Nanometric ZnO, sp. surface 42.5 m(2)/g, xi < O over pH = 2.5-11.5. isoelec. at pH 3.7 (dispersants shifted the pH to 10 and made xi > O), enabled the amt. of ZnO to be reduced by 60%, to 0.5-1 wt. part, in SBR and NBR, as compared with micrometric ZnO, provided alkylammonium salts like didodecyldimethylammonium bromide were added to aid ZnO to disperse and to disintegrate ZnO nanoparticle clusters in elastomer matrix. Vulcanization rates and crosslinking ds. were higher. The longer the alkyl chain, the more effective the dispersant toward the ZnO surface.