Nanoparticles with dual properties of magnetic susceptibility and ionic conductivity were synthesized for application in proton exchange membranes (PEM). The particles were composite in nature, consisting of gamma-Fe2O3 and sulfonated crosslinked polystyrene. The synthesis was carried out using emulsion polymerization with various feed compositions ranging from 0 to 23 wt% ionic monomer and 8-11 wt% crosslinking monomer. The synthesized particles were in the size range of 230-340 nm and had polymer content of about 75-80%. A very unusual morphology of iron oxide localization was observed in the composite particles, and a model is proposed to explain such a structure. The particles had considerable magnetic susceptibility, and aligned easily in a sulfonated poly (ether ketone ketone) (SPEKK) matrix under magnetic field of 0.1 Tesla. The membrane with composite particles had lower ion-exchange capacity (IEC) compared to plain SPEKK (2.4 meq/g), due to the lower IEC (0.35 meq/g) of the particles used. However, a proton conductivity of about 0.0043 +/- 0.0028 S/cm was observed by aligning the particles in the SPEKK matrix. By randomly dispersing the particles, the conductivity was about 0.0020 +/- 0.0018 S/cm. The water and methanol uptakes were similar for both kinds of membranes and were about 23% and 18%, respectively. The use of magnetic fields for aligning the proton conducting domains was successfully demonstrated. (c) 2007 Elsevier B.V. All rights reserved.