Development of Piezoelectric Nanocomposites for Energy Harvesting and Self- Kenneth J. Loh Assistant Professor Department of Civil & Environmental Engineering University of California, Davis The Applied Power Electronics Conference and Exposition Special Presentations Palm Springs, CA February 23, 21
Motivation for Structural Health Monitoring Structural systems susceptible to various types of structural damage: Excessive loading and natural hazards (e.g., earthquakes, wind, among others) Fatigue cracking Corrosion and stress-corrosion cracking Damage diminishes structural performance, reliability, and safety Urgent need for long-term sensing technologies to prevent catastrophic structural failure Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 2/17
Current Inspection Approaches National Bridge Insp. Program: Bi-annual inspection Inspections are generally visual Challenges of visual inspection: Subjective with rating variability Limited to accessible locations Expensive and labor intensive Permanent monitoring systems reserved for critical structures: Cable-based monitoring systems High installation costs: $3, (US) per channel Lower sensor densities are poorly scaled to damage Simple Sensor (e.g. accelerometer) Central Data Repository Typical bridge inspection with crane Cable-based structural monitoring system Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 3/17
Emerging Technologies Wireless Sensors and Sensor Networks Micro-electromechanical Systems (MEMS) Carbon Nanotube (CNT)- based Thin Films WiMMS Wang, et al. (28) Intel Imote2 Spencer, et al. (27) AD imems Weinberg (1999) 3-axis accelerometer Lemkin (1997) CNT buckypaper Prasad, et al. (24) CNT Neuron sensor Kang, et al. (26) Advantages: Low cost Dense instrumentation Reconfigurable Advantages: Miniaturized sensor designs Lower power consumption Complex sensors/actuators Advantages: Multifunctional by nature Bottom up assembly Conformable Disadvantages: Disadvantages: Disadvantages: Point sensors Major drawbacks of these emerging Top-down technologies: design Technology at its infancy Indirect damage detection Expensive fabrication Scalability Power demand: require constant power supplies (e.g., batteries or AC power) Physics-based models equipment High costs of nanomaterials High costs* Sensor sensitivity on par with macro-scale counterpart Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 4/17
Piezoelectric Materials Generation of electric potential due to strain Strain Piezoelectric Materials Lead zirconate titanate (PZT) Poly(vinylidene fluoride) (PVDF) Rectifier Storage Piezoelectric energy harvester Electric potential Strain generation due to electric field MFC piezoelectric actuator Piezoelectricity is the transduction between mechanical and electrical energies Objective of this research: Direct piezoelectric effect: Developa Generation piezoelectric of electrical nanocomposite potential due that to applied exhibits strain high (energy piezoelectricity harvesting and sensing) Inverse mechanical piezoelectric flexibilityeffect: Generation of applied strain due to applied electrical potential (actuation) Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 5/17
Zinc Oxide Nanoparticles & Nanowires Zinc oxide (ZnO) nanoparticles and nanowires: Wide band gap (~ 3.4 ev) II-VI semiconductor High electron mobility Inherently piezoelectric Wurtzite asymmetrical crystal structure Relative displacement of Zn 2+ with respect to O 2- during applied strain Wurtzite crystal structure Zinc oxide nanoparticles Ni, et al. (27) ZnO piezoelectricity under different strain modes Gao, et al. (29) Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 6/17
Fabrication Methodology Numerous techniques for fabricating ZnO-based thin films: Sputtering, chemical vapor deposition, as-grown nanowire arrays, among others Suffer from high fabrication costs, scalability, and limited thicknesses Fabrication based on thermal annealing and evaporation: ZnO-PSS-PVA thin film (a) Non-dispersed and (b) dispersed ZnO-PSS solutions Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Low-temperature thermal evaporation Slide 7/17
Thin Film Morphology Utilize scanning electron microscopy to qualitatively evaluate deposited nanoparticle dispersion and density Pristine zinc oxide average particle diameter of 2 nm Observe adequate dispersion and dense deposition of nanoparticles Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 8/17
Piezoelectricity Experimental Setup Experimental validation of ZnO-PSS-PVA thin film piezoelectricity: Affix nanocomposite onto Plexiglas cantilever beam Instrumented P(VDF-TrFE) piezoelectric polymer as control Simultaneously measured generated voltage when beam undergoes free vibration ZnO-PSS-PVA and PVDF film affixed onto Plexiglas cantilevered beam Generated potential measured using Agilent 54621D oscilloscope Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 9/17
Nanocomposite Piezoelectricity Free vibration of beam induced by introducing large initial displacement Strain gage near support measures strain at top surface of beam ZnO-PSS-PVA thin film piezoelectricity compared to commercial P(VDF-TrFE) Validated piezoelectric response of proposed thin film Exhibited comparable piezoelectricity with commercial P(VDF-TrFE) films 8 6 4.4.3.2.1 PVDF ZnO-PSS Strain [µε] 2 Voltage [V] -.1-2 -.2 -.3-4 -.4-6.1.2.3.4.5.6 Time [s] -.5.5.1.15.2.25.3.35.4 Time [s] Flexural strain of beam during free vibration Overlay of ZnO-PSS and P(VDF-TrFE) thin film generated voltage Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 1/17
Strain Experimental Validation Self-sensing strain sensor validation study: Direct piezoelectric effect Does not depend on external power supply (e.g., batteries or AC power) Self-sensing performance evaluated using free vibration of cantilevered beam Magnitude of generated voltage directly related to induced strain -.75 -.5 Strain 7,5 5, -.25 2,5 Voltage [V] Strain [µε].25-2,5.5-5, ZnO-PSS-PVA films affixed onto PVC beam ZnO-PSS.75.5.1.15.2.25.3.35-7,5.4 Time [s] Overlay of ZnO-PSS-PVA voltage response v. applied strains Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 11/17
Optimization of Piezoelectricity Optimize piezoelectric performance based on zinc oxide weight fraction, f film : f film = w ZnO w + w ZnO PSS + w PVA 1% Fabricate 16 unique types of thin films: Varied ZnO concentration in PSS solution Varied PSS dipersing agent s concentration Fixed 1. wt.% poly(vinyl alcohol) solution concentration 1. wt.% PSS 2.5 wt.% PSS 5. wt.% PSS 1 mg-ml -1 ZnO in PSS Sample A: 33.3% Sample E: 22.2% Sample I: 14.3% 2 mg-ml -1 ZnO in PSS Sample B: 5.% Sample F: 36.4% Sample J: 25.% 3 mg-ml -1 ZnO in PSS Sample C: 6.% Sample G: 46.2% Sample K: 33.3% 4 mg-ml -1 ZnO in PSS Sample D: 66.7% Sample H: 53.3% Sample L: 4.% Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 12/17
Comparison of Bulk Film Piezoelectricity Simultaneously measured thin film generated voltages during free vibration of the cantilevered beam Results show only certain films exhibit good piezoelectric performance Optimal ZnO weight fraction is approximately 33% to 37% High ZnO weight fraction thin films have high noise floors due to agglomeration [mv-cm] [mv-cm] [mv-cm] [mv-cm] [mv-cm] 1 25 Sample F.75 2-1 Sample E.5 15 1 1.5 2 2.5 3 1.25 5-1 Sample F 1 1.5 2 2.5 3 1-5 Sample G -.25-1 1 1.5 2 2.5 3-15 1 -.5-2 -1 Strain Sample rateh -25 -.75 1.4 1 1.6 1.5 1.8 2 2 2.52.2 2.43 Time [s] [s] Strain rate [ ε-s -1 ] [mv-cm] [mv-cm] [mv-cm] [mv-cm] [mv-cm] 4 15 1 2 Sample K -2.75 Sample I -4 1 1 1.5 2 2.5 3 4.5 2 5.25-2 Sample J -4 1 1.5 2 2.5 3 4 2 -.25-2 -5 Sample K -4 1 1.5 2 2.5 -.5 3 4-1 2 -.75-2 Sample L -4 Strain rate -15 1.5 1 1.7 1.5 1.9 2 2.1 2.5-1 2.3 2.53 Time Time [s] [s] Strain rate [ ε-s -1 ] Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 13/17
Layer-by by-layer Thin Film Fabrication Sequential assembly of oppositely-charged nanomaterials onto a charged substrate Bottom-up fabrication methodology Incorporation of a wide variety of nanomaterials 2.5-dimensional nano-structuring to design multifunctional composites Excellent physical, mechanical, and electrical properties: Enhance thin film homogeneity Alignment of zinc oxide nanowires in polymeric matrix 2. Polyanionic monolayer ZnO Nanowires-PSS 1. Polycationic monolayer PVA, PANI, etc. Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 14/17
Poling and Molecular Alignment Current piezoelectric materials undergo high-voltage poling during fabrication: Alignment of molecular dipole moments to elicit high piezoelectricity ZnO-based nanocomposites do not need poling to attain piezoelectricity: Future work: employ high voltage (kv) poling to further enhance nanocomposite performance Poling Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 15/17
Summary of Results & Path Forward Zinc oxide nanoparticles as a viable novel material for the development of piezoelectric nanocomposites: ZnO inherently piezoelectric Dispersed in polyelectrolyte solutions Thermal annealing and evaporation for thin film fabrication Preliminary results confirm ZnO-PSS-PVA thin film piezoelectricity: Affixed nanocomposites to cantilevered Plexiglas and PVC beams Measured generated potential under free vibration of the beam Validated comparable piezoelectricity with commercial PVDF-based films Optimized zinc oxide weight fraction to find optimal 33% to 37% concentrations Future research directions: High-electric field poling to further enhance piezoelectricity Generated potential can find applications in ambient energy harvesting Need to enhance its electrical and mechanical properties for actuation/active sensing Development of Piezoelectric Nanocomposites for Energy Harvesting g and Self- Slide 16/17
Thank You! QUESTIONS? Acknowledgements: This research is supported by the College of Engineering, University of California, Davis The authors would also like to express their gratitude to: Ms. Yingjun Irene Zhao (M.S. Student): Piezoelectric testing Mr. Donghyeon Ryu (Ph.D. Student): SEM imaging Ms. Donghee Chang (Undergrad): Nanocomposite fabrication