Magnetically Activated Micromixers for Separation Membranes

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• 作者：Heath H. Himstedt ; Qian Yang ; L. Prasad Dasi ; Xianghong Qian ; S. Ranil Wickramasinghe ; Mathias Ulbricht
• 刊名：Langmuir
• 出版年：2011
• 出版时间：May 3, 2011
• 年：2011
• 卷：27
• 期：9
• 页码：5574-5581
• 全文大小：1029K
• 年卷期：v.27,no.9(May 3, 2011)
• ISSN：1520-5827

文摘

Presented here is a radically novel approach to reduce concentration polarization and, potentially, also fouling by colloids present in aqueous feeds: magnetically responsive micromixing membranes. Hydrophilic polymer chains, poly(2-hydroxyethyl methacrylate) (PHEMA), were grafted via controlled surface-initiated atom transfer radical polymerization (SI-ATRP) on the surface of polyamide composite nanofiltration (NF) membranes and then end-capped with superparamagnetic iron oxide magnetite (Fe₃O₄) nanoparticles. The results of all functionalization steps, that is, bromide ATRP initiator immobilization, SI-ATRP, conversion of PHEMA end groups from bromide to amine, and carboxyl-functional Fe₃O₄ nanoparticle immobilization via peptide coupling, have been confirmed by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). These nanoparticles experience a magnetic force as well as a torque under an oscillating external magnetic field. It has been shown, using particle image velocimetry (PIV), that the resulting movement of the polymer brushes at certain magnetic field frequencies induces mixing directly above the membrane surface. Furthermore, it was demonstrated that with such membranes the NF performance could significantly be improved (increase of flux and salt rejection) by an oscillating magnetic field, which can be explained by a reduced concentration polarization in the boundary layer. However, the proof-of-concept presented here for the active alteration of macroscopic flow via surface-anchored micromixers based on polymer鈭抧anoparticle conjugates has much broader implications.