The lap shear strength of polypyrrole coatings formed on low carbon steel (similar to 23 MPa) is shown to be significantly higher (by similar to 60%) than that obtained using uncoated steel as the adherend. The lap shear (adhesion) strength of polypyrrole-coated steel varied with the pH of the monomer-electrolyte soution and the applied current. The low carbon steel-containing polypyrrole coatings formed at low pH (pH less than or equal to 2.4) have higher adhesion strength than those coated with polypyrrole at higher pH (pH greater than or equal to 6.0). However, poly(N-methyl pyrrole)-coated steel showed significantly lower adhesion strength. Increasing the applied current density decreased the adhesion strength. The surface free energies of polypyrrole coatings, similar to 49-53 mJ/m(2) are similar to that obtained for uncoated low carbon steel, similar to 53 mJ/m(2), indicating that polypyrrole will effectively wet low carbon steel. The extent of wetting of low carbon steel by the coatings was additionally confirmed by an interaction parameter, phi, of unity. (C) 2002 Wiley Periodicals, Inc. [References: 22]
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