Assessment of the Wettability of Hydrophobic Solid Substrate by Biosurfactant Produced by Bacillus aryabhattai SPS1001.

Characterized biosurfactant produced by Bacillus aryabhattai SPS1001 isolated from crude oil contaminated soil of Haldia Oil Refinery, IOCL, West Bengal, India, was used to evaluate the surface energy and wettability of hydrophobic substrate by sessile drop method. Bacterial cell culture with cells removed was screened for biosurfactant production by drop collapse assay where drop diameter measured was 12.53 ± 0.01 mN/m and 11.79 ± 0.01 mN/m, respectively, on using hydrophobic substrate diesel oil and n-hexadecane in mineral salt medium. Moreover, the surface tension recorded was 24.4 ± 0.02 and 25.9 ± 0.02 mN/m, whereas interfacial tension measured was 0.28 ± 0.02 and 0.35 ± 0.04 mN/m against diesel oil and n-hexadecane, respectively. Additionally, at liquid-solid (silicone oil-coated glass surface) interface, decrease in contact angles of cell culture with cells removed sample (14.02 ± 0.2° and 14.95 ± 0.6°) translated into increase in surface energy of hydrophobic solid surface and quantitatively measured to 23.70 (diesel oil) and 24.57 (n-hexadecane) mN/m, respectively. Presence of biosurfactant in cell culture with cells removed sample plays an important role in lowering contact angle and in deciding the wetting condition of an oil-wet solid (silicone oil-coated) glass surface to water-wet state. Hence, the wetting property of biosurfactant finds applications in various areas such as coating, printing, etc.