Xuewu Huang

Super-hydrophobic coatings based on non-solvent induced phase separation during electro-spraying

HYPOTHESIS The polymer solution concentration determines whether electrospinning or electro-spraying occurs, while the addition of the non-solvent into the polymer solution strongly influences the surface morphology of the obtained products. Both smooth and porous surfaces of the electro-sprayed microspheres can be harvested by choosing different non-solvent and its amount as well as incorporating polymeric additives. EXPERIMENTS The influences of the solution concentration, weight ratio between the non-solvent and the copolymer, and the polymeric additives on the surface morphology and the wettability of the electro-sprayed products were systematically studied. FINDINGS Surface pores and/or asperities on the microsphere surface were mainly caused by the non-solvent induced phase separation (NIPS) and subsequent evaporation of the non-solvent during electro-spraying. With increasing polymer solution concentration, the microsphere was gradually changed to the bead-on-string geometry and finally to a nanofiber form, leading to a sustained decrease of the contact angle (CA). It was found that the substrate coatings derived from the microspheres possessing hierarchical surface pores or dense asperities had high surface roughness and super-hydrophobicity with CAs larger than 150° while sliding angles smaller than 10°; but coatings composed of microspheres with smooth surfaces gave relatively low CAs.

Facile preparation of super-hydrophobic nanofibrous membrane for oil/water separation in a harsh environment

Oil removal or oil/water separation from the industrial waste water especially under harsh environment such as acid and alkali solutions have now been becoming an urgent task for human being. Here, flexible nanofibrous membrane with super-hydrophobicity/super-oleophilicity was prepared through a facile one-step solution-immersion approach, i.e., the poly(vinylidene fluoride) nanofiber mat modified with methyltrichlorosilane (MTS). The nanostructured polysiloxane with different morphologies including the ultrathin cylindrical wires and particles, were present on the nanofiber surface after MTS hydrolysis and subsequent condensation, which significantly enhanced the surface roughness and hence the hydrophobicity of the membrane. The influence of MTS concentration in the n-hexane solution and the hydrolysis time of MTS on the morphology of polysiloxane decorated nanofiber and hence the super-hydrophobicity was investigated in detail. The super-hydrophobic nanofibrous membrane could repel hot water and corrosive solutions, and the contact angle maintained around 150° with a pH ranging from 1 to 13. It was found that the oil/water separation with a high flux and efficiency was achieved by using the nanofibrous membrane that could not only separate the oil with the pure water and hot water but also the corrosive solution including the salt, acid and alkali solution. The organic/inorganic hybrid nanofibrous membrane may have find its potential applications in oil/water separation under a harsh environment.