Influence of dopant anions on the electrochemical properties of polypyrrole films
Date
2010-11-25
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Abstract
Elektrit juhtivad polümeerid on eriliste omadustea materjalide klass, mille populaarsus on kasvanud viimase paarikümne aasta jooksul – eelkõige tänu nende valmistamise lihtsusele ning perspektiivsetele tehnoloogilistele rakendustele. On hästi teada, et polümeerid (plastmassid) ei juhi elektrit. Avastus, et mõned polümeerid võivad olla pooljuht omadustega või isegi juhid (juhtivad omadused võrreldavad metallidega) oli algtõukeks uuele teadusvaldkonna aengule – juhtivate polümeeride uurimisele.
Nimetatud valdkonna avastamist ja arendamist on maailmas peetud niivõrd oluliseks, et 2000 aasta Nobeli preemia anti just juhtivate plümeeride uurijatele: Alan. J. Heegerile, Alan. G. MacDiarmid,ile ning Hideki Shirakawale polüatsetüleeni avastamise eest 1977 aastal.
Juhtivate polümeeride peamised köitvad eelised võrreldes teiste juhtivate materjalidega on nende potentsiaalne töötlemise lihtsus, suhteliselt hea mehaaniline vastupidavus, kõrge elektrijuhtivus, struktuuri paindlikkus, kergus ning praeguse hetkeni juba teadaolevad atraktiivsed ja huvitavd tehnoloogilised rakendused. Juhtivatest polümeeridest üks kõige lootustandvamaid on polüpürrool, tänu oma püsivale ning heale elektrijutivusele ning stabiilsusele võrreldes teiste juhtivate polümeeridega. Lisaks on polüpürrool osutunud bioühilduvaks, mistõttu on teda võimalik kasutada proteesides, kunstlihastes ning närvikudede sidumiseks.
Juhtivate polümeeride võimalikke rakendusi on palju ning nende arv pidevalt kasvab, kuna antud materjalide uurimine ning omaduste täiendamine jätkub. Juhtivaid polümeere on kasutatud väga erinevates valdkondades näiteks meditsiinis, sõjaväes, pooljuhttoodete tööstuses. Märkimisväärseid jõupingutusi on tehtud nende rakendamiseks sensorites, implantaatides, polümeersetes patareides, keemilistes vooluallikates. Veel on kasutatud juhtivaid polümeere korrosiooni kaitses, sõjaväes kaitseriietuste valmistamisel, antistaatiliste kattematerjalide valmistamisel ning ioone selekteerivate ja lahutavate membraanide valmistamisel jne.
Elektrokeemilise sünteesi käigus sisenevad polümeeri anioonid (dopandid), mis peale langu tasakaalustamise rolli omavad suurt mõju tekkiva polümeeri struktuurile ja sellega omakorda teistele omadustele.
Käesolevas töös uuriti detailselt kolme aromaatse-aniooni: benseensulfonaat-aniooniga (BS); para-tolueensulfonaat-aniooniga ja naftaleen-1,5-disulfonaat-aniooniga dopeeritud polüpürrooli (PPy) elektrokeemilisi omadusi vesilahustes. Erineva paksusega kilesid sünteesiti elektrokeemiliselt konstantsel voolutihedusel. Põhiliseks kasutatavaks uurimismeetodiks oli tsükliline voltamperomeetria. Täiendavat informatsiooni saadi mikroanalüüsist (EDS), kvantkeemilistest arvutustest ning pinnauuringutest aatomjõu mikroskoopia meetodiga (AFM.).
Eksperimentaalsed uuringud näitasid, et need võrdlemisi sarnaste dopantioonidega (benseensulfonaat vs para-tolueensulfonaat) sünteesitud kiled omavad üsna erinevaid elektrokeemilisi omadusi sõltuvalt lahuse koostisest ning paksusest. Elektrokeemilised mõõtmised näitasid, et aromaatsete dopantidega dopeeritud kilede redoksaktiivsust on võimalik oluliselt tõsta ümberdopeerimisega 2 korda ning suurim redoksaktiivsus saavutati kõikide kilede korral naatriumsulfaati sisaldavas lahuses. Kahjuks polümeeride korral ei realiseeru kogu laeng s.t kogu polümeer ei ole elektrokeemiliselt aktiivne. Ümberdopeerimise tulemused näitasid aga seda, et on võimalik saavutada olukord, kus kogu polümeer on elektrokeemiliselt aktiivne, mitõttu on antud kiled perspektiivsed kasutada keemilistes voolualliktes. Mõõtmistulemused näitasid, et dopeerimisastmed antud kilede korral olid suhteliselt kõrged (≈ 0.4) ületades kirjanduses väljapakutud tulemusi.
The essential results of the present electrocehmical study of polypyrrole films doped originally with aromatic anions such as BS; pTS and NDS and measured in various types of electrolytes can be listed as follows. • The comparative study of the properties of PPy films doped with three different aromatic sulfonate anions using four methods revealed that these similar-looking anions have quite different behavior as dopants. • It was established, that the process of reoxidation of the PPy film after reduction in solution containing the same anion as used in the electrodeposition solution is slow and the restoration of the initial redox charge needs additional polarization for more than 10 min. Due to the compact structure of PPy films doped with aromatic anions the mobility of anions and cations is restricted which causes irreversibility of redoxprocesses. • The voltammetric measurements show that redoxactivity (in solution containing the same anion as used in the electrodeposition solution) of the polypyrrole films doped with these sulfonate ions increases in the sequence pTS< BS< NDS, mostly due to the different mobility of cations. The mobility of the ions in these films is mainly determined how densely the films are packed, which in turn partly depends on the interactions between the dopant-anion and polymer chains. • The results of voltammetric measurements and XDS analyses show that ion exchange between PPy films and solution is relatively quick. It was established that small inorganic anions as NO3-, CI-, ClO4- can relatively easily replace aromatic sulfonates in PPy/BS and PPy/pTS films simply during 10 min polarization at 0.4 V. Only one potentiodynamic cycle needed for essential increase of the rate and fullness of the self-exchange of the anions. • The highest redoxactivity and doping levels in the case of all films orginally doped with aromatic anions were obtained in solution Na2SO4. The self- exchange ability of the double charged SO42- anion is more pronounced and the exchange process does not need electrochemical activation. • The redoxcapacity and corresponding electrochemical doping level of the redoped PPy films are essentially higher than that before ion exchange, showing that the PPy matrix formed in the presence of sulfonate anions does not collapse after ion exchange and it creates good conditions for the mobility of smaller inorganic anion. • The results of electrochemical measurements show clearly that the PPy films synthesized in the presence of BS, pTS and NDS and redoped by self-exchange with chloride, nitrate, perchlorate and sulfate anions have good redoxcapacity and stability.
The essential results of the present electrocehmical study of polypyrrole films doped originally with aromatic anions such as BS; pTS and NDS and measured in various types of electrolytes can be listed as follows. • The comparative study of the properties of PPy films doped with three different aromatic sulfonate anions using four methods revealed that these similar-looking anions have quite different behavior as dopants. • It was established, that the process of reoxidation of the PPy film after reduction in solution containing the same anion as used in the electrodeposition solution is slow and the restoration of the initial redox charge needs additional polarization for more than 10 min. Due to the compact structure of PPy films doped with aromatic anions the mobility of anions and cations is restricted which causes irreversibility of redoxprocesses. • The voltammetric measurements show that redoxactivity (in solution containing the same anion as used in the electrodeposition solution) of the polypyrrole films doped with these sulfonate ions increases in the sequence pTS< BS< NDS, mostly due to the different mobility of cations. The mobility of the ions in these films is mainly determined how densely the films are packed, which in turn partly depends on the interactions between the dopant-anion and polymer chains. • The results of voltammetric measurements and XDS analyses show that ion exchange between PPy films and solution is relatively quick. It was established that small inorganic anions as NO3-, CI-, ClO4- can relatively easily replace aromatic sulfonates in PPy/BS and PPy/pTS films simply during 10 min polarization at 0.4 V. Only one potentiodynamic cycle needed for essential increase of the rate and fullness of the self-exchange of the anions. • The highest redoxactivity and doping levels in the case of all films orginally doped with aromatic anions were obtained in solution Na2SO4. The self- exchange ability of the double charged SO42- anion is more pronounced and the exchange process does not need electrochemical activation. • The redoxcapacity and corresponding electrochemical doping level of the redoped PPy films are essentially higher than that before ion exchange, showing that the PPy matrix formed in the presence of sulfonate anions does not collapse after ion exchange and it creates good conditions for the mobility of smaller inorganic anion. • The results of electrochemical measurements show clearly that the PPy films synthesized in the presence of BS, pTS and NDS and redoped by self-exchange with chloride, nitrate, perchlorate and sulfate anions have good redoxcapacity and stability.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
dissertatsioonid, keemia, anioonid, polüpürrool, elektrokeemia