Sensitivity of coalescence separation of oil–water emulsions using stainless steel felt enabled by LBL self-assembly and CVD

Abstract

Commercial stainless steel felt was endowed with LBL self-assembly of dual size nano-SiO₂ particles to have a hierarchical micro/nano surface structure. The pore size of the felt was tailored at the same time by tuning the assembling cycles. Chemical vapor deposition (CVD) of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) at two concentration levels was applied to the roughened felt to render it both hydrophobic/superhydrophobic and oleophobic. The felt thus prepared was wettable by oil underwater, which allowed it to be effective as a coalescing material for separating 4 kinds of oil-in-water emulsions. The nanometer-thick POTS coating was durable for months. The coalescence separation efficiency was found to be dependent on both pore size and surface wettability of the felt in air. It was less sensitive to pore size change when the surface was more hydrophobic and oleophobic (amphiphobic). When the pore size was kept constant, more amphiphobic felt was less efficient for separation. When the surface turned superhydrophobic, the separation became better as the pore size was reduced. These findings provide new insights for designing better coalescence materials, especially when the effects of surface wettability and pore size are intermingled.