An orientationally ordered hierarchical exfoliated clay-block copolymer nanocomposite

Creation of an orientationally ordered hierarchical nanocomposite can be done by the preferential insertion of individual polymer-covered clay layers into block copolymer (BCP) microdomains-in the present instance, PS-functionalized silicate layers into the polystyrene (PS) domains of a styrenebutadiene -styrene triblock copolymer (SBS). We present here the method required to achieve such an ordered block copolymer-nanoparticle composite and report preliminary mechanical properties. PS is grafted-to or polymerized-from individual clay sheets in order to provide a neutral enthalpic interaction between the PS chains on the clay layers and the PS blocks in the SBS. The molecular weight of the PS chains tethered to the clay was varied, and we show that higher molecular weight is critical in obtaining individual clay sheets dispersed in the SBS matrix. When exfoliated, the clay sheets serve as a template for the lamellar domains. Because of their large areal dimensions and concentration, the clay particles likely form a discotic nematic that is responsible for the observed orientational flipping transition of the BCP layers during the roll-cast process. We also show through experiments and simulations that the mechanical properties of these anisotropic hierarchical nanocomposites are not significantly changed by the insertion of 2 wt % of the clay sheets for deformation parallel to the lamellae.