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Polyelectrolyte Brush on Nanoporous Membrane

Y. Ito*

Graduate School of Material Science, NAIST

This is an abstract for a poster to be presented at the Fifth Foresight Conference on Molecular Nanotechnology. The full paper is available here.

Various types of nanoporous materials have been developed. Here polyelectrolyte brushes were grafted on a nanoporous membrane to regulate the substance permeation through the pores in response to pH, temperature, oxireduction, or photo-irradiation. The conformation of polyelectrolyte chain is dependent upon the environmental conditions. In the case of poly(acrylic acid) grafting, the polymer chain is protonated and contracted in the regions of low pH; it is de-protonated and extended in regions of high pH. Therefore, the size of each pore, and thus the permeability through the membrane could be rapidly regualted by changing the pH change because the brush chains directly contact with environment.

In order to graft the polyelectrolyte chains to the surface, track-etch porous polycarbonate membrane (average pore diameter, 200 nm) was glow-discharged and poly(acrylic acid) was graft-polymerized on the membrane surface. The water permeation rate through the grafted membrane was high at low pH, but was reduced at neutral pH. These changes in permeation were reversible upon additional pH changes. To clarify the mechanism of permeability regulation of the polyelectrolyte brush system, an atomic force microscope was used to make and in situ observation of pore shape in an aqueous solution. The presence of pore was observed at low pH, but not at high pH. Thus the polyelectrolyte grafts behave like a gate to open and close the pores. In addition, in this system, the change in permeability change occurred within several seconds of pH change. The polyelectrolyte brushes were put in direct contact with their environment; this allowed them to respond quickly.

*Corresponding Address:
Yoshihiro Ito, Graduate School of Material Science, NAIST, 8916-5 Takayama-cho, Ikoma 630-01, JAPAN, ph: +81-743-72-5903, fax:+81-743-72-5903, email: yito@ms.aist-nara.ac.jp
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