Unveiling the mechanism of the location of the grafted nanoparticles in a lamellar-forming block copolymer

Through coarse-grained molecular-dynamic simulation of polymer-grafted nanoparticles in a lamellar forming diblock copolymer (BCP), we systematically study the effects of the grafting density (Ng), the compatibility between the grafted chains and the A-block of BCPs (εgA), and the NPs number (N) on the distance (D) of the NPs from the interface by proposing a novel characterization parameters of the orientation and distribution of the grafted chains. The nanoparticle gradually migrates away from the interface and into the A-block region with the increase of εgA for all studied Ng, while slightly returns towards the interface at high εgA and great Ng, which is the first observation of non-monotonic migration at the molecular level. We ascribe the reason of this to the behavior of the grafted chains that are near the interface. Furthermore, we classify the grafted chains into three types along the normal direction of the interface and the migration process is illustrated by the distribution and orientation of the different types of grafted chains, together with the radial distribution function between the NP and the A-block chains. We observe the formation of the NPs layers parallel to the interface for N<20, and a similar non-monotonic migration of the layers is as well observed. The D is the largest for a small N because of the excluded volume effects between the nanoparticles. Increasing Ng and N pushes the neighboring NPs layers towards the interface due to the mutual repulsion. Generally, this study may shed some light on how to better understand and design high performance polymer nanocomposites with tunable location of NPs.