua and Aman Kumar. Supplementary Video S2. BM-TENG attached to the wrist showing voltage output variation during periodic wrist bending movement. The experiment and video were recorded by Amit Barua and Aman Kumar. Supplementary Video S3. BM-TENG attached to the elbow showing voltage output variation during elbow movement. The experiment and video were recorded by Amit Barua and Aman Kumar. Supplementary Video S4. BM-TENG attached to a robotic gripper for grip sensing. Signal response of the gripping and releasing cycles visualized through a digital oscilloscope. The experiment and video were recorded by Amit Barua and Anastasia Koivikko. Supplementary Video S5. BM-TENG attached to a face mask for breath monitoring experiment and wireless transmission of the signal through mobile application. Signal response of the breathing cycles visualized through a digital oscilloscope. The experiment and video were recorded by Amit Barua and Aman Kumar. Supplementary Video S6. BM-TENG demonstration as MORSE code generator and wireless transmission of the message through mobile application. The experiment and video were recorded by Amit Barua and Aman Kumar. ____________