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Ind. Eng. Chem. Res. 2010, 49, 2200–2205
Sonochemical Synthesis of ZnO Encapsulated Functional Nanolatex and its Anticorrosive Performance Shirish H. Sonawane,† Boon M. Teo,‡ Adam Brotchie,‡ Franz Grieser,‡ and Muthupandian Ashokkumar*,‡ Chemical Engineering Department, Vishwakarma Institute of Technology, Pune, India, and Particulate Fluids Processing Centre, School of Chemistry, UniVersity of Melbourne, Victoria 3010, Australia
ZnO/poly(butyl methacrylate) (PBMA) and ZnO-PBMA/polyaniline (PANI) nanolatex composite particles of 50 nm were synthesized by a hydrothermal-sonochemical emulsion polymerization technique. The anticorrosive performance of the synthesized latex was evaluated on a steel substrate. The anticorrosive performance was compared for acid/salt/alkali induced corrosion. It was found that the performance of the ZnO-PBMA coating for acid corrosion was superior to that of the ZnO-PBMA-PANI matrix. 1. Introduction The corrosion of metals is one of the most serious problems in the chemical and manufacturing industries. Generally, three approaches are used for corrosion inhibition: (i) cathodic protection, (ii) anodic protection, and (iii) barrier protection. In barrier protective coatings (e.g., paints), metal oxides/clay/ exfoliated particles are generally used as functional additives, in which they act as a barrier for moisture or oxygen transportation pathways.1,2 The application of water based polymer coatings containing metal oxides on metal surfaces is an interesting approach for providing a dense barrier against corrosion. The protection effectiveness of a coating also depends on the adhesion properties of the polymer on the metal surface. The barrier properties are also governed by the coating permeability of the corrosive species, which is an intrinsic property of the polymer coatings.2-4 The adhesive properties of poly(butyl methacryalate) (PBMA) are better than those of other methacrylate polymers. It is amorphous and less crystalline compared to poly(methyl methacryalate) (PMMA). In polymer surface coatings, a number of inorganic additives are added to improve the mechanical/physical/chemical properties of the film. For example, to improve the anticorrosive coating performance, chromium compounds have been widely used in surface coatings for large scale production. However, due to the highly toxic nature of chromium compounds, the development of effective chromium-free organic coatings is currently in progress. Kalendova and Vesely5 evaluated the anticorrosive performance of core shell zinc oxide, wollastonite, in organic coatings. Yeh and Chang6 found that the anticorrosive performance of polymer/layered silicate (PLS) is strongly influenced by their nanoscale layered structure and interfacial characteristics. Yeh et al.7-11 have also studied the anticorrosion performance of a number of nanocomposites that include polyaniline (PANI)-montmorillonite (MMT) MNT clay, poly(methyl methacrylate) (PMMA)/layered montmorillonite (MMT) clay, poly(o-methoxyaniline) (PMA)/Na+-montmorillonite (MMT) clay nanocomposite (Na+-PCN/PMMA), and PMMAsilica particles. Oxide semiconductor particles have also been used in coatings to reduce the transport of corrosion producing ions and to protect * To whom correspondence should be addressed. Tel.: +61-383447090. E-mail:
[email protected]. † Vishwakarma Institute of Technology. ‡ University of Melbourne.
the coating from photodegradation due to their inherent ability to absorb UV light.12 Chang et al.11 used amino-modified silica nanoparticles for corrosion protection of epoxy resin-silica hybrid materials. They found a better dispersion capability of modified nanoparticles in hybrid materials leading to an enhanced molecular barrier property, surface hydrophobicity, and anticorrosion performance. Zinc oxide exhibits anticorrosion capacity by accepting electrons from the metal.5 Due to this ability, nano ZnO can be used in anticorrosive coatings to prevent the corrosion reactions at the metal-coating interface. Metal oxides, especially zinc oxide13 and iron oxide,14 have been used as anticorrosion pigments in alkyd resin coatings. In these studies, the nanoadditives were mechanically dispersed into the alkyd resin along with a cross-linking agent. The addition of nanosize particles during the dispersion process, however, also leads to the aggregation of the particles, which is a major problem during the coating process. Furthermore, the lack of functionalization of the ZnO and its attachment to the polymer binder results in a poor performance of the coating. The sonochemical synthesis of polymer latex particles encapsulating presynthesized functional oxide particles has been recently studied. Teo et al.15 synthesized magnetite encapsulated poly(butyl methacrylate) latex particles by ultrasound assisted miniemulsion polymerization, with excellent colloidal stability and magnetic properties. The nanocomposite, synthesized using a water based miniemulsion process, is endowed with certain advantages, such as being formed via an environmentally friendly synthesis process, that yields a uniform distribution of oxides within the polymer matrix, and fast polymerization rates.
Figure 1. Extent of monomer conversion as function of sonication time for PBMA alone, PBMA-ZnO, and PBMA-ZnO-PANI.
10.1021/ie9015039 2010 American Chemical Society Published on Web 01/19/2010
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Figure 2. (A) Cryo-TEM image of nano PBMA-ZnO latex particles synthesized using sonochemical emulsion polymerization (100000× magnification). (B) TEM image of a ZnO nanoparticle synthesized using ultrasound assisted hydrothermal technique.
In this, and other studies, ultrasound has been used to initiate the polymerization process without the addition of an initiator.15-17 The latex particles formed are typically smaller than those formed in a conventional emulsion polymerization. This leads to an improvement in coverage area using a small quantity of latex for coating.18-20 In this paper, we report on the synthesis of functionalized ZnO and the incorporation of these particles into sonochemically synthesized polymer latex. The objectives of the present study are to (i) synthesize functionalized ZnO nanoparticles using sonochemistry, (ii) synthesize water based PBMA-ZnO latex nanoparticles using sonochemical emulsion polymerization, and (iii) evaluate the performance of ZnO-PBMA latex as an anticorrosive composite on a steel plate. In this study, 50 nm latex particles were synthesized. Due to the smaller size, the barrier to O2 diffusion may be expected to improve. The PBMA latex was chosen due to its better adhesion to the substrate. The addition of PANI was carried out to improve the transport of ions though the coating as PBMA is nonconductive. The ZnO was added into the latex as an anticorrosive pigment. The choice of the ZnO-PANI-PBMA system was to improve the corrosion resistance by both barrier and electrochemical mechanisms. 2. Experimental Details 2.1. Chemicals. Butyl methacrylate (BMA, 99%) was supplied by Aldrich, Australia. This monomer was filtered twice through aluminum oxide powder to remove the inhibitor, hydroquinone. The purified monomer was sealed and stored below 4 °C until further use. High purity (99%) sodium dodecyl sulfate (SDS) was purchased from BDH, Australia. PANI was purchased from Sigma-Aldrich (Mw ∼ 10,000 Da). Milli-Q filtered water was used to prepare all aqueous solutions. High purity argon, supplied by BOC Gases, was used for sparging solutions to eliminate oxygen from the solution. Zinc nitrate, sodium hydroxide, ammonium hydroxide solution, and SPAN 60 were procured from BDH, Australia, and were of research grade. 2.2. Synthesis of ZnO Nanoparticles Using the Sonochemical Technique. Zinc oxide was synthesized by reacting aqueous solutions of zinc nitrate and NaOH in the presence of an ultrasound probe operating at 20 kHz (Branson 450, Sonotrode 19 mm tip). Dilute solutions of Zn(NO3)2 (0.05 M,
250 mL) and sodium hydroxide (0.5 M, 150 mL) were prepared. Zinc nitrate solution was added into the ultrasound reactor followed by 10 mL of SPAN 60 (0.01 M). Dropwise addition of sodium hydroxide was carried out during the reaction. A white precipitate was formed after the addition of sodium hydroxide solution. The sonication was continued for 1 h to ensure completion of the reaction. Following sonication, the precipitate was removed, washed with ethanol and water several times, and dried. 2.3. Synthesis of Modified ZnO (Hydrophobic) for Latex Nanocomposite Synthesis. ZnO nanoparticles (2 g) were mixed with ethanol (50 mL) and then treated with myristic acid (0.02 g). The mixture was dispersed in an ultrasonic bath and then heated to 60 °C. Unreacted myristic acid was removed by ethanol washing, and the solid was dried prior to use. Polyaniline (PANI) (0.2 g) was modified using dodecylbenzenesulfonic acid (DBSA) (0.002 g) and HCl (0.30 mL) in ethanol and then dried. A 0.005 g sample of treated PANI was mixed with 1 mL of BMA and then added to the ultrasound reactor in order to prevent phase separation. 2.4. Miniemulsion Polymerization for ZnO-PBMA Nanolatex Synthesis. For the polymerization reaction, butyl methacrylate (8.175 g) and modified ZnO (0.1 g) were initially mixed thoroughly. Water (69 g) containing SDS (0.54 g) was thoroughly deaerated by bubbling with argon for 45 min at room temperature. Argon gas was passed over the surface of the liquid mixture to avoid air dissolving into the solution during the polymerization reaction. The liquid mixture was then subjected to sonication (20 kHz), which generated a uniform emulsion within 15 s. The sonochemical polymerization reaction was completed in less than 40 min. Cooling water was circulated around the reactor to maintain a constant reactor temperature at 20 °C. Samples were withdrawn at regular intervals to monitor the percentage conversion by gravimetric analysis.21 The conversion percentage is calculated using the mass of polymer and monomer as shown in eq 1: XA )
R1 - R2 × 100 M
(1)
where XA denotes conversion percentage of the monomer, R1 denotes the mass of composite particles (dry basis), R2 denotes the mass of nano ZnO, and M denotes the mass of the monomer.
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is the density of the metallic species in g/cm3. The weight loss was measured after carefully washing the samples with distilled water until the deposited corrosion product was removed, and finally, moisture was removed from the samples by oven drying at 60 °C. The thickness of coating was 50 µm. 2.6. Electrochemical Measurements. The electrochemical measurements were carried out using a standard three electrode assembly consisting of a working electrode (ZnO-PBMA latex), an Ag/AgCl reference electrode, and a platinum counter electrode. Other accessories used for electrochemical experiment included a potentiostat (MacLab). The voltammograms were measured between +1 and -1 V (vs Ag/AgCl) at a scan rate of 50 mV/s. The Tafel plots were recorded at a scan rate of 2 mV/s. Five samples were analyzed for corrosion rate in each solution, and an average reading was taken. Both electrochemical measurements and corrosion tests were performed at 25 °C.
Figure 3. Thermogravimetric analysis data for ZnO-PBMA latex.
2.5. Property Testing and Characterization of Latex Nanocomposite and Coatings. The polymer/ZnO nanocomposite samples were analyzed using a transmission electron microscope (TEM, CM10 Phillips). TEM samples were prepared by placing diluted drops of the samples on carbon coated grids and then drying. Thermogravimetric analysis was carried out using a Shimadzu TGA-51 from 100 to 500 °C with a step size of 2 °C. A steel strip of 40 × 25 × 2 mm was used for corrosion testing. The tests were conducted in acid, alkali, and salt solutions (HCl, NaOH, NaCl; 3.5 wt % each) by placing the uncoated and coated steel strips in beakers containing the appropriate solutions. The protective behavior of the coatings against corrosion was evaluated by calculating the corrosion rate (Rc) for each one of the samples by using eq 2:20,21 Rc )
∆Wl Atd
(2)
where ∆Wl is the weight loss in grams, A is the exposed area of the sample in cm2, t is the time of exposure in years, and d
3. Results and Discussion 3.1. Monomer Conversion in the Absence and Presence of ZnO. Figure 1 shows the conversion percentage of the monomer into polymer latex for PBMA, PBMA-ZnO, and PBMA-ZnO-PANI. For neat PBMA the conversion was found to be 77%, whereas in the presence of ZnO, the conversion was reduced slightly to 66%. A detailed mechanism of the sonochemical polymerization of methacrylate monomers has been described in previous publications.16 The presence of inorganic particles and organic solvents was found to decrease the rate of sonochemical polymerization.15,16 The latex particles embedded with ZnO are shown in a cryoTEM image (Figure 2A). It can be seen that the latex particles are densely packed with ZnO particles. The average particle size of ZnO nanoparticles is about 15 nm (Figure 2B). The latex particles are less than 50 nm in size. Figure 3 shows the thermogravimetric data of the PBMA-ZnO latex particles in the temperature range 100-500 °C. From 100 to 200 °C the major loss of the materials is due to oxidative pyrolysis of
Figure 4. Tafel plots of mild steel samples coated with different coatings in 3.5 wt % HCl solution.
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Table 1. Corrosion Parameters of Steel Samples Coated with Different Coatings in 3.5 wt % HCl Solution sample
Icorr (µA/cm2)
-Ecorr (V)
uncoated mild steel PBMA latex ZnO-PBMA latex ZnO-PBMA latex-PANI PBMA-PANI PANI
4.0 3.7 3.2 30 31 27
0.68 0.49 0.48 0.60 0.58 0.41
hydrocarbon moieties present in the polymer. A 50% loss in mass is found near 325 °C. This analysis demonstrates that water based ZnO-PBMA latex is thermally stable at high temperatures and hence is suitable for use in high temperature applications. 3.2. Electrochemical Characterization. Although the corrosion current (Icorr) cannot be measured directly, it can be estimated using a Tafel plot, such as that shown in Figure 4 for bare steel sample and the samples coated with ZnO-PBMA and PBMA latex in 3.5 wt % HCl. For these experiments, uncoated and coated steel strips were used as the working electrodes. In corrosion processes, as with any redox system, cathodic and anodic reactions occur simultaneously. The Tafel plot (E as a function of log(|I|), where I represents the total measured current, i.e., Ic + Ia) can isolate these two processes. Using the standard analysis method, the linear portions of curves are fitted, yielding the theoretical anodic and cathodic currents. The coordinates of the intersection of these fits are the corrosion current, Icorr and corrosion potential, Ecorr. These values are listed in Table 1 for the different coatings used. Based on this analysis, it was found that in HCl solution the sample without coating (bare sample) shows the maximum negative corrosion potential. The bare sample shows a corrosion potential of about -0.68 V, while PBMA and ZnO-PBMA coated samples have potentials of -0.49 and -0.48 V, respectively, as shown in Table 1. No difference in the corrosion potential is observed for the bare steel sample, PBMA coating, and ZnO-PBMA coating in NaCl solution. This indicates that the ZnO-PBMA coating does not show any anticorrosion effect in salt solution. It is also found that the open circuit potential shifts to a more cathodic region for the PBMA latex coating. The coating containing PBMA-ZnO gives a self-healing effect and shows a slight shift toward the cathodic region compared to the PBMA coating. With respect to the corrosion currents, as presented in Table 1, the lowest corrosion current density of 3.2 µA/cm2 is found for the sample coated with ZnO-PBMA. The highest corrosion current (31 µA) is observed for the PBMA-PANI coating (Figure 6). ZnO-PBMA-PANI shows a corrosion current density of 30 µA/cm2 (Figure 5), and the PANI coating shows a 12 µA/cm2 current density in HCl solution (Figure 7). This indicates that the coating containing PANI exhibits poor performance for corrosion inhibition. In salt solution, the corrosion current densities for the PANI and PBMA-PANI coatings were 43 and 38 µA/cm2, respectively. As shown in Figures 6 and 7, the PANI and PBMA-PANI coatings exhibit a lower current density in HCl solution compared to NaOH solution. Overall, the PBMA-PANI and PANI coatings show relatively higher currents in both HCl and NaOH (Figures 6 and 7). This might be due to the reaction of PANI with the electrolyte solution and thereby generating a higher current. Additionally, it was observed that the PANI coating did not adhere to the steel sample. The corrosion rates, surface coverages, and inhibition efficiencies for the bare sample and samples coated with PBMA,
Figure 5. Current as a function of potential for PANI-PBMA-ZnO latex in 3.5% HCl solution.
Figure 6. Current as a function of potential for PBMA-PANI nanocomposites for steel strips in NaCl and HCl solutions.
Figure 7. Current as a function of potential for PANI coating in NaCl and HCl solutions.
PBMA-ZnO, PBMA-ZnO-PANI, and PANI in three different solutions were monitored for a period of 200 h and are reported in Table 2. The visual observations are reported in Table 3 and in Figures 8 and 9. It was found that the PBMA-ZnO coating showed the lowest corrosion rate (0.20 mm/year) in comparison to the bare sample (0.62 mm/year). In HCl solution, PBMA-ZnO showed a 67% efficiency, which is the highest in comparison to the other coatings. In NaCl solution, the sample coated with PBMA-ZnO-PANI latex showed the lowest corrosion rate
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Figure 8. Photographs of steel strips dipped into HCl solution after 200 h of treatment.
Figure 9. Optical microscopic observations of PBMA-ZnO coating at different times in HCl solution: (a) 5 min, (b) 48 h, and (c) 200 h. Table 2. Corrosion Rate and Inhibition Efficiency Data for Different Coating Samples in 3.5 wt % Solution of NaOH, NaCl, and HCl coating used
surface coverage (mm2/g)
corrosion rate (mm/year)
inhibition efficiency, η (%)
bare MS MS with PBMA coating MS coated with PBMA-ZnO MS coated with PBMA-ZnO-PANI PANI bare MS MS with PBMA coating MS coated with PBMA-ZnO MS coated with PBMA-ZnO-PANI PANI bare MS MS with PBMA coating MS coated with PBMA-ZnO MS coated with PBMA-ZnO-PANI PANI
0.31 0.67 0.42 0.62 0.67 0.69 0.83 0.60 0.37 0.61 0.18 0.78
0.62 0.43 0.20 0.36 0.69 0.48 0.16 0.15 0.03 0.68 0.54 0.18 0.21 0.48 0.31
31.49 67.16 41.99 62.00 66.74 68.97 83.03 60.00 36.71 61.28 18.26 60.03
solution HCl 3.5 wt %
NaCl 3.5 wt %
NaOH 3.5 wt %
Table 3. Summary of the Performance of Coated Steel Panels in 3.5% HCl, 3.5% NaOH, and 3.5% NaCl Solutiona type of failure no.
coating system
1 2
bare MS MS with PBMA coating MS coated with PBMA-ZnO MS coated with PBMA-ZnO-PANI MS coated with PANI
3 4 5
3.5% HCl (for 200 h)
3.5% NaOH (for 200 h)
3.5% NaCl (for 200 h)
6 5,6
2 6
2 2
5
2
2
3,6
2,6
2
2,6
2
2,4,6
a No effect ) 1; whitening ) 2; shrinkage of film ) 3; blistering of film ) 4; removal of film ) 5; color change ) 6.
(0.03 mm/year) and the highest inhibition efficiency (83%). In the case of NaOH solution the PBMA coating showed the lowest corrosion rate (0.18 mm/year) while the inhibition efficiency for the PBMA-ZnO coating was found to be 61%. Collectively, the PBMA-ZnO coating showed a higher inhibition efficiency
in HCl solution, whereas the PBMA-ZnO-PANI coating showed a higher efficiency in NaCl solution. In NaOH solution, the PBMA-ZnO coating showed the higher inhibition efficiency. Color changes were observed prominently in the case of HCl solution for all the samples, as shown in Figure 8. It was seen that all the samples were red in color and, in the case of the ZnO-PBMA sample, some areas remained unaffected. The performance of the ZnO-PBMA coating was better in HCl solution due to the better dispersion of ZnO in the latex facilitating the formation of a well-adhered, dense, and continuous network-like structure, which retards the penetration of the corrosive ions through the metal substrate and inhibits the metal from attack by corrosive species.24-26 Hence, the PBMA-ZnO coating acts as an excellent inhibitor and protects metals from corrosion. 3.3. Possible Mechanism. Iron passivation occurs due to the presence of ZnO layer and the O2 barrier increases due to the thick polymer matrix. A possible mechanism is discussed below. The substrate donates an electron from Fe to the ZnO pinholes
Ind. Eng. Chem. Res., Vol. 49, No. 5, 2010
present in the coating. The transport of the electron occurs due to the presence of PANI in the coating. On the surface of the coating, Fe2+ is converted to Fe2O3 by combining with O2. Sathiyanarayanan et al.22 reported the plausible mechanism of corrosion inhibition in the presence of PANI-paint coating. Radhakrishnan et al.23 reported the mechanism for TiO2-PANI nanocomposite corrosion resistance coating. Some of the elementary steps of reactions reported are as follows: generation of electrons from the substrate: Fe f Fe2+ + 2e-
(R1)
generation of electrons from the iron substrate: Fe2+ f Fe3+ + e-
(R2)
neutralization at ZnO-PBMA coating: O2(g) + 2H2O + 4e- f 4OH-
(R3)
combination of electrons in pinholes of PBMA-ZnO coating: 2Fe2+(aq) + O2(g) + 2H2O f 2FeOOH + 2H+ (R4) Conclusions ZnO-PBMA and PANI-PBMA nanocomposite latexes were synthesized using a sonochemical emulsion polymerization technique. The corrosion performance of the coatings was evaluated in alkali, acid, and salt solutions. The corrosion rate of PBMA/ZnO was found to be lowest in HCl solution, with an inhibition efficiency of 67%. Additionally, the functionalized latex coatings were found be superior in performance to the normal latex coatings. Acknowledgment S.H.S. acknowledges the Department of Science and Technology (DST), Government of India, for providing the BOYSCAST Fellowship through Grant SR/BY/E-07/2008. The authors acknowledge Ken Goldie, Bio21 Institute, University of Melbourne for the cryo TEM work. Literature Cited (1) Soer, W.; Ming, W.; Koning, C.; Benthem, R.; Mol, J.; Terryn, H. Barrier and Adhesion Properties of Anti-corrosion Coatings Based on Surfactant-Free Latexes from Anhydride-Containing Polymers. Prog. Org. Coat. 2009, 65, 94. (2) Sangaj, N.; Malshe, V. Permeability of Polymers in Protective Organic Coatings. Prog. Org. Coat. 2004, 50, 28. (3) Phanasgaonkar, A.; Raja, V. Influence of Curing Temperature, Silica Nanoparticles and Cerium on Surface Morphology and Corrosion Behavior of Hybrid Silane Coatings on Mild Steel. Surf. Coat. Technol. 2009, 20, 2260. (4) Sauvant-Moynot, V.; Gonzalez, S.; Kittel, J. Self-healing Coatings: An Alternative Route for Anticorrosion Protection. Prog. Org. Coat. 2008, 63, 307. (5) Kalendova, A.; Vesely, D. Study of the Anticorrosive Efficiency of Zincite and Periclase-Based Core-Shell Pigments in Organic Coatings. Prog. Org. Coat. 2009, 4, 5. (6) Yeh, J.; Chang, K. Polymer/layered silicate nanocomposite anticorrosive coatings. Ind. Eng. Chem. 2008, 14 (3), 275.
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(7) Yeh, J.; Liou, S.; Lai, C.; Wu, P. Enhancement of Corrosion Protection Effect in Polyaniline via the Formation of Polyaniline-Clay Nanocomposite Materials. Chem. Mater. 2001, 13 (3), 1131. (8) Yeh, J.; Liou, S.; Lin, C.; Cheng, C.; Chang, Y. Anticorrosively Enhanced PMMA-Clay Nanocomposite Materials with Quaternary Alkylphosphonium Salt as an Intercalating Agent. Chem. Mater. 2002, 14 (1), 154. (9) Yeh, J.; Kuo, T.; Huang, H.; Chang, K.; Chang, M.; Yang, J. E. Preparation and characterization of poly(o-methoxyaniline)/Na+-MMT clay nanocomposite via emulsion polymerization: Electrochemical studies of corrosion protection. Eur. Polym. J. 2007, 43, 1624. (10) Yeh, J.; Weng, C.; Liao, W.; Mau, Y. Anticorrosively enhanced PMMA-SiO2 hybrid coatings prepared from the sol-gel approach with MSMA as the coupling agent. Surf. Coat. Technol. 2006, 201 (3-4), 1788. (11) Chang, K.; Lin, H.; Lin, C.; Kuo, T.; Huang, H.; Hsu, S.; Yeh, J.; Yang, J.; Yu, Y. Effect of Amino-Modified Silica Nanoparticles on the Corrosion Protection Properties of Epoxy Resin-Silica Hybrid Materials. J. Nanosci. Nanotechnol. 2008, 8 (6), 3040. (12) Chico, B.; Simancas, J.; Vega, J.; Granizo, N.; Diaz, I.; De la Fuente, D.; Morcillo, M. Anticorrosive Behaviour of Alkyd Paints Formulated with Ion-exchange Pigments. Prog. Org. Coat. 2008, 61, 283. (13) Dhoke, S.; Khanna, A.; Jai Mangal Sinha, T. Effect of Nano-ZnO Particles on the Corrosion Behavior of Alkyd-based Waterborne Coatings. Prog. Org. Coat. 2009, 64, 371. (14) Dhoke, S.; Khanna, A. Effect of Nano-Fe2O3 Particles on the Corrosion Behavior of Alkyd Based Waterborne Coatings. Corros. Sci. 2009, 51, 6. (15) Teo, B.; Chen, F.; Hatton, A.; Grieser, F.; Ashokkumar, M. Novel One-Pot Synthesis of Magnetite Latex Nanoparticles by Ultrasound Irradiation. Langmuir 2009, 25, 2593. (16) Teo, B.; Prescott, S.; Ashokkumar, M.; Grieser, F. Ultrasound Initiated Miniemulsion Polymerization of Methacrylate Monomers. Ultrason. Sonochem. 2008, 5, 89. (17) Ashokkumar, M.; Mason, T. Kirk-Othmer Encyclopedia of Chemical Technology; John Wiley & Sons: New York. (18) Teo, B.; Ashokkumar, M.; Grieser, F. Microemulsion Polymerizations via High-Frequency Ultrasound Irradiation. J. Phys. Chem. B 2008, 112, 5265. (19) Landfester, K. Polyreactions in Miniemulsions. Macromol. Rapid Commun. 2001, 22, 896. (20) Khaled, K.; Al Qahtani, M. The Inhibitive Effect of Some Tetrazole Derivatives Towards Al Corrosion in Acid Solution: Chemical, Electrochemical and Theoretical Studies. Mater. Chem. Phys. 2009, 113, 150. (21) Javed, A.; Ufana, R.; Ashraf, S.; Sharif, A. Corrosion-Protective Performance of Nano polyaniline/ferrite Dispersed Alkyd Coatings. J. Coat. Technol. Res. 2008, 5, 123. (22) Sathiyanarayanan, S.; Muthukrishnan, S.; Venkatachari, G.; Trivedi, D. Corrosion protection of steel by polyaniline (PANI) pigmented paint coating. Prog. Org. Coat. 2005, 53, 297. (23) Radhakrishnan, S.; Siju, C.; Mahanta, D.; Patil, S.; Madras, G. Conducting polyaniline-nano-TiO2composites for smart corrosion resistant coatings. Electrochim. Acta 2008, 54 (4), 1249. (24) Wei, Y.; Chang, P. Characteristics of Nano zinc oxide Synthesized Under Ultrasonic Condition. J. Phys. Chem. Solids 2008, 69, 688. (25) Wessling, B.; Schroder, S.; Gleeson, S.; Merkle, H.; Schroder, S.; Baron, F. Corrosion Prevention with an Organic Metal (polyaniline): Surface Ennobling, Passivation, Corrosion Test Results. Mater. Corros. 1996, 47, 439. (26) Schauer, A.; Joos, L.; Dulog, C.; Eisenbach, D. Protection of Iron against Corrosion with Polyaniline Primers. Prog. Org. Coat. 1998, 33, 20.
ReceiVed for reView September 24, 2009 ReVised manuscript receiVed December 13, 2009 Accepted December 24, 2009 IE9015039
