(628n) Towards AN IMPROVED Design for Nanoporous Polymeric MEMBRANES for Liquid Separations

Porous materials, in particular porous membranes, have generated immense interest in the last years due to a broad range of applications including photonic band gap materials, solid electrolytes, advanced filters in membrane technology, and in biological sciences. Much attention has been devoted to developing new fabrication processes and novel porous materials for these applications. Membrane performance depends to a great extent on the size of the pores, the width of the pore size distribution, and in general, of the overall membrane structure. Methods that allow for a detailed control of these parameters at the nano scale are therefore highly desirable [1]. In this work, new polymeric porous membranes with ordered structure were fabricated from templates made from silica particles. Silica particles were synthesized following the Stöber-Fink-Bohn [2] methods. The templates were obtained by self-assembly technique. For this technique, suspensions of silica particles in ethanol were used to create the deposits. Two different polymers were tested to fabricate membranes: polystyrene (PS) and the diethyleneglycol dimethacrylate (DEGDMA)/urethane dimethacrylate (UDMA) copolymer. Monomers were infiltrated in the templates by capillarity and then they were polymerized in an oven at T = 80 ºC. Silica particles were removed by submerging the system (template + polymeric film) in a 5% solution of hydrofluoric acid, forming a porous material. Templates and porous films were observed by SEM to analyze the pore morphology. The observed structures did not suggest significant particle reaccommodation during the monomer filling process. The films exhibited a high surface porosity, resulting from the contact points of particles and glass slides during the infiltration process.

Water filtration experiments were performed in order to demonstrate pore connectivity in the films. PS films exhibited extreme fragility and did not resist regular handling. For this reason, only poly(DEGDMA/UDMA) films could be measured. Permeability of the poly(DEGDMA/UDMA) films was comparable to commercially available membranes.

Brunauer–Emmett–Teller adsorption isotherm (BET) was applied to measure specific area and pore distributions of the membranes.

The membranes were also characterized in terms of solute retention. Molecular weight cut off profiles using dextrans of different molecular weights were obtained.

By chemical modification of the polymeric material, these structures can be used to fabricate sensors and membranes to detect or to retain organic substances or metals in water.

[1] M. Mulder, Basic Principles of Membrane Technology, 2nd ed., Kluwer Academic Publishers, Dordrecht, 2004.

[2] W. Stober, A. Fink, E. Bohn, J. of Colloid and Interface Sci., 26 (1968) 62.