Fabrication and characterization of microporous carbon-based electroactive polymer actuators
Date
2012-07-09
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Abstract
Elektroaktiivsed polümeerid (EAP) on modernsed materjalid, mis muundavad elektrilise energia mehaaniliseks deformatsiooniks või vastupidises suunas, leides seega rakendust nii aktuaatorite kui sensoritena. Elektroaktiivsed polümeerid omavad kõrget potentsiaali funktsionaalsete materjalidena arendamaks uusi üha kasvava nõudlusega aktuaatorite süsteeme, mis on vaiksed, elastsed, kerged, struktuurilt lihtsad ja lihtsasti miniaturiseeritavad. Biorobootika rakendusteks on atraktiivsed eelkõige ioonset tüüpi EAP-d, mis koosnevad elektrolüüti sisaldavast membraanist ja kahest elektrit juhtivast elektroodikihist selle pindadel.
On teada, et suurendades laengutihedust elektroodides, pareneb aktuaatori liigutussuutlikkus. Sellest lähtuvalt uuriti antud töös kõrge eripinnaga poorseid elektroodimaterjale aktuaatorite valmistamiseks. Suurimat potentsiaali omavad antud vallas suure poorsusega amorfsed süsinikud ja karbiidset päritolu süsinikud, mida tavaliselt kasutatakse energiasalvestus-seadmetes – superkondensaatorites. Süsinikaerogeelid on samuti paljulubavad materjalid EAPdes rakendamiseks.
Käesolevas töös uuriti nelja erinevat poorset süsinikmaterjali (karbiidne süsinik, kookospähklikoorest valmistatud aktiveeritud süsinik ning aktiveeritud ja mitteaktiveeritud süsinikaerogeelid) uute alternatiividena EAP aktuaatorite elektroodides. Vastavaid elektroodimaterjale analüüsiti viiekihilistes aktuaator-süsteemides, mis koosnesid 1-etüül-3-metüülimidasoolium trifluorometaansulfonaat (EMI-TF) ioonvedelikus immutatud Nafion-membraanist kahe süsinikelektroodi vahel ja kuldfooliumist selle välispindadel. Uuriti valmistatud EAP aktuaatorite elektromehaanilisi, elektrokeemilisi ja mehaanilisi karakteristikuid ning võrreldi neid aktuaatoritega, mis baseerusid RuO2-elektroodidel. Karbiidsest süsinikust elektroodidega EAP aktuaator omas suurimat liigutusulatust (painde deformatsiooni) uuritud elektroodimaterjalide seas. Maksimaalseks painde deformatsiooniks osutus 2,04% ±2 V ristkülikpinge sisendi korral, mis ületas RuO2-elektroodidel põhineva aktuaatori liigutusulatust rohkem kui kaks korda. Tulemuste analüüs näitas, et EAP aktuaatorite elektromehaanilised karakteristikud on tugevalt sõltuvad süsinikmaterjalide poorsetest omadustest ja struktuursest jäikusest (st. grafitiseerituse astmest).
Üheseinaliste süsiniknanotoru lisandite mõju aktuaatori liigutusomadustele uuriti kolmekihilistes aktuaator-süsteemides, mis koosnesid polümeriseeritud 1-etüül-3-metüülimidasoolium tertrafluoroboraadi (EMI-BF4) elektrolüüdikihist kahe nanotorusid ja karbiidset süsinikku sisaldava elektroodi vahel. EAP aktuaatorite valmistamiseks kasutati elektroode, mis sisaldasid süsiniknanotorusid karbiidses süsinik-elektroodis viies erinevas vahekorras ning uuriti nende elektromehaanilisi, elektrokeemilisi ja mehaanilisi omadusi. Tulemuste analüüs näitas, et süsiniknanotorude sisalduse suurendamine komposiitelektroodides parandas oluliselt elektroodide elektrilist juhtivust ning suurendas nende mehaanilist jäikust (Young`i moodulit). Süsiniknanotorude lisamine elektroodidesse suurendas märkimisväärselt aktuaatori liigutussuutlikkust. Madalatel liigutussagedustel (5 mHz–0,5 Hz) oli aktuaatoril, mille elektroodid sisaldasid võrdses koguses nanotorusid ja karbiidset süsinikku (50/50 massi%), oluliselt suurem liigutusulatus (deformatsioon 0,85%) antud töös uuritud aktuaatorite seas. See ületab puhtast karbiidsest süsinikust elektroodidega aktuaatori liigutusulatust (0,35%) rohkem kui kaks korda. Leiti, et erimahtuvus ja Youngi moodul omavad tugevat koosmõju aktuaatori liigutusulatusele madalamas liigutussagedusalas, kus ilmnevad ka aktuaatorite elektrienergiat salvestavad omadused.
Electroactive polymers (EAPs) are a type of smart materials that convert electrical pulse energy into mechanical deformation or vice versa, and hence, can be utilized as actuators or sensors. EAPs are promising functional materials for engineering new and increasingly demanded actuation systems that are silent, mechanically compliant, lightweight, structurally simple, and easily scalable. Ionic type of EAPs that consist of electrolyte containing membrane between two conductive electrode layers are especially attractive for bio-robotic applications, and were studied in this work. It is commonly accepted that the increase of charge density within the electrodes leads to higher actuation performance of an EAP actuator. In this work, significant efforts have been put into exploring highly porous conductive materials for assembling EAP actuators with high specific surface area electrodes. The materials with highest potential for this purpose are highly porous amorphous carbons and carbide-derived carbons (CDC), commonly used in energy storage devices – supercapacitors. Promising less expensive alternatives are also carbon aerogels. In this thesis, carbide-derived carbon (CDC), coconut shell-based activated carbon, and carbon aerogel powders (activated and non-activated) were investigated as new alternative materials for application in electroactive polymer (EAP) actuator electrodes. The respective electrode materials were tested in five-layered actuator systems composed of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-TF)-impregnated Nafion membrane between two carbon electrode layers and gold foil on the surface. The electromechanical, electrochemical and mechanical characteristics of the prepared EAP actuators were examined and compared to the actuators based on RuO2 electrodes. The EAP actuator assembled with carbide-derived carbon electrodes produced the highest bending strain among the samples, up to 2.04% at ±2 V square-wave input, exceeding the strain of RuO2 electrodes by more than twice. The detailed analysis of the measured data indicates that the actuation performance of the EAPs is strongly affected by the porosity parameters and structural rigidity (degree of graphitization) of the carbon electrode materials. The effects of single-walled carbon nanotube (SWCNT) additives on the actuation performance were investigated in three-layered actuator systems composed of polymeric 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) electrolyte layer between two SWCNT/CDC electrode layers. The actuators were assembled with five different ratios of SWCNTs to CDC in the electrodes and their electromechanical, electrochemical and mechanical properties were comparatively analyzed. Analysis of the measured data demonstrates that the increase of the content of SWCNTs in the composite electrodes increased considerably the conductivity of electrodes and the stiffness (Young’s modulus) of the actuators. The addition of SWCNTs into the electrodes improved significantly the bending strain output. At low frequency range (5 mHz–0.5 Hz), the SWCNT/CDC (50/50)-actuator showed by far the highest bending strain among the tested samples (up to 0.85%), which compared to the pure CDC electrodes with maximum strain of 0.35% is an improvement of more than two times. A strong co-effect of the specific capacitance and Young’s modulus on the bending strain was observed at the lower frequency range.
Electroactive polymers (EAPs) are a type of smart materials that convert electrical pulse energy into mechanical deformation or vice versa, and hence, can be utilized as actuators or sensors. EAPs are promising functional materials for engineering new and increasingly demanded actuation systems that are silent, mechanically compliant, lightweight, structurally simple, and easily scalable. Ionic type of EAPs that consist of electrolyte containing membrane between two conductive electrode layers are especially attractive for bio-robotic applications, and were studied in this work. It is commonly accepted that the increase of charge density within the electrodes leads to higher actuation performance of an EAP actuator. In this work, significant efforts have been put into exploring highly porous conductive materials for assembling EAP actuators with high specific surface area electrodes. The materials with highest potential for this purpose are highly porous amorphous carbons and carbide-derived carbons (CDC), commonly used in energy storage devices – supercapacitors. Promising less expensive alternatives are also carbon aerogels. In this thesis, carbide-derived carbon (CDC), coconut shell-based activated carbon, and carbon aerogel powders (activated and non-activated) were investigated as new alternative materials for application in electroactive polymer (EAP) actuator electrodes. The respective electrode materials were tested in five-layered actuator systems composed of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-TF)-impregnated Nafion membrane between two carbon electrode layers and gold foil on the surface. The electromechanical, electrochemical and mechanical characteristics of the prepared EAP actuators were examined and compared to the actuators based on RuO2 electrodes. The EAP actuator assembled with carbide-derived carbon electrodes produced the highest bending strain among the samples, up to 2.04% at ±2 V square-wave input, exceeding the strain of RuO2 electrodes by more than twice. The detailed analysis of the measured data indicates that the actuation performance of the EAPs is strongly affected by the porosity parameters and structural rigidity (degree of graphitization) of the carbon electrode materials. The effects of single-walled carbon nanotube (SWCNT) additives on the actuation performance were investigated in three-layered actuator systems composed of polymeric 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) electrolyte layer between two SWCNT/CDC electrode layers. The actuators were assembled with five different ratios of SWCNTs to CDC in the electrodes and their electromechanical, electrochemical and mechanical properties were comparatively analyzed. Analysis of the measured data demonstrates that the increase of the content of SWCNTs in the composite electrodes increased considerably the conductivity of electrodes and the stiffness (Young’s modulus) of the actuators. The addition of SWCNTs into the electrodes improved significantly the bending strain output. At low frequency range (5 mHz–0.5 Hz), the SWCNT/CDC (50/50)-actuator showed by far the highest bending strain among the tested samples (up to 0.85%), which compared to the pure CDC electrodes with maximum strain of 0.35% is an improvement of more than two times. A strong co-effect of the specific capacitance and Young’s modulus on the bending strain was observed at the lower frequency range.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
ajamid, elektroaktiivsed polümeerid, nanopoorsed materjalid, süsinikmaterjalid, actuators, electroactive polymers, carbon materials, nanoporous materials