272493 Magnetically Responsive Membranes As Micromixers and Nanoheaters

Tuesday, October 30, 2012: 3:15 PM
401 (Convention Center )
Qian Yang1, Heath Himstedt2, Xianghong Qian1,3 and S. Ranil Wickramasinghe4, (1)Ralph E Martin Department of Chemical Engineering, University of Arkansas, Fayetteville, AR, (2)Chemical and Biological Engineering, Colorado State Univeristy, Fort Collins, CO, (3)Ralph E Martin Department of Chemical Engineering, University of Arkansas, Fayetteville, AR, (4)Department of Chemical Engineering, University of Arkansas, Fayetteville, AR

Magnetically Responsive Membranes as Micromixers and Nanoheaters

 

 

Qian YANG1, Heath H. HIMSTEDT2, Xianghong QIAN1, S. Ranil WICKRAMASINGHE1

1 Ralph E Martin Department of Chemical Engineering, University of Arkansas, Fayetteville 72701, USA; 2Department OF Chemical and Biological Engineering, Colorado State University, Fort Collins, CO 80523.

Two of the most important factors limiting the use of membrane technology are concentration polarization and membrane fouling.1 Efforts have been made to solve these problems by means of optimizing module design or inducing mixing during operation, pretreatment of the feed and surface modification of the membrane. Feed pretreatment can only postpone the decline of membrane performance while surface modification is not able to suppress concentration polarization.2 Therefore, there is still a need to find an efficient way to improve anti-fouling property of membranes and to reduce concentration polarization.

Herein, we report a novel approach to solve these problems by attaching magnetically responsive nanoparticles to the membrane surface. As can be seen from Figure 1, polymers (polyHEMA and poly NIPAAm) were grafted to membrane surfaces by surface initiated ATRP. After that, the bromine groups at chain ends were converted primary amine by Gabriel synthesis and then used for attaching carboxyl groups covered superparamagnetic Fe3O4 nanoparticles. The chain/nanoparticle density can be controlled by varying the ratio of active to inactive ATRP initiator in the initiator immobilization step. The modification and nanoparticle immobilization were monitored by XPS and SEM. XPS confirmed each step of modification. SEM images showed that the nanoparticles were successfully attached to the membrane surface and the density can be tuned in a broad range (see Figure 2).

Figure 1. Schematic representation for the grafting of polyHEMA and immobilization of magnetic nan-oparticles. Figure 2. SEM images showing magnetic nanoparticles immobilized on membrane surface with high (left) and low (right) density.

With nanoparticles attached to the end of polyHEMA, the polymer chains acted as micromixers under oscillating magnetic field and mixing above the membrane surface was observed. This mixing resulted in a significantly improved membrane performance (flux and salt rejection) which can be ascribed to reduced concentration polarization. Tuning the space between these micromixers by diluting nanoparticle density leaded to optimization of membrane performance. On the other hand, with polyNIPAAm on the surface, nanoparticles were used as nanoheater in the presence of magnetic field to exert temperature change below and above LCST of this thermo-responsive polymer. Subsequently conformational changes of polyNIPAAm leaded to a dense/loose layer structure transformation on the membrane surface and changed membrane performance. This result demonstrated the possibility of using external magnetic field to control the membrane performance which is promising for industrial applications to realize instantaneous product control without interrupting the production line.

References

1. R.W. Baker, Membrane Technology and Applications, 2nd ed.; John Wiley: Chichester, (2004).

2. D. Rana and T. Matsuura, Chem. Rev., 110, 2448 (2010).


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