Zinc oxide (ZnO) nanoparticles assembled in one dimension to give rod-shaped morphology were synthesized. The effect of these ZnO nanoparticles (average particle size similar to 50 nm) as the curing agent for carboxylated nitrile rubber was studied with special attention to cure characteristics, mechanical properties, dynamic mechanical properties, and swelling. These results were compared with those of the conventional rubber grade ZnO. The study confirmed that the ZnO nanoparticles gave a better state of cure and higher maximum torque with a marginal decrease in optimum cure time and scorch time. The mechanical properties also showed an improvement. There was an increase in tensile strength by similar to 120%, elongation at break by similar to 20%, and modulus at 300% elongation by similar to 30% for the vulcanizate cured with ZnO nanoparticles, as compared with the one containing rubber grade ZnO. Dynamic mechanical analysis revealed that the vulcanizates exhibited two transitions-one occurring at lower temperature due to the T-g of the polymer, while the second at higher temperature corresponding to the hard phase arising due to the ionic structures. The second transition showed a peak broadening because of an increase in the points of interaction of ZnO nanoparticles with the matrix. The tan 6 peak showed a shift towards higher Tg in the case of ZnO nanoparticle-cured vulcanizate, indicating higher crosslinking density. This was further confirmed by volume fraction of rubber in the swollen gel and infrared spectroscopic studies. (c) 2007 Wiley Periodicals, Inc.