Perpendicularly Oriented Block Copolymer Thin Films Induced by Neutral Star Copolymer Nanoparticles.

By introducing neutral star copolymers consisting of poly(styrene-r-methyl methacrylate) (PS-r-PMMA) arms, a perpendicular orientation of PS-b-PMMA microdomains in thin films could be achieved without any surface treatment. The star copolymers were synthesized by arm-first method in which short chain arms are cross-linked by employing a multifunctional coupling reagent via atom transfer radical polymerization. To find the optimal neutral composition for the perpendicular orientation, we varied the composition of MMA in PS-r-PMMA arms from 40 mol % to 80 mol %. It was found that the star copolymer having an overall PS and PMMA composition of 59:41 exhibits the well-ordered perpendicular orientation of lamellar structures after thermal annealing. Furthermore, we also prepared the deuterated star copolymers to trace them within PS-b-PMMA films along vertical direction by neutron reflectivity. In this case, it was observed that star copolymers were mainly located at the top surface and bottom interface of the films, thereby effectively neutralizing the surface/interfacial energy differences.

Nanoporous bicontinuous structures via addition of thermally-stable amphiphilic nanoparticles within block copolymer templates.

Herein, we fabricated the bicontinuous structures from nanocomposites of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer and the shell-cross-linked, thermally stable gold nanoparticles (Au NPs). The surface property of Au NPs was controlled with ligands containing various compositions of PS and PMMA so that the resulting Au NPs were selective to PS or PMMA block or nonselective (i.e., neutral) to both blocks. The amphiphilic Au NPs were also prepared by coating the surface of Au NPs with equimolar mixtures of PS and PMMA selective ligands. Consequently, it was found that the morphological behaviors of thermally annealed nanocomposites containing amphiphilic Au NPs and PS-b-PMMA were dramatically different from the case of neutral Au NPs that were coated with nonselective ligands. With increasing the amount of amphiphilic Au NPs, a transition from lamellar to bicontinuous structures was observed, whereas the neutral Au NPs were aggregated within the PS-b-PMMA lamellae. Furthermore, the nanoporous bicontinuous thin films were fabricated on the silicon substrates and the morphological behaviors were quantitatively investigated by grazing-incidence small-angle X-ray scattering (GISAXS) analysis.

Free-standing nanocomposite multilayers with various length scales, adjustable internal structures, and functionalities.

We introduce an innovative and robust method for the preparation of nanocomposite multilayers, which allows accurate control over the placement of functional groups as well as the composition and dimensions of individual layers/internal structure. By employing the photocross-linkable polystyrene (PS-N(3), M(n) = 28.0 kg/mol) with 10 wt % azide groups (-N(3)) for host polymer and/or the PS-N(3)-SH (M(n) = 6.5 kg/mol) with azide and thiol (-SH) groups for capping ligands of inorganic nanoparticles, nanocomposite multilayers were prepared by an efficient photocross-linking layer-by-layer process, without perturbing underlying layers and nanostructures. The thickness of individual layers could be controlled from a few to hundreds of nanometers producing highly ordered internal structure, and the resulting nanocomposite multilayers, consisting of polymer and inorganic nanoparticles (CdSe@ZnS, Au, and Pt), exhibit a variety of interesting physical properties. These include prolonged photoluminescent durability, facile color tuning, and the ability to prepare functional free-standing films that can have the one-dimensional photonic band gap and furthermore be patterned by photolithography. This robust and tailored method opens a new route for the design of functional film devices based on nanocomposite multilayers.