New Approach to the Synthesis of Exfoliated Polymer/Graphite Nanocomposites by Miniemulsion Polymerization Using Functionalized Graphene

A new method is described for the synthesis of exfoliated polymer nanocomposites made with modified graphite oxide (GO) using a miniemulsion polymerization technique. GO was synthesized and then modified with a reactive surfactant, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), which widened the gap between the graphene layers and facilitated monomer intercalation into the GO nanogalleries. The AMPS-modified GO was emulsified in the presence of styrene and butyl acrylate monomers, a surfactant (sodium dodecylbenzenesulfonate), and a hydrophobe (hexadecane). The stable miniemulsions were polymerized to afford encapsulated poly(styrene-butyl acrylate) (poly(S-BA))/GO nanocomposite latex particles. The exfoliated structure of the nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM revealed that graphene oxide nanosheets were largely exfoliated (about 2-5 nm thick) in the resultant films obtained from the synthesized nanocomposite latices. Examination of the nanostructure of the obtained nanocomposites by XRD analysis confirmed the formation of exfoliated graphene oxide nanoplatelets. The thermal stability and mechanical properties of the nanocomposites were evaluated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). TGA showed that all the prepared nanocomposites exhibited enhanced thermal stability relative to the neat poly(S-BA) copolymer. DMA also revealed that the glass transition temperature of poly(S-BA) in the nanocomposites increased significantly in the presence of modified GO relative to pure copolymer. Furthermore, the nanocomposites had improved storage and loss modulus only at relatively high GO content (i.e., Sand 6 wt % relative to monomer).