Superhydrophobic membrane with hierarchically 3D-microtexture to treat saline water by deploying membrane distillation

Preparation of membrane with lotus leaf-like surface is extremely important in direct contact membrane distillation (MD), to restrict invasion of the liquid into the membrane pores and consequently reducing membrane wettability. In this work, superhydrophobic membrane with an extreme water repellent surface has been designed by integrating 3D-hierarchical micro-textures on the membrane surface by using 5000 mesh fabric and non-woven as the templated substrates respectively. As shown in FESEM surface micrographs, different rough micro-scaled structures were thinly and uniformly distributed on the poly(vinylidene fluoride) (PVDF) membrane, fabricated in either water or ethanol coagulation bath. Membrane produced using non-woven templated deposition and immersed in ethanol coagulation bath has produced rough surface with an average static water contact angle of 156° and dynamic sliding angle of 5°. Meanwhile, 5000 mesh fabric template has generated microscopic-architecture on the membrane surface with static water contact angle of 157° and dynamic sliding angle of 8°. Surface roughness analyses illustrates relatively narrower and deeper micro-valley created on the membrane surface deposition on the non-woven templated substrate than that of 5000 mesh fabric template. The hierarchically 3D-microtexture membrane displayed good wetting resistance in MD separation by achieving high permeate flux up to 24 kg/m².h with salt rejection beyond 99.97 %. This study has qualitatively explain the contributions of the membrane surface roughness (micro- and nano-structures where tiny air pockets were trapped) towards its dynamic wetting behavior (sliding angle of water droplet slides from the membrane surface).