Preparation Of Isoporous Membranes Via The Breath Figure Method: Research Of Solid Substrate

Polymer membranes have been widely applied in fields of environment, food and health care. Microfiltration and ultrafiltration are based on the mechanism of size exclusion. Membranes prepared by the phase inversion process are characterized of pores size polydispersity and tortuous channels, which hinder their separation efficiency. Isoporous membranes with pore size monodisperse and through pores possess the advantages of high separation accuracy and low transmembrane pressure, thus they have attracted much attention in recent years. So far, techniques for fabricating isoporous membranes include track etch, micro processing method, self-assembly approaches such as particle templating, breath figure method, and microphase separation of block copolymers. The breath figure method provides an economical, convenient route to realize orderly arrayed pores with size dynamically controlled. However, by the breath figure method, fabrication on a solid substrate generally results in dead-end pores. Through-pore membranes can be only prepared on air/water interface or air/ice interface, which is not favourable to large-scale production.A facile strategy has been proposed to prepare isoporous membranes on versatile solid substrates. The procedure is described as follows. First, a layer of hydrophilic polymer is spin-coated onto solid substrates. Second, breath figure arrays are formed on the hydrophilic polymer layer. Third, the layer is soluted in an aqueous solution, and thus isoporous membrane is detached from the substrates. Last, isoporous membrane is transferred to a macroporous support to produce a composite membrane. The hydrophilic polymer coating as a multifunctional interlayer promotes the spreading of membrane-forming solutions, enables the construction of through pores, and simplifies the transfer to target substrates. The versatility of the proposed strategy is verified by using different substrates including highly hydrophobic polytetrafluoroethylene film and using different water-soluble polymers as the interlayer. Furthermore, the high-resolution separation performance of the isoporous composite membranes has been demonstrated by the filtration of yeasts under gravitational pressure.Based on polydopamine deposition, a new approach to the formation of multifunctional interlayer was proposed. Surface of gradient hydrophilicity was constructed through modification of the polydopamine layer, applying to investigate the effect of hydrophilicity on the morphology of isoporous membranes. It reveals that the through pore ratios of isoporous membranes markedly decrease with increasing hydrophobicity. While on a fluorinated substrate, the hydrophobicity suppresses the spreading of membrane-forming solution, as a result, the thickness of membrane-forming solution increases, and the pore size of membrane increases. It demonstrates that the morphologies of isoporous membranes can be regulated by changing the chemical properties of solid substrates.