Antibacterial and Hydrophobic Graphite-siloxane Composite Coating towards Microbial Corrosion Resistant Application of Steel: Experimental and Theoretical Insight

The fabrication of hydrophobic graphite-siloxane composite coating on low carbon steel (LCS) substrate using electrophoretic deposition is reported. At a critical concentration (~ 20 wt. %) of methyl hydrogen polysiloxane (trade name KF-99), it achieved the highest hydrophobicity of the composite coating (Contact angle ~122º). The corrosion resistance of the hydrophobic composite coating is examined in 3.5 wt—% NaCl solution. The potentiodynamic curves demonstrate that the corrosion rate is drastically reduced to 79.3 % for graphite-siloxane composite coating (cured at 400 ºC) than bare LCS substrate. Both grain refinement due to heat treatment and increment in water contact angle significantly contribute to increased corrosion resistance.Additionally, it is observed that graphite–siloxane composite coating shows good antibacterial properties, which may enable the coating to combat microbial corrosion of metals. To support the experimental findings, we have studied the interactions of water molecules on low-carbon steel and the hybrid structure of LCS/graphite and tri-layer LCS/ graphite/siloxane using sophisticated Density Functional Theory simulations. The adsorption energy data reflect that water strongly interacts with LCS, but interactions become weak with LCS/graphite and hydrophobic for LCS/graphite/siloxane, supporting the experimental data. There is a reduced interaction between the O 2p orbital of H2O with LCS with the addition of graphite, which further shows a drastic reduction with siloxane. The low H2O adsorption energy and reduced charge transfer from H2O to LCS in the presence of graphite-siloxane composites can confirm this.