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The effect of the polyaniline (PANI) layer thickness on impedance characteristics has been investigated. It has been found that PANI layer thickness has a significant influence on the impedance response of the PANI layer. The impedance response of PANI layers, presented in the low frequency region of Nyquist spectra, indicates an increase of real and imaginary impedance values as PANI layer thickness increases. Presentations of EIS data in Bode diagrams suggest two separate processes detected in the low and in the high frequency regions, respectively. The model used to analyze EIS data in terms of an electrical equivalent circuit resulted in PANI capacitance and PANI resistance values used, to calculate time constants for each of the processes. The EIS parameters, obtained from EIS data analysis, were used to interpret processes taking place inside PANI and at the PANI | electrolyte interface. The two major processes have been identified. The EIS analysis parameters are used to explain the changes of the PANI layer structure and of the PANI | electrolyte interface. In this work the total PANI layer capacitance, calculated from PANI EIS parameters, was compared to PANI current obtained by scanning the layer in the supporting electrolyte. The total PANI layer capacitance, in the potential region where the conductive form of PANI is present, was calculated as a function of two capacitances in series.

The aim of this work was to study protecting properties of PANI layers of different degrees of protonation in 0.1 mol dm-3 NaCl solution. Methods of testing, used in this work, were open circuit potential monitoring and Electrochemical impedance spectroscopy. Different degrees of PANI protonation were obtained by keeping the layer during one day in different solutions, like 3 mol dm-3 phosphoric acid solution (pH=0.4), or in buffer solutions (pH=4.3, pH=7.8). Although all the layers were tested in the same solution, depending on a degree of previously achieved protonation, different protecting properties were obtained. The best protecting properties, in solution containing Cl-, were obtained with the polymer layer kept before testing during one day in buffer solution of pH=7.8 where a complete deprotonation was achieved. It points out that PANI presents physical barrier to the ingress of chloride ions to the passive film and no additional electrochemical mechanism is present.

In this work the influence of ortho-phenylenediamine (OPDA) addition in the process of aniline polymerisation has been examined. The electrochemical polymerisation of the layer was carried out by means of cyclic voltammetry. The study of PANI layer characteristics were carried out on two substrates: Pt- and stainless steel electrode. The investigations on Pt-electrode were carried out for the layer obtained from 0.1M aniline with the addition of 1 and 5 mM of OPDA, all in 3 M phosphoric acid solution. The characteristics of the obtained layer were investigated by examining the catalytic effect of the different layers on H2Q/Q test redox system by means of RDE voltammetry. It was found that there is present a catalytic effect on the potential of H2Q/Q redox reaction, but the resulting limiting current decreases as the addition of OPDA increases, indicating that lower density of active centres, necessary for the catalytic oxidation, is available. The investigations on steel electrode (13% Cr) were carried out on a layer resulting from the polymerisation of 0.5M aniline with the addition of 5, 10 and 50 mM of OPDA. The layer was tested in Cl- solution by monitoring the open circuit potential (OCP). It was shown that, with the increase of OPDA addition, the time at OPC is prolonged. The AFM micrographs show the difference in morphology when OPDA is added, suggesting that OPDA additions cause the increased compactness of the polymer layer.

Poli(orto-etoksianilin)(POEA) je vodljivi polimer, derivat polianilina, koji kao i polianilin egzistira u tri osnovna oksidacijska oblika (LE-leukoemeraldin, EM-emeraldin i PG-pernigranilin) od kojih je najstabilniji emeraldinski oblik. Jedna od primjena polianilina je upotreba kod zaštite metala od korozije. Publiciran je niz radova [1, 2] u kojima je polianilin sintetiziran na površini mekog ili nerđajućeg čelika. Pokazalo se da poli(orto-etoksianilin) pruža dobru zaštitu čeliku od procesa korozije [3]. Upravo zbog toga u ovom radu je proučavana sinteza poli(orto-etoksianilna) na uzorku nerđajućeg čelika iz sumporno i fosforno kisele otopine. Sinteza je provođena iz 0, 5 moldm-3 orto-etoksianilina u 1, 5 mol dm-3 H2SO4 ili 3 mol dm-3 H3PO4 u granicama potencijala od – 400 mV do 1200 mV uz n=50 mV s-1. Za usporedbu sinteza je provođena i na Pt elektrodi uz iste uvjete sinteze, ali uz početni potencijala – 200 mV. Utvrđeno je da je sinteza POEA u fosfornoj kiselini sporija u odnosu na sintezu u sumpornoj kiselini. Također je utvrđeno da je sinteza znatno sporija na podlozi od nerđajućeg čelika u odnosu na Pt. Brzina rasta sloja je računata kao promjena količine naboja ispod strujnog vrha A (QA) u ovisnosti o broju ciklusa sinteze (N). Utvrđena su tri područja formiranja sloja (područje I, područje II i područje III). Područje I odgovara nukleaciji polimernog sloja i tu je uočena najveća razlika u brzini rasta na Pt i na nerđajućem čeliku. Usporeni početni rast pripisuje se otežanom stvaranju nukleusa POEA na uzorku nerđajućeg čelika i to, vjerojatno, zbog prisutnosti oksida. Područje II je područje rasta polimera na već formiranom sloju, gdje su brzine rasta na Pt i nerđajućem čeliku sličnije. Slično ponašanje je dobiveno kad je ispitivan polianilin [1]. U slučaju POEA u području III, kako na Pt tako i na čeliku, brzina rasta se ponovno usporava. Može se zaključiti da je broj centara preko kojih raste polimerni sloj smanjen. Ovakvo ponašanje nije uočeno kod polianilinskih slojeva [1]. Naglo usporenje rasta s vremenom u području III onemogućava nam sintezu debljih slojeva POEA što je bilo moguće u slučaju polianilina.

Provedena je elektrokemijska polimerizacija smjese anilin i orto-fenilendiamin monomera (OPDA) u otopini 1 moldm-3 solne kiseline na Pt- elektrodi. Ukupna koncentracija monomera (anilin +OPDA) iznosila je 0, 1 moldm-3. Sinteza je provođena cikličkom voltametrijom za otopine anilina uz udjele OPDA 5, 10, 50, 70 mmoldm-3 i čistog OPDA (tj. 0.1 mmoldm-3). Ustanovljeno je da se postizavanje iste debljine polimernog sloja usporava s porastom udjela OPDA. Karakterizacija polimernog sloja provedena je snimanjem sloja optičkim mikroskopom i Atomic Force mikroskopom (AFM). Ustanovljeno je da se već uz niske udjele OPDA mijenja morfologija polimernog sloja u odnosu na sloj čistog polianilina. Kod viših udjela OPDA (50 i 70 mmoldm-3), ustanovljeno je da se formiraju odvojena područja sloja koji se razlikuju po boji i morfologiji. Predložen je mehanizam rasta polimernog sloja koji uključuje, uz mogući kopolimer, i izdvojeni rast polianilina i poli(orto-fenilendiamina). Mehanizam polimerizacije koja rezultira poli(orto-fenilendiaminom) pretpostavlja se da uključuje "ljestvičastu" strukturu rasta polimernog lanca uz stvaranje fenazinskih prstenove.

The aim of this work was to study the protective properties of polyaniline (PANI) layers of different degrees of protonation on stainless steel immersed in c = 0.1 mol dm–3 NaCl solution. Methods of testing were open circuit potential monitoring, and electrochemical impedance spectroscopy. Different degrees of PANI protonation were obtained by keeping stainless steel covered with PANI layer during one day time in solutions of different pH values. The testing solutions were c = 3 mol dm–3 phosphoric acid solution (pH 0.4), and buffer solutions of pH 4.3 and pH 7.8. Although all PANI layers were tested in the same solution of c = 0.1 mol dm–3 NaCl, depending on a degree of previously achieved protonation, different protection time of steel samples was obtained. The best protective properties were obtained for steel covered with the PANI layer kept one day in the buffer solution of pH 7.8, before testing, where a complete deprotonation was achieved. The results obtained point out that PANI, under those conditions, presents a physical barrier to the ingress of chloride ions into the passive film, and the electrochemical mechanism of protection is not significantly involved.