In recent years, efficient, cost effective oil-water separation technologies are highly desired due to frequent oil spill accidents. To design fibrous membranes for efficient oil-water separation, 'flexible' polyamide acid (PAA), being polyamide acid with ether linkages in the backbone, and 'heavily' fluorinated polybenzoxazine (F-PB) were synthesized. Cellulose acetate (CA) and PM were co-axially electrospun; the PAA core was then imidizated at high temperature to obtain core/shell structured CA/polyimide (PI) electrospun fibrous membranes; subsequently the surface of the fibers was modified with F-PB, in the presence or in absence of silica nanoparticles (SNPs). The mechanical strength, surface wettability, chemical and thermal stability, and oil-water separation potential of thus obtained PI/CA fibrous membranes were evaluated. The membranes show a much higher critical tensile stress (130 MPa) and critical tensile strain (52%), when compared with CA fibrous membranes. Due to the use of the 'heavily' fluorinated polybenzoxazine, the membranes are superhydrophobic with a water contact angle of 162 degrees and an oil contact angle which approaches 0 degrees. Interestingly, the newly designed PI/CA/F-PB-1/SNP-4 membranes can effectively separate various oil-water mixtures, solely driven by gravity, with a high flux (3106.2 +/- 100 L m(-2) h(-1)) and a high separation efficiency (>99%) and thus possess great potential for oil-water separation. (C) 2016 Elsevier B.V. All rights reserved.