Magneto-responsive composite membranes for switchable molecular sieving

Magneto-responsive composite membranes for switchable molecular sieving

Axilin

Stimuli-responsive membranes which can adjust mass transfer and interfacial properties “on demand” have drawn large interest over the last few decades. Among all kinds of stimuli-responsive membranes, magneto-responsive membranes are especially interesting, as they can realize spatial, temporal and remote control and have great potential application in biomedical and microfluidics fields. Magnetic nanoparticles (MNPs) can generate heat when exposed to an alternating magnetic field (AMF), due to hysteresis and relaxation losses. When combined with thermo-responsive polymers, the heat generated by MNPs can trigger the phase or conformation change of polymer and therefore could be applied for controlled drug release and shape memory actuators. Poly(N-isopropylacrylamide) (PNIPAAm) is one of the most well-known thermo-responsive polymers, due to its pronounced phase change in response of temperature. Before, our group had developed PNIPAAm hydrogel pore-filled composite membrane, which demonstrates excellent thermo-responsive (macro)molecule size selectivity [1]. However, conventional thermal actuation by heating the entire feed is relatively slow and energy-consuming. Recently, it had also been shown that liquid permeability through membrane pores containing immobilized MNPs and grafted with linear PNIPAM chains can be reversibly switched by AFM, but due to large pore size, no molecule size selectivity had been achieved [2].

Here, our target is to design and prepare novel magneto-responsive separation membranes with remote switchable molecular sieving effect, by using iron oxide MNPs as localized heater and PNIPAAm hydrogel as sieving medium and actuator. Specifically, two different membrane types have been proposed and experimentally achieved. One type is magneto-hydrogel pore-filled membrane constructed by post modification of commercial polyethylene terephthalate (PET) track-etched membrane [3]. It was demonstrated that by manipulating AMF and thus controlling the heat generated by the incorporated MNPs, the micro-syneresis of PNIPAAm network can be locally triggered, and magneto-responsive molecule sieving can be achieved. The other type is polyethersulfone (PES) membrane containing prefabricated PNIPAAm nanogel and iron oxide MNPs fabricated by non-solvent induced phase separation. It had been expected that the molecular sieving performance of the membrane can be controlled by the swollen/shrunken state of PNIPAAm nanogel triggered by the heat generation of nearby MNPs. The feasibility of this approach was also demonstrated. Overall, important parameters affecting the construction of both kinds of membranes have been studied, their stimuli-responsive barrier properties including thermo- and magneto-responses have been investigated, and their molecular sieving effect in the ultrafiltration range has been evaluated. Based on the results, correlations between synthesis, structure and separation performance of the novel magneto-responsive membranes and their potential for applications are discussed.

References

  1. N. Adrus, M. Ulbricht, J. Mater. Chem. 2012, 22, 3088
  2. A. Gajda, M. Ulbricht, J. Mater. Chem. B 2014, 2, 1317
  3. X. Lin, R. Huang, M. Ulbricht, J. Mater. Chem. B 2016, 4, 867
  4. X. Lin, B. Nguyen Quoc, M. Ulbricht, ACS Applied Materials and Interfaces 2016, 8, 29001-29014
Funding: The work is supported by a Ph.D. scholarship of the Chinese Scholarship Council (CSC)

Contact:
Prof. Dr. Mathias Ulbricht