Role of Solvent In Pore Structure of Mixed Matrix Membranes

The incorporation of nanomaterials into membranes has been used for a wide range of organic and inorganic membranes to change specific physical and chemical properties of the original membrane material.  These mixed matrix membranes are designed such that the nanomaterial imparts improved structural stability and performance.  While the primary goal in gas separations has been to change specific gas transport properties, the use of mixed matrix membranes for water filtration has focused on improving both the transport and the function of the membrane.  In the reverse osmosis filtration regime, nanoparticles such as zeolites have been used within the thin aromatic polyamide layer to improve salt rejection and water transport (1), while in the ultra- and microfiltration regimes, nanoparticle materials such as iron, silver, titanium dioxide, and C₆₀ fullerenes have been used to change transport properties or make the membranes reactive towards foulant layers or dissolved water contaminants (2-5). 

In a polymeric membrane produced by phase inversion from a solvent (e.g., dimethylacetamide) to a non-solvent (e.g., water), variations in the solvent and non-solvent can cause changes in the internal pore structure.  In addition to changing membrane mechanical and transport properties, the incorporation of nanoparticles into a polymer-based membrane adds an additional component of the casting solution that can, in some cases, also alter the internal pore structure of the membrane.  The role of nanomaterials in pore formation during phase inversion is not well-understood, and the effect of solvent and non-solvent choice on pore structure has not been well-studied for mixed matrix membranes.

This talk will focus on polyether sulfone (PES)-based mixed matrix membranes produced by phase inversion. Recent work in our group has shown that the incorporation of iron-based nanoparticles can drastically change the internal pore structure of these mixed matrix membranes.  In contrast, work on other hydrophilic, metal-based nanoparticles (3) and PES has not resulted in similar changes to membrane pore structure.  To separate the role of the solvent and non-solvent from the role of the nanoparticle, several solvents with a range of enthalpies of mixing with water are evaluated for the same concentration of nanoparticles in the casting solution.  Morphological changes to internal and surface pore structure will be discussed, along with an initial evaluation of membrane performance based on pure water flux of cast membranes.

1)         Lind, M. L.; Suk, D. E.; Nguyen, T. V.; Hoek, E. M. V. Environmental Science & Technology 2010, 44, 8230.

(2)        Taurozzi, J. S.; Crock, C. A.; Tarabara, V. V. Desalination 2011, 269, 111.

(3)        Taurozzi, J. S.; Arul, H.; Bosak, V. Z.; Burban, A. F.; Voice, T. C.; Bruening, M. L.; Tarabara, V. V. Journal of Membrane Science 2008, 325, 58.

(4)        Yang, Y. N.; Zhang, H. X.; Wang, P.; Zheng, Q. Z.; Li, J. Journal of Membrane Science 2007, 288, 231.

(5)        Xu, J.; Bhattacharyya, D. Industrial & Engineering Chemistry Research 2007, 46, 2348.