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Functional composite coatings containing conducting polymers
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
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.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:42
Keyword [en]
Conducting polymer, Polyaniline, Conductive network, Nanocomposite, Active corrosion protection, Interfacial energy, UV curing
National Category
Polymer Technologies
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-155132ISBN: 978-91-7595-301-4 (print)OAI: oai:DiVA.org:kth-155132DiVA: diva2:759588
Public defence
2014-11-20, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20141103

Available from: 2014-11-03 Created: 2014-10-30 Last updated: 2016-02-02Bibliographically approved
List of papers
1. Toward Homogeneous Nanostructured Polyaniline/Resin Blends
Open this publication in new window or tab >>Toward Homogeneous Nanostructured Polyaniline/Resin Blends
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2011 (English)In: ACS APPLIED MATERIALS & INTERFACES, ISSN 1944-8244, Vol. 3, no 5, 1681-1691 p.Article in journal (Refereed) Published
Abstract [en]

The high interest in applications of conducting polymers, especially polyaniline (PANI), makes it important to overcome limitations for effective usage due to poor processability and solubility. One promising approach is to make blends of PANT in polymeric resins. However, in this approach other problems related to the difficulty of achieving a homogeneous PANI dispersion arise. The present article is focused on this general problem, and we discuss how the synthesis method, choice of dopant and solvent as well as interfacial energies influence the dispersibility. For this purpose, different synthesis methods and dopants have been employed to prepare nanostructures of polyaniline. Dynamic light scattering analysis of dispersions of the synthesized particles in several solvents was employed in order to understand how the choice of solvent affects PANT aggregation. Further information on this subject was achieved by scanning electron microscopy studies of PANT powders dried from various solutions. On the basis of these results, acetone was found to be a suitable dispersion medium for PANI. The polymer matrix used to make the blends in this work is a UV-curing solvent-free resin. Therefore, there is no low molecular weight liquid in the system to facilitate the mixing process and promote formation of homogeneous dispersions. Thus, a good compatibility of the components becomes crucial. For this reason, surface tension and contact angle measurements were utilized for characterizing the surface energy of the PANI particles and the polyester acrylate (PEA) resin, and also for calculating the interfacial energy between these two components that revealed good compatibility within the PANI/PEA blend. A novel technique, based on centrifugal sedimentation analysis, was employed in order to determine the PANT particle size in PEA resin, and high dispersion stability of the PANI/PEA blends was suggested by evaluation of the sedimentation data.

Keyword
conducting polymer, polyaniline, synthesis methods, particle size, interfacial energy, dispersion stability, LUMiSizer dispersion analyzer
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-34404 (URN)10.1021/am2002179 (DOI)000290843800042 ()2-s2.0-80053645678 (Scopus ID)
Note
QC 20110607Available from: 2011-06-07 Created: 2011-06-07 Last updated: 2014-11-03Bibliographically approved
2. Direct measurement of colloidal interactions between polyaniline surfaces in a uv-curable coating formulation: The effect of surface hydrophilicity/ hydrophobicity and resin composition
Open this publication in new window or tab >>Direct measurement of colloidal interactions between polyaniline surfaces in a uv-curable coating formulation: The effect of surface hydrophilicity/ hydrophobicity and resin composition
2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 4, 1045-1054 p.Article in journal (Refereed) Published
Abstract [en]

The interactions between polyaniline particles and polyaniline surfaces in polyester acrylate resin mixed with 1,6-hexanediol diacrylate monomer have been investigated using contact angle measurements and the atomic force microscopy colloidal probe technique. Polyaniline with different characteristics (hydrophilic and hydrophobic) were synthesized directly on spherical polystyrene particles of 10 μm in diameter. Surface forces were measured between core/shell structured polystyrene/polyaniline particles (and a pure polystyrene particle as reference) mounted on an atomic force microscope cantilever and a pressed pellet of either hydrophilic or hydrophobic polyaniline powders, in resins of various polymer:monomer ratios. A short-range purely repulsive interaction was observed between hydrophilic polyaniline (doped with phosphoric acid) surfaces in polyester acrylate resin. In contrast, interactions between hydrophobic polyaniline (doped with n-decyl phosphonic acid) were dominated by attractive forces, suggesting less compatibility and higher tendency for aggregation of these particles in liquid polyester acrylate compared to hydrophilic polyaniline. Both observations are in agreement with the conclusions from the interfacial energy studies performed by contact angle measurements.

Keyword
1, 6-hexanediol diacrylate, Atomic force microscope cantilevers, Colloidal interaction, Colloidal probe techniques, Hydrophilic and hydrophobic, Polystyrene particle, Repulsive interactions, Surface hydrophilicity
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-142808 (URN)10.1021/la4035062 (DOI)000331015600011 ()2-s2.0-84893632402 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20140313

Available from: 2014-03-13 Created: 2014-03-12 Last updated: 2017-12-05Bibliographically approved
3. UV-curable acrylate-based nanocomposites: Effect of polyaniline additives on the curing performance
Open this publication in new window or tab >>UV-curable acrylate-based nanocomposites: Effect of polyaniline additives on the curing performance
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2013 (English)In: Polymers for Advanced Technologies, ISSN 1042-7147, E-ISSN 1099-1581, Vol. 24, no 7, 668-678 p.Article in journal (Refereed) Published
Abstract [en]

Composites of nanostructured polyaniline (PANI) conducting polymer in a polyester acrylate (PEA) formulation were made to provide conductive organic coatings. The effect of the presence and amount of PANI on the photocuring performance of the ultraviolet (UV)-curable acrylate system has been investigated employing real-time Fourier transform infrared spectroscopy as the main technique. Longer initial retardation of the radical polymerization and lower rates of cross-linking reactions were observed for dispersions containing PANI of higher than 3wt.%. The PEA/PANI samples were more affected than the neat PEA resin by the changes in UV light intensity and oxygen accessibility during UV curing. Samples with higher PANI content, of up to 10wt.%, were tested and could be partially cured even at UV light intensities as low as 2mW cm-2 when the oxygen replenishment into the system was inhibited. Thermal analysis revealed that the presence of PANI did not induce any significant change in Tg of the cured system, meaning that early decrease in mobility and vitrification is not the reason for lower ultimate conversion of the dispersions with higher PANI content compared with the neat PEA resin. Curing under strong UV lamps, of 1.5W cm-2 intensity, made it possible to reach high degrees of conversion on films with similar mechanical properties independent of the PANI content.

Keyword
Polyaniline, Polyester acrylate, Real-time FTIR spectroscopy, UV curing kinetics
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-134167 (URN)10.1002/pat.3131 (DOI)000320557400009 ()2-s2.0-84879404163 (Scopus ID)
Funder
Swedish Foundation for Strategic Research
Note

QC 20131120

Available from: 2013-11-20 Created: 2013-11-18 Last updated: 2017-12-06Bibliographically approved
4. Nanoscale Electrical and Mechanical Characteristics of Conductive Polyaniline Network in Polymer Composite Films
Open this publication in new window or tab >>Nanoscale Electrical and Mechanical Characteristics of Conductive Polyaniline Network in Polymer Composite Films
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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
Keyword
conducting polymer, polyaniline, conductive network, PeakForce TUNA AFM
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-155188 (URN)10.1021/am505161z (DOI)000344978200098 ()2-s2.0-84910129848 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

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

Available from: 2014-11-03 Created: 2014-11-03 Last updated: 2017-12-05Bibliographically approved
5. Active corrosion protection by conductive composites of polyaniline in a UV-cured polyester acrylate coating
Open this publication in new window or tab >>Active corrosion protection by conductive composites of polyaniline in a UV-cured polyester acrylate coating
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2016 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 90, 154-162 p.Article in journal (Refereed) Published
Abstract [en]

Polyaniline doped with phosphoric acid (PANI-PA) was synthesized and characterized by impedance and Raman spectroscopy. Exposure to UV-light resulted in a slight decrease in the PANI's electrical conductivity and no significant change in the oxidation state (of an emeraldine salt). Composite coatings containing 0, 1, 3 and 5 wt.% PANI-PA in a UV-curable polyester acrylate (PEA) resin were prepared and applied on polished carbon steel. Closely packed PANI-PA particles of several tens of nanometers were observed inside the composite coating by scanning electron microscopy, and a connected conductive network across the film was detected by Peak Force TUNA atomic force-microscopy. The evolution of open circuit potential and impedance data during long-term exposure to 3 wt.% NaCI electrolyte revealed that the short-term barrier-type corrosion protection provided by the insulating PEA coating can be turned into a long-term and active protection by addition of as little as 1 wt.% PANI-PA to the formulation. Stable ennoblement in the corrosive media was observed for the coatings containing conducting polymer up to 3 wt.%. However, higher content of PANI-PA (5 wt.%) led to poorer protective properties, 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
Elsevier, 2016
Keyword
Conductive composite coating, Polyaniline, Active corrosion protection, Electrochemical impedance spectroscopy
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-180980 (URN)10.1016/j.porgcoat.2015.10.008 (DOI)000367108200016 ()2-s2.0-84951816437 (Scopus ID)
Note

Updated from Manuscript to Article.

QC 20160128

Available from: 2016-01-28 Created: 2016-01-26 Last updated: 2017-11-30Bibliographically approved

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