Development and Evaluation of Conducting Polymer Based Actuators

Transcription

1 Development and Evaluation of Conducting Polymer Based Actuators Clayton Bohn Brennan Research Group Materials Science & Eng Department University of Florida 2/18/03

2 Project Summary Develop and evaluate high performance actuators based on electroactive polymers (EAP s) Development of new method for measuring actuator performance Direct in situ strain measurement technique Enhance interlayer adhesion improved mechanical/actuation properties

3 constantan grid EAP Strain Measurement Techniques Method: Direct electrodeposition of CP s on strain sensitive substrate Benefits: Direct in situ measurements on commercially available substrates polyimide solder tabs ther Methods: Video capture Laser displacement Computer Function gen. Potentiostat Mechanical testing Disadvantages: Amp Everybody has different equipment Post processing required Detector

4 Conducting Polymers H H N N N N N N S S H H n H H n N H n PPy Highly cross-linked during synthesis High degree of strain Insoluble PEDP Stable to over oxidation High electrochemical cycle stability (> 40K) Aqueous compatibility of PEDP films PBEDT-Cz Low redox potential Three redox forms Presence of an irreversible oxidation peak at high potentials suggests a crosslinking Process (~1.15V)

5 Evaluations of EAP s PPy on PI strain gage scan rate = 10 mv/s in LiCl M water, E l = 0.4 V 3 Cyclic response of PPy actuation st cycle 2nd cycle 3rd cycle 4th cycle 5th cycle i (ma) Micro Strain (µε) E (V) versus A g /A g C l E(V) versus Ag/AgCl Micro Strain (µε) E (V) versus Ag/AgCl PPy, PEDP, & PBEDT- Cz E(V) versus Ag/AgCl Micro Strain (µε) PPy -0.8V to +0.4V PEDP -0.8V to 0V PBEDT-Cz -0.8V to +0.6V PBEDT-Cz -0.8V to +1.0V PBEDT-Cz -0.8V to +1.2V

6 PPy Adhesion to EvAu 10 µm 2 mm 20 µm A B C 50 µm PPy - CS delam Au µm PPy - CS delam Au 1 10 µm D E F

7 Advancing EAP s Problem: Actuation rate limited by diffusion and interlayer adhesion, defined by morphology Solution: Improve adhesion via structure/processing controlled morphology

8 Controlled Surface Morphology [4kX] 10 µm 10 µm 10 µm A EvAu/PI [0min] B EcAu/EvAu/PI [10min] C EcAu/EvAu/PI [60min] 10 µm 10 µm 10 µm D PPy/EvAu/PI [0min] E PPy/EcAu/EvAu/PI [10min] F PPy/EcAu/EvAu/PI [60min]

9 EcAu Deposition Charge 25 Roughness factor EcAu thickness 12 Surface Roughness (r) Nominal EcAu Thickness (µm) 0 r=a EC /A EcAu Deposition Charge (C/cm 2 )

10 Effects of S.R. and E.P.C. on Strain Surface Roughness (r) µε 200 µε 300 µε 400 µε 500 µε PPy (9.0 C/cm 2 ) on EcAu (r = 22.1) V 5 PPy (9.0 C/cm 2 ) on EvAu (r = 5.1) Electropolymerization Charge (C cm -2 )

11 Evaluations of Actuator Performance Actuator Lifetime Normalized Change in Strain Strain: EvAu (r = 3.43) Strain: EcAu (r = 8.26) Strain: EcAu (r = 18.0) Number of Redox Switches Normalized Change Frequency Response EvAu Strain (r=2.89) EvAu Charge EcAu Strain (r=10.00) EcAu Charge Frequency (Hz)

12 Evaluations of Actuator Performance Cont. 40 Effects of Polymerization Potential 0 Micro Strain (µε) Time (s) +0.7 V +0.8 V +0.9 V +1.0 V Micro Strain (µε) Effects of Stepping Potential Time (s) -0.6 V to +0.1 V -0.6 V to +0.2 V -0.6 V to +0.3 V -0.6 V to +0.4 V -0.6 V to +0.5 V -0.6 V to +0.6 V

13 EAP Linear Actuation Actuator Design: Variable PPy segment lengths control overall strain Actuator Model: Predicts 14.18% strain for 10mm PPy segments produced by a 1% strain in PPy PPy segment length (mm) Experimental strain (%) Calculated strain (%) Calculated strain based on a complete 1% strain in polypyrrole layer oxidation reduction oxidation reduction 10 mm segments Strain: 12.41% Voltage: -0.6 V to +0.6V 20 mm segments Strain: 23.84% Voltage: -0.6 V to +0.6V

14 New Linear Actuator Design ld design developed by alternating PPy placement on opposite sides of Au strip ne circuit design -all EAP is either oxidized or reduced x New actuator constructed with two circuit design to utilize both oxidation and reduction to develop linear actuation -ne side expands (x) while the adjacent side contacts (Red) By combining the EcAu surface treatment high strain linear actuators can be developed x Red

15 Conclusions and summary Strain gage methodology can provide detailed and continuous data on strain development in EAP s Strain response can be improved with the use of electrochemically deposited gold Linear actuation can be produced with proper EAP actuator configuration

16 Acknowledgements DARPA/AR grant DAAD Dr. Anthony Brennan Dr. John Reynolds Dr. Elisabeth Smela (Univ. of Maryland) Brennan Research Group Reynolds Research Group