PAN-pyrene-micelle based sensors for metal ions

A new method of preparing solid nanostructured polyelectrolyte films through self-assembly at the air/solution interface was discovered by our group figure.1,2 These films form spontaneously through interactions between water-soluble neutral polymers with polarisable groups, and surfactant micelles or vesicles with a positive charge.3 This new film formation technique was used to incorporate 1-(2-Pyridylazo)-2-naphthol (PAN) and pyrene in our novel polyelectrolyte/surfactants films. By trapping these species within the micelles in the films we aim to prepare solid fluorescent metal ion sensors which could be used for simple dip-stick testing for metal ions in aqueous solutions. Our work has so far concentrated on films formed from polyethylenimine (PEI) with cationic surfactants benzyldimethylhexadecylammonium bromide (BDHAB) and cetylpyridinium bromide (CpBr). These surfactants have aromatic groups in the headgroup which have been shown to enhance encapsulation of aromatic species such as pyrene. The films have an ordered mesostructure consisting of a surfactant liquid crystalline phase in a polymer hydrogel matrix. These films can be crosslinked at room temperature under ambient conditions by including ethylene glycol diglycidyl ether in the subphase solutions. This allows the films to be removed from the solution surface on an open mesh for drying or transfer onto a substrate. Dried films retain their mesoscale structure.4 We have shown using neutron reflectivity and small angle scattering that hydrophobic molecules can be encapsulated within these films inside the micelles.5 The species PAN is a well known chelating agent for transition metal ions. When used with pyrene in micellar systems the fluorescence response of pyrene is modified in a quantitative manner when PAN is bound to metal ions.6 The response can thus be calibrated and used as a fluorescence sensor. I will present small angle neutron scattering, neutron reflectivity and small angle X-ray scattering results to characterise the nanostructured PAN/pyrene containing films. The results demonstrate that the polymer hydrogel films contain micelles arranged in a 2D hexagonal nanostructure with strong evidence that PAN and pyrene are encapsulated inside the surfactants micelles. In current work calibration of these new materials as solid state metal ion sensors and their application to measurements of ion content in water solution is continuing and these experiments will also be presented.

References
1. KJ Edler, A Goldar, T Brennan, S Roser Chem. Commun. 2003, 1724.
2. BMD O'Driscoll, E Milsom, C FernandezMartin, L White, S Roser, KJ Edler Macromol 2005 38 8785.
3. BMD O'Driscoll, C Fernandez-Martin, R Wilson, S Roser, KJ Edler J Phys Chem B 2006, 110,5330
4. BMD O'Driscoll, EA Nickels, KJ Edler Chem. Commun. 2007, 1068
5. BMD O'Driscoll, AM Hawley, KJ Edler J. Colloid Interface Sci. 2008, 317, 585.
7. A Perez-Gramatges, A Chatt J. Radioanalytical Nuclear Chem. 2006, 269, 491.