| 초록 |
We investigate the effect of hard additives, i.e., magnetic and metal nanoparticles (NPs), on the ordered morphology of block copolymers by varying NP concentration. In order to characterize the structural change of the block copolymers associated with different NP loadings small-angle x-ray scattering and transmission electron microscopy were performed. Monodisperse maghemite (γ-Fe2O3) and silver NPs with surfaces modified with oleic acids have been synthesized and two PS-b-PI diblock copolymers showing lamellar and cylindrical morphologies were used as structure-directing matrices for the NPs. As the NP concentration is increased, domains of NP aggregates were observed for both magnetic and metal NPs. In the case of PS-b-PI / silver NPs mixtures with weak particle-particle interactions, the ordered morphology of the block copolymers loses their long-range order with the increase in NP concentration. It is, however, surprising to note that regular lattice-like aggregates with γ-Fe2O3 NPs induce an intriguing morphological transition from the hexagonal cylinders to the body-centered cubic spheres via undulated cylinders for the cylinder-forming PS-b-PI, which does not show such an order-order transition without NPs. The interplay between magnetic NPs and block copolymers was also tested with different size of magnetic NPs and also with different molecular weight of PS-b-PIs. We also demonstrate the preferred orientation of anisotropic microdomains of PS-b-PIs and the epitaxial morphological transition in the presence of magnetic NP aggregates. PS-b-PI diblock copolymers with a small difference in polarities of the two blocks, which is known to be difficult to orient by applying external fields such as electric or magnetic field, were shown to be aligned and even to go through an epitaxial morphological transition by the lattice-like magnetic NP aggregates under magnetic field. This result could add more flexibility in the structural control and orientation of block templates opening up new applications in the future. |
