Styrene butadiene copolymer (SBR)-SiO2 nanoparticles with core shell morphology were prepared via differential microemulsion polymerization. The effects of silica loading, monomer to water ratio, surfactant concentration and initiator concentration on monomer conversion, particle size, particle size distribution, grafting efficiency and silica encapsulation efficiency were investigated. A high monomer conversion of 86.6% and SBR-SiO2 nanoparticles with a size range of 20-50 nm, with a narrow size distribution and high grafting efficiency of 75.5% were obtained at a low surfactant concentration of 3 wt.% based on monomer. The obtained SBR-SiO2 nanoparticles exhibited spherical morphology with SiO2 as the core and SBR as the shell as confirmed by TEM micrographs. Well-dispersed SBR-SiO2 nanoparticles were successfully synthesized by differential microemulsion polymerization at a low surfactant concentration under optimum condition. A nanocomposite membrane prepared from natural rubber (NR) and a SBR-SiO2 emulsion was tested for its mechanical properties and the pervaporation of water-ethanol mixtures. The flux and selectivity of NR/SBR SiO2 nanocomposite membranes were reported as a function of SBR-SiO2 loading and water concentration. The NR/SBR SiO2 membranes can be used to separate water from mixtures of water/ethanol with high water selectivity. (C) 2014 Elsevier B.V. All rights reserved.