NOVELTY - Nanoparticle dispersion (d1) comprises (a) an aqueous liquid medium, (b) an ionic liquid-based stabilizer in the liquid medium, where the stabilizer comprises an aromatic heterocyclic ring having at least one quaternary ammonium cation in the ring, a counter anion to the quaternary ammonium cation, and optionally a surfactant moiety covalently bound to the aromatic heterocyclic ring, and the stabilizer is in the form of a polymer comprising the aromatic heterocyclic rings as pendant groups from the polymer backbone and (c) nanoparticles dispersed in the liquid medium.    USE - The dispersion is useful for: forming a nanoparticle composite film (claimed) that is used to create electrical components such as resistors, capacitors, transistors, inductors, and microchips; and reducing oxygen and serving as a cathode in fuel cells.    ADVANTAGE - The dispersion: provides composite film that imparts improved electrical conductivity and/or thermal conductivity properties; and is stable.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a nanoparticle dispersion (d2) comprising (a1) aqueous liquid medium, (b1) ionic liquid-based stabilizer comprising the aromatic heterocyclic ring, counter anion and ethylenically reactive surfactant moiety covalently bound to the aromatic heterocyclic ring, where the stabilizer is in the form of an ionic liquid surfactant comprising the aromatic heterocyclic ring, counter anion, and the surfactant moiety and (c1) nanoparticles dispersed in the aqueous liquid medium;    (2) forming (f1) a nanoparticle dispersion, comprising (a2) providing the aqueous liquid medium, (b2) adding ionic liquid-based stabilizer and nanoparticles to the aqueous liquid medium to form pre-dispersion comprising the aqueous liquid medium, ionic liquid-based stabilizer, and the nanoparticles, where the ionic liquid-based stabilizer comprises aromatic heterocyclic ring, counter anion, and optionally a surfactant moiety, and the stabilizer is alternatively in the form of a polymer comprising the aromatic heterocyclic rings as pendant groups from the polymer backbone or an ionic liquid surfactant comprising the aromatic heterocyclic ring, the counter anion, and an ethylenically reactive surfactant moiety as the surfactant moiety and (c2) shearing the pre-dispersion to form a nanoparticle dispersion comprising the aqueous liquid medium, the ionic liquid-based stabilizer in the liquid medium, and the nanoparticles dispersed in the aqueous liquid medium;    (3) forming (f2) a nanoparticle composite film comprising providing the nanoparticle dispersion (d1), applying the nanoparticle dispersion to a substrate and removing at least a portion of the aqueous liquid medium to form a film adhered to the substrate, where the film comprises the nanoparticles and the ionic liquid-based stabilizer stabilizing adjacent nanoparticles in the film; and    (4) forming (f3) a nanoparticle composite film comprising providing the nanoparticle dispersion (d2), applying the nanoparticle dispersion to a substrate, removing at least a portion of the aqueous liquid medium to form a film adhered to the substrate, where the film comprises the nanoparticles and the ionic liquid-based stabilizer stabilizing adjacent nanoparticles in the film and optionally curing the ionic liquid surfactant to form a polymeric ionic liquid-based stabilizer in the film.