Experimental Study of the Salinity-Specific Adhesion Force between Oil Drop and Underwater Superoleophobic Polyelectrolyte Surfaces

Creating surfaces with controlled superoleophobicity is of real significance for the manipulation, transportation, and self-cleaning of organic fluids of strategic importance. In the present work, particular attention is given to elucidate the superoleophobicity mechanism of surfaces coated with polyelectrolyte multilayers (PEMs) assembled by layer-by-layer deposition of the cationic polyelectrolyte polydiallyldimethylammonium chloride (PDDA) and the anionic polyelectrolyte poly(styrenesulfonate) (PSS) in 1.0 M NaCl solution. The atomic force microscopy (AFM) drop probe technique was used to measure the salinity-specific adhesion forces between the oil droplet and underwater polyelectrolyte PEM-coated surface. Meanwhile, topographic images of the fabricated PEMs in solutions with different ionic strengths were also obtained and compared. The results show that the fabricated (PDDA/ PSS)(1.5), (PDDA/PSS)(3.5), and (PDDA/PSS)(4.0) PEMs exhibit excellent oil repellency upon immersion into aqueous solutions with high salinity. Additionally, the underwater superoleophobicity of the prepared PEM films was well-demonstrated through AFM adhesion force measurements. It is proven in our study that the underwater superoleophobicity of the fabricated surface has a strong relationship with the salinity-specific behavior of deposited polyelectrolytes.