| 초록 |
Nanostructured organic-inorganic hybrid material is one of the most promising and rapidly emerging research areas in materials chemistry such as optical materials, electromagnetic devices, metal catalysts, and novel structural features, which arise from the synergistic interaction of the individual constituents. Particularly, polymer-nanoparticle hybrids (hereafter nanohybrids) offer diverse scientific challenges, combining ideas from colloid science, polymer physics and chemistry. Nanohybrids become more intriguing when block copolymers are used as a structure-directing matrix due to their ability to microphase-separate into ordered structures on the length scale of tens of nanometers. The addition of nanoparticles can change the characteristic dimensions, or even the morphology, of the ordered block copolymer structures since their miscibility with a polymer matrix and their resulting stability are crucial factors. Therefore a desirable morphology can be attained by controlling the copolymer composition, the volume fraction of the particles, the interaction between the particles and the blocks, etc. In particular, for nanohybrids containing ferromagnetic materials such as iron and cobalt magnetic interactions between the nanoparticles may cause the clustering since the block copolymer is often weakly bound to the nanoparticles. Consequently the novel change in ordered morphology can be expected and those fascinating magnetic properties have fueled both fundamental and applied studies. In this study, we investigate the effect of hard additives, i.e., magnetic nanoparticles, on the phase behavior of polystyrene-block-polyisoprene (PS-b-PI) diblock copolymers by varing the size of nanoparticles (6 nm and 14 nm). For the design of multicomponent materials with spatially defined order of different components, two PS-b-PI diblock copolymers showing lamellar (SI1) and cylindrical (SI2) morphologies are used as structure-directing matrices for the nanoparticle arrangement. Fine maghemite (γ-Fe2O3) particles with surfaces modified by oleic acid have been synthesized not only for greater solubility but also to prevent particle aggregation. Two different solvents, hexane and toluene, were used to prepare film specimens by static casting and the interactions between mesophase-forming copolymers and nanoscopic particles can lead to highly organized hybrid materials. Notably, the morphology of such composites strongly depends on the preparation conditions as well as the characteristics of templating copolymers. The nanoparticles were selectively incorporated into the PI domains under hexane condition, while they were preferentially aggregated when toluene is used. Particularly, in the toluene condition, we observed the well-defined body centered cubic structure for SI2 as well as the undulating lamellar morphology for SI1. The structural information obtained from X-ray scattering is in good agreement with the transmission electron microscopy images and differential scanning calorimetry results. |
