Surfactant Effects on Morphology-Properties Relationships of Silver-poly(styrene-b-isoprene-b-styrene) Block Copolymer Nanocomposites

摘要

Good dispersion of silver nanoparticles in poly(styrene-b-isoprene-b-styrene) block copolymer matrix has been achieved by adding dodecanethiol as surfactant to lower the high surface energy of metal nanoparticles. First, the influence of surfactant in the cylindrical nanostructure of neat block copolymer matrix has been analyzed. Taking into account the high solubility between dodecanethiol and the PS block of the SIS block copolymer, when silver nanoparticles and surfactant have been added to the block copolymer matrix its morphology changes from cylindrical to lamellar nanostructure. For the nanocomposite without surfactant, the block copolymer matrix loses its capability to self-assemble in lamellar nanostructure and in this case, agglomeration of silver nanoparticles occurs. Rheological, mechanical and morphological analysis were carried out in order to study the optimal content of surfactant necessary to obtain well-dispersed nanoparticles without worsen the final properties of the nanocomposite. The best silver/dodecanethiol w/w ratio appears to be 1, as confirmed by UV-Vis analysis. Moreover, semi-empirical models, such as Guth and Gold, and Halpin-Tsai, have been used in order to both predict and verify experimental tensile modulus of the obtained nanocomposites. The Guth and Gold equation, applicable to elastomers filled with spherical nanoparticles, provides a result closer to the experimental values than Halpin-Tsai model.