A separation device for use in separating a liquid-liquid mixture, and methods for preparing a separation device and using said separation device for separating a liquid-liquid mixture are disclosed. The separation device comprises a porous substrate and a coating formed on at least one surface of the porous substrate, wherein the coating comprises a plurality of polyelectrolyte layers of opposite charge formed on the at least one surface of the porous substrate in an alternating layer by layer electrostatic arrangement, and a plurality of nano-fibrillated species collectively formed as a capping layer electrostatically coupled to an outermost polyelectrolyte layer of said plurality of alternating polyelectrolyte layers.