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Nanoscale Electrical and Mechanical Characteristics of Conductive Polyaniline Network in Polymer Composite Films
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-4431-0671
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2014 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 6, no 21, 19168-19175 p.Article in journal (Refereed) Published
Abstract [en]

The presence and characteristics of a connected network of polyaniline (PANI) within a composite coating based on polyester acrylate (PEA) has been investigated. The bulk electrical conductivity of the composite was measured by impedance spectroscopy. It was found that the composite films containing PANI have an electrical conductivity level in the range of semiconductors (order of 10–3 S cm–1), which suggests the presence of a connected network of the conductive phase. The nanoscopic distribution of such a network within the cured film was characterized by PeakForce tunneling atomic force microscopy (AFM). This method simultaneously provides local information about surface topography and nanomechanical properties, together with electrical conductivity arising from conductive paths connecting the metallic substrate to the surface of the coating. The data demonstrates that a PEA-rich layer exists at the composite–air interface, which hinders the conductive phase to be fully detected at the surface layer. However, by exposing the internal structure of the composites using a microtome, a much higher population of a conductive network of PANI, with higher elastic modulus than the PEA matrix, was observed and characterized. Local current–voltage (IV) spectroscopy was utilized to investigate the conduction mechanism within the nanocomposite films, and revealed non-Ohmic characteristics of the conductive network.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014. Vol. 6, no 21, 19168-19175 p.
Keyword [en]
conducting polymer, polyaniline, conductive network, PeakForce TUNA AFM
National Category
Polymer Chemistry
URN: urn:nbn:se:kth:diva-155188DOI: 10.1021/am505161zISI: 000344978200098ScopusID: 2-s2.0-84910129848OAI: diva2:760086
Swedish Foundation for Strategic Research Swedish Research Council

QC 20141119. QC 20150112. Updated from e-pub ahead of print to published.

Available from: 2014-11-03 Created: 2014-11-03 Last updated: 2015-01-12Bibliographically approved
In thesis
1. Functional composite coatings containing conducting polymers
Open this publication in new window or tab >>Functional composite coatings containing conducting polymers
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic coatings are widely used to lower the corrosion rate of metallic structures. However, penetration of water, oxygen and corrosive ions through pores present in the coating results in corrosion initiation and propagation once these species reach the metal substrate. Considering the need for systems that offer active protection with self-healing functionality, composite coatings containing polyaniline (PANI) conducting polymer are proposed in this study. In the first phase of my work, PANI was synthesized by various methods and characterized. The rapid mixing synthesis method was chosen for the rest of this study, providing PANI with high electrical conductivity, molecular structure of emeraldine salt, and morphology of spherical nanoparticles. PANIs doped with phosphoric and methane sulfonic acid revealed hydrophilic nature, and I showed that by incorporating a long-chain alkylphosphonic acid a hydrophobic PANI could be prepared. The second phase of my project was dedicated to making homogenous dispersions of PANI in a UV-curable resin based on polyester acrylate (PEA). Interfacial energy studies revealed the highest affinity of PEA to PANI doped with phosphoric acid (PANI-PA), and no attractive or long-range repulsive forces were measured between the PANI-PA surfaces in PEA.This is ideal for making conductive composites as, along withno aggregation tendency, the PANI-PA particles might come close enough to form an electrically connected network. Highly stable PEA/PANI-PA dispersions were prepared by pretreatment of PANI-PA in acetone followed by mixing in PEA in small portions under pearl-milling. The third phase of my project dealt with kinetics of the free radical polymerization that was utilized to cure the PEA/PANI-PA mixture. UV-vis absorption studies suggested a maximum allowed PANI-PA content of around 4 wt.% in order not to affect the UV curing behavior in the UV-C region. Real-time FTIR spectroscopy studies, using a laboratory UV source, revealed longer initial retardation of the photocuring and lower rates of crosslinking reactions for dispersions containing PANI-PA of higher than 3 wt.%. The presence of PANI-PA also made the formulations more sensitive to changes in UV light intensity and oxygen inhibition during UV curing. Nevertheless, curing of the dispersions with high PANI-PA content, of up to 10 wt.%, was demonstrated to be possible at either low UV light intensities provided the oxygen replenishment into the system was prevented, or by increasing the UV light intensity to very high levels. In the last phase of my project, the PEA and PEA/PANI-PA coatings, cured under high intensity UV lamps, were characterized. SEM analysis showed small PANI-PA particles to be closely packed within the matrix, and the electrical conductivity of the composite films was measured to be in the range of semiconductors. This suggested the presence of a connected network of PANI-PA, as confirmed by investigations of mechanical and electrical variations at the nanoscale by PeakForce TUNA AFM. The data revealed the presence of a PEA-rich layer at the composite-air interface, and a much higher population of the conductive network within the polymer matrix. High current signal was correlated with a high elastic modulus, consistent with the level measured for PANI-PA, and current-voltage studies on the conductive network showed non-Ohmic characteristics. Finally, the long-term protective property of the coatings was characterized by OCP and impedance measurements. Short-term barrier-type corrosion protection provided by the insulating PEA coating was turned into a long-term and active protection by addition of as little as 1 wt.% PANI-PA. A large and stable ennoblement was induced by the coatings containing PANI-PA of up to 3 wt.%. Higher content of PANI-PA led to poorer protection, probably due to the hydrophilicity of PANI-PA facilitating water transport in the coating and the presence of potentially weaker spots in the film. An iron oxide layer was found to fully cover the metal surface beneath the coatings containing PANI-PA after final failure observed by electrochemical testing.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xviii, 85 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:42
Conducting polymer, Polyaniline, Conductive network, Nanocomposite, Active corrosion protection, Interfacial energy, UV curing
National Category
Polymer Technologies
Research subject
urn:nbn:se:kth:diva-155132 (URN)978-91-7595-301-4 (ISBN)
Public defence
2014-11-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20141103

Available from: 2014-11-03 Created: 2014-10-30 Last updated: 2016-02-02Bibliographically approved

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