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Fouling is a common challenge to all membrane-based separation technologies. The current study demonstrated an antifouling membrane with a superhydrophilic but oleophobic (in air) characteristic, which was achieved through covalently tethering heterogeneously tailored two-dimensional layered double hydroxide (LDH) nanosheets to a polyvinylidene fluoride membrane surface. The nanosheets were in situ grafted with alternately arranged sodium 1-dodecanesulfonate (SDS) and 3-aminopropyltriethoxysilane (APTS) chains during preparation. Poly(methacrylic acid) (PMAA) was previously grafted on the membrane via plasma induced graft copolymerization as anchor sites for nanosheet binding. With a simple dip-coating operation, the surface-tailored LDH nanosheets could be bound to the membrane via cross-linking between the amine groups of APTS and carboxyl groups of PMAA. Ultimately, the long hydrophobic SDS and short hydrophilic APTS chains on the nanosheets formed a heterogeneous and infiltration selective (due to steric exclusion) surface on the membrane. As a result, the hydrophilic moieties on the membrane surface were much more accessible to water than to liquids of larger molecular size, thereby bringing about the superhydrophilic but oleophobic characteristic. The functionalization gave rise to both significantly enhanced wettability and hydrophilicity of the membrane, mainly owing to the increase of the electron donor component of surface energy (γAB−). Additionally, the functionalized membrane obtained a greater permeability without compromising its selectivity. Furthermore, as verified in both filtration tests with synthetic and practical foulant solutions, the superhydrophilic and oleophobic characteristic endowed the functionalized membrane with conspicuously greater cleaning efficiency and excellent capability in resisting irreversible fouling, suggesting promising applications in various fields.

Fouling is widely recognized as a main barrier to the sustainable development of membrane separation technologies. This study demonstrated a hierarchically textured superhydrophilic membrane, which was fabricated via nanocasting and post-fabrication grafting of surface-tailored silica nanoparticles. Nanocasting, using a prepared polydimethylsiloxane plate as an intermediate transfer template, gave rise to a micro-scaled surface texture resembling the surface pattern of a stainless-steel mesh. The resultant textured membrane surface was then sequentially grafted with poly(methacrylic acid) and surface-tailored silica nanoparticles through plasma induced graft copolymerization and self-assembly dip-coating, respectively, thereby resulting in an extra nano-scaled nanoparticle layer. The appropriate hierarchical structure and high surface energy of the membrane surface enormously improved its affinity with water, thus rendering the resultant functionalized membrane (designated as textured_F) superhydrophilic (water contact angle instantly reduced to 0° upon contact). Compared with a commercial 0.22 μm membrane, the textured_F membrane exhibited a slightly higher permeability and a significantly improved rejection ability, probably owing to the dense silica nanoparticle layer which functioned as a selective barrier. Moreover, in the systematic multi-cycle filtration experiments with a practical membrane bioreactor supernatant, the textured_F membrane exhibited a ∼2.4 times higher cleaning efficiency than the commercial membrane, demonstrating a dramatically improved antifouling capability. This improvement was probably due to the superhydrophilic and hierarchical membrane surface, which potentially facilitated the formation of an in situ hydration layer and peripheral turbulent flow thus resisting the adhesion of foulants.

It is a major problem that ground wire breakage occurs due to the high temperature rise. And it is of great significance to study temperature rise characteristics of its hotspot. A 3-D finite element model of contact fracture between the ground wire and preformed armor rod is set up in the paper and firstly the equivalent method of contact resistance is analyzed and determined. Based on this model, influence of skin effect on contact resistance of contact fracture area is studied. Furthermore, effect of contact resistance and short circuit current on transient temperature rise in the contact fracture area are also analyzed. It can be concluded that the deeper the degree of skin effect, the greater the contact resistance and temperature rise. And with the combined effect of contact resistance and short circuit current, the possibility of direct fusing of the ground wire is proved. Moreover, temperature rise ratio of the ground wire which is away from contact fracture is much less than that of contact fracture area.