Highly piezoelectric, thermal stable ferroelectrets from cyclic olefin copolymer Yan Li, Hui Wang, Changchun Zeng ANTEC 2015, Orlando
Content 1. Introduction 2. COC ferroelectret 3. Hybrid COC-PDMS ferroelectret
Problem Statement: 1. Introduction Need for a lightweight, low cost, high sensitivity and human-friendly wearable piezoelectric material based equipment Large demand of sensors made with non-toxic materials Lack of movement flexibility of traditional piezoelectric materials > Present market for printed and flexible sensors is $140 million > Market in 2023 will be over $1 billion
Comparison of piezoelectric coefficients of several piezoelectric materials Piezoelectric material Crystal: Quartz (silicon dioxide) Ceramic: Lead zirconate titanate (PZT) Ferroelectrics: β-phase polyvinylidene (β-pvdf ) Ferroelectret: optimized cellular polypropylene (PP) d 33 (pc/n) 2 (d 11 ) 170-600 20 600 PZT does not has the polymer advantages (softness and light-weight) PVDF low piezoelectric activity PP low applied temperature (-20 o C ~ 50 o C) limits their usefulness
Ferroelectrets Ferroelectrets, are space-charged porous polymers with significant piezoelectricity d Q F V The cellular voids with charges of opposite sign on the upper and lower walls form macroscopic dipoles. The effective dipole moment changes under mechanical stress and gives rise the piezoelectricity
Benefits of Ferroelectrets High sensitivity, high enough to be embedded into pressure management devices Non-toxic, crucial when materials be used with human direct contact Flexible, enables large movement detection of the sensor Low cost, very low cost compare to traditional piezoelectric materials Lightweight, high energy harvesting efficiency A curved sensor array made by piezoelectric foam Piezoelectric foams sensor attached to human body
Problem in current commercial ferroelectrets Cellular polypropylene (PP) film High piezoelectric coefficient of ~ 1000 pcn -1, but very low operation temperature (<60 o C), due to the poor charge storage stability of PP. Develop new thermally stable polymer ferroelectrets. polytetrafluoroethylene fluorinated ethylene propylene polyethylene terephthalate (PET) polyethylene naphthalate (PEN ) polycarbonate (PC) polyetherimide (PEI) cyclo-olefin copolymers (COCs)
Cyclo-olefin Copolymer (COC) a x y COC meets all these requirements: I. Low water absorption, < 0.01% II. High electrical resistivity, >10 13 Ω cm COC is superior to any known positively charged polymer (PET, PEN, FEP, PTFE, PETP, etc.)
Low piezoelectric activity However, d 33 of COC ferroelectrets are reported typically in the range: 10-20 pc/n.
OUR GOAL Develop Thermally Resistant, High Sensitive Polymer Based Piezoelectric Materials based on: 1. Introduction >Promising candidate materials 2. COC ferroelectret Cyclic Olefin Copolymers (COCs) Highly Thermally Stable, Excellent Charge Capacity, Thin, Lightweight, Water Resistant, and Flexible 3. Hybrid COC-PDMS ferroelectret >Novel fabrication technology
1. Introduction 2. COC ferroelectret 3. Hybrid COC-PDMS ferroelectret
2. COC ferroelectrets of high piezoelectricity Structure Design 1 d33 K E eff Li, Y., Zeng, C. Macromolecular Chemistry and Physics 2013, 214, 2733-2738. The basic mechanism in the novel COC ferroelectrets is simple: allow the multilayer structure to bending.
Schematic of the fabrication process b Laser cutting machine 1 Laser 2 metallised COC film patterned COC film central COC film patterned COC film metallised COC film 4 Charging 3 CO 2 bonding F, co 2 Charging equipment Very low bonding temperature (120 o C) A multi-layer COC films with a multipoint short-beam structure by combining laser cutting and carbon dioxide bonding techniques. High pressure vessel
b Deformation ( m) 0-2 -4-6 -8 w = 1 mm w =1.5 mm w = 2 mm w = 2.5 mm -10 w = 3 mm -12-20 -15-10 -5 0 5 10 15 20 Position (mm) Finite element modeling results of the overall deformation in the thickness direction of the COC ferroelectrets with different geometry.
Deformation ( m) c 20 15 1 mm 2 mm 3 mm 10 5 0 0 5 10 15 20 P (kpa) Simulated deformation (in thickness direction) of COC ferroelectrets with different design under a series of pressure showing excellent linear response.
c 460 440 420 T g (K) 400 380 360 340 320 0 5 10 15 20 25 30 CO 2 Pressure (MPa)
Piezoelectric Activity a d 33 (pc/n) 10 4 10 3 10 2 10 1 2.5 mm 3 mm 2 mm 3 mm (no overlap) 1.5 mm 15 pc/n 10 0 0 5 10 15 20 Applied pressure (kpa) The control of geometry structure allow a direct adjustment of piezoelectric activity
Thermal Stability b 1.0 Normalized d 33 0.8 0.6 0.4 0.2 Short-term test 0.0 0 20 40 60 80 100 120 140 160 180 Temperature ( o C) The piezoelectric d 33 coefficients of samples only exhibited a slight decay after a thermal treatment at 40-120 o C.
c 1.0 Normalized d 33 0.8 0.6 0.4 0.2 Long-term test 0.0 0 25 50 75 100 125 150 175 200 Time of thermal treatment (h) The retained d 33 coefficient only drops to 70 % of the initial value annealing at 110 o C for 200 h.
Current (pa) Thermal Stimulated Discharge 80 60 40 20 0 50 100 150 200 250 Temperature ( o C)
Polarization (uc/cm2) Hysteresis loop 0.08 0.06 0.04 0.02 0.00-0.02 Polarization (500V) Polarization (1000V) Polarization (1500V) Polarization (2000V) Polarization (2500V) Polarization (3000V) Polarization (4000V) Polarization (5000V) Polarization (6000V) Polarization (7500V) -0.04-0.06-0.08-8000 -6000-4000 -2000 0 2000 4000 6000 8000 Voltage (volt)
Quasi-permanent Polarization (uc/cm2) Piezoelectric Coefficient (pc/n) 0.014 Quasi-permanent Polarization (at 4.9kPa) Piezoelectric Coefficient (at 4.9kPa) 1600 0.012 1400 0.010 0.008 0.006 1200 1000 800 600 0.004 400 0.002 200 0.000 0 1 2 3 4 5 6 7 8 9 10 Applied voltage (kv)
Displacement (micron) Actuation behavior 0.10 0.08 0.06 0.04 0.02 0.00-0.02-0.04-0.06-8000 -6000-4000 -2000 0 2000 4000 6000 8000 Drive Voltage (volt)
Current (pa) Quasi-permanent Polarization (uc/cm2) Piezoelectric Coefficient (pc/n) Effect of different types of COC 0.016 0.014 0.012 0.010 0.008 0.006 2000 1500 1000 6017 6013 8007 0.004 0.002 0.000-0.002 6017 6013 8007 0 2 4 6 8 10 Applied Voltage (volt) 500 0 0 5 10 15 20 25 Applied Pressure (kpa) 120 100 80 6017 6013 8007 60 40 20 0 50 100 150 200 250 Temperature ( o C)
Piezoelectric Coefficient (pc/n) Structure Design 2 Eye-shape structure 7000 6000 5000 4000 3000 2000 1000 0 0 5 10 15 20 25 Applied Pressure (kpa)
1. Introduction 2. COC ferroelectret 3. Hybrid COC-PDMS ferroelectret
3. Hybrid ferroelectrets: sandwich structure with rubber layers
Electric output of a typical COC-PDMS ferroelectret
Compression force (N) Photograph of the test set-up 50 40 30 20 10 0 0 10 20 30 40 50 Time (s) Compression force under cycling compression at a given compression rate 20 mm/min
Open-Circuit Voltage (V) Short-Circuit Current (na) 25 3 20 2 15 1 10 0-1 5-2 0 0 10 20 30 40 50 Time (s) -3 0 10 20 30 40 50 Time (s) Measured open- circuit voltage and short- circuit current under cycling compression
Voltage (V) Images of a commercial red LED in dim background before and the moment of being lit up by the storage energy. Circles 0 100 200 300 400 500 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 200 400 600 800 1000 1200 Time (s) The charging curve across a single capacitor when pumped by a under cycling compression test, showing a steady increase in the storage charge charges with the increase of charging time.
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