Synthesis and characterization of sulfonated poly(styrene-b-(ethylene-ran-butylene)-b-styrene)/(strontium titanate) nanocomposites

Nanocomposite films were prepared via syntheses of SrTiO3 nanoparticles in films of sulfonated poly(styrene-b-ethylene-co-butylene-b-styrene) (sSEBS) block copolymer templates. SrTiO3 ionic and alkoxide precursors permeated selectively into styrene domains in which formation and growth of crystalline nanoparticles occurred through hydrolysis-precipitation reactions. FTIR spectra verified SrTiO3 composition and WAXD patterns identified crystalline SrTiO3 within the templates. AFM images for both unfilled sSEBS and sSEBS/SrTiO3 microtomed films showed mesophase separation characterized by lamellar morphologies suggesting that SrTiO3 particle insertion did not alter template morphology. Uniform distribution of Ti and Sr along the nanocomposite internal film cross sections and external surfaces was seen using ESEM/EDX. TEM images showed clusters of parallel SrTiO3 rods in sulfonated styrene domains. Agreement of SrTiO3 rod width in TEM images with domain size in AFM images supports the template hypothesis. Selected area electron diffraction studies of SrTiO3 clusters inside sSEBS/SrTiO3 provided direct identification of in situ formation of crystalline SrTiO3 particles. WAXD studies demonstrated that in situ – grown particles have the same crystal structure as those produced outside the template. The frequency dependent broadband dielectric responses of these materials, both filled and unfilled, reflect strong polarizability that is more sensitive to degree of sulfonation than from insertion of SrTiO3 nanoparticles.