Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, corrosion means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Such type of damage typically produces oxide(s) and/or salt(s) of the original metal.
Corrosion resistant coatings protect metal components against degradation due moisture, salt spray, oxidation or exposure to a variety of environmental or industrial chemicals. A wide variety of corrosion resistant coating types are available to match the performance requirements of a specific application. Several other techniques to control or prevent corrosion are known such as anodization, cathodic protection, biofilm coatings and controlled permeability formwork.
The anti-corrosion coating of conjugated polymers is reported in the literature, where G. Kousik, in Progress in Organic Coatings 43 (2001) 286-291 describes in situ electro polymerization of polythiophene coating for providing corrosion protection to mild steel surface.
Further the conjugated polymers based on amino derivatives of poly(phenylene vinylene)s as corrosion protective coatings in marine environments is highlighted by ZARRAS Peter in PACE 2004, pp. 175-181 [Note(s): [226 p.][Document: 7 p.] whereas improved synthesis and corrosion properties of Poly(bis-(dialkylamino)phenylene vinylene)s (BAMPPV) is reported in Electroactive Polymers for Corrosion Control Chapter 8, pp 140-155 by Nicole Anderson et al.
Additionally U.S. Pat. No. 6,762,238 (Sze Cheng Yang et al.) discloses anti-corrosive coating composition which contains a polymeric complex useful as a water-borne paint to be applied onto a metal substrate electrophoretically or non-electrophoretically also European Patent No. EP19962441 discloses corrosion resistant coatings comprising electrically conductive polymer for biodegradable metallic stents; wherein an implantable stent comprising a biodegradable magnesium or magnesium alloy metallic region and a biodegradable polymeric corrosion resistant coating over the biodegradable metallic region that slows the rate of corrosion of the biodegradable metallic region upon implantation into a subject, wherein said corrosion resistant coating comprises an electrically wherein an imaging contrast agent, is gold particles.
Conjugated polymers (CPs) represent a major class of active materials in electronic devices. They have also become the material of choice for antistatic coating, buffer layers and protective coatings. CPs based protective coatings are proposed to impede metal and alloy (MA) oxidation by either acting as barrier coating or inducing metal alloy oxidation that results in formation of an oxide barrier layer. MA are prone to atmospheric oxidation by virtue of their higher Fermi energy level compared to the oxygen energy level (−5.2 eV with respect to vacuum). Because of the commensurate energy levels, the electron transfer from the MA to oxygen is facile and results in the formation of oxides of MA. The oxides do not possess the desirable properties of the native state of MA, hence the oxide formation is a disadvantage.
The conducting polymers and their applications is disclosed in, Current Physical Chemistry, 2012, 2, 224-240 (Murat Ates et al.) wherein conducting polymers such as poly(thiophene), poly(para-phenylene vinylene), poly(carbazole), polyaniline, polypyrrole, are useful in supercapacitors, Light emitting diodes (LEDs), Solar cells, Field effect transistor (FET), and Biosensors.
It also discloses the combination of poly(3-hexylthiophene) (P3HT) and ([6,6]-phenyl-C61-butyric acid methyl ester) PCBM (C60 derivative), which shows good photovoltaic properties with efficiencies beyond 5%.
Youngkyoo Kim et al. in Nature Materials 5, 197-203 (2006) discloses strong regioregularity effect in self-organizing conjugated polymer films and high-efficiency polythiophene: fullerene solar cells” the influence of polymer regioregularity (RR) on the molecular nanostructure, material properties and device performance, wherein the highest efficiencies have been achieved using blends of poly(3-hexylthiophene) (P3HT) and a fullerene derivative also supported by O. Ourida et al. in SATRESET, Vol. 1, No. 3, pp. 90-92, 2011. However Vanlaeke, Peter et al. in Solar Energy Materials and Solar Cells, 90(14). p. 2150-2158, 2006 describes the performance of organic solar cells based on the blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM).
Further Annick Anctil et al. in MRS Proceedings/Volume 1031/2007 reports composite blends of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinyl ene](MEH-PPV) and poly(3-hexylthiophene)—(P3HT with PCBM[60] and PCBM[70]. in the 1:4 MEH-PPV:PCBM ratio.
CPs that are used for MA oxidation prevention have a HOMO frontier orbital energy above the oxygen energy level, making the CPs susceptible for atmospheric oxidation (cf FIG. 1) upon oxidation, the holes generated on the polymer are filled by electrons transferred from the MA resulting in formation of an oxide layer. The electron transfer pathways of polymer coated MA have been shown in (FIG. 1).
Due to abundance of oxygen in the atmosphere, the spontaneous process of cascade electron transfer continues to oxidize the MA which leads to corrosion; also any cracks in the oxide layer would lead to delamination of the CPs and expose the substrate to an oxidation environment. Also the pores and the excitons on the polymer aggravate substrate oxidation, thus to increase the polymer's effectiveness in preventing metal oxidation, the pores in the polymer films must be blocked and the excitons must be quenched.
In view of above there is need to prevent the metal and alloy oxidation by employing the conjugated polymer having the electron energy (HOMO) level below oxygen energy level where the spaces of pinholes or pores of polymer surface is blocked by hydrophobic, spherical molecule to repel or preclude the oxidizing species from reaching the metal alloy.