NAFION ORMOSIL HYBRIDS VIA IN-SITU SOL-GEL REACTIONS .3. PYRENE FLUORESCENCE PROBE INVESTIGATIONS OF NANOSCALE ENVIRONMENT/

Pyrene (Py) photophysical probes were used to interrogate structural d iversity within [1] Nafion/[silicon oxide] and [2] Nafion/[ORMOSIL] hy brids. The interior of the silicon oxide phase in [1] has the most pol ar environment wherein Py is trapped in silicon oxide cages in the vic inity of -SO3- groups. Polar/nonpolar interphase regions in [1] are ne xt in order of decreasing polarity. The interior of the ORMOSIL phase in [2] displays lowest polarity, reflecting CH3 groups in Py-encapsula ting ORMOSIL cages, and the interphase ranks somewhat higher in polari ty. Water uptake is ordered: Nafion/ORMOSIL < unfilled Nafion-H+ < Naf ion/[silicon oxide]. The hydrophilicity of unfilled Nafion-H+ is adjus table by tailoring the organic content of the incorporated sol-gel-der ived nanophase as polarity determined from fluorescence emission and w ater uptake correlate well. Fluorescence emission of Py monitored nano structural polarity shifts that result from secondary in situ gel grow th induced by annealing. Additional condensation of SiOH groups and li beration of volatiles is promoted by increasing temperature/time, as e videnced by diminishing polarity. Polarity decrease with annealing is more profound for Nafion/[ORMOSIL incorporating Py] than for Nafion/[s ilicon oxide incorporating Py] as polar solvents are removed more easi ly from the less polar ORMOSIL nanophase.