Misang Yoo

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.

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.

A Strategy to Decorate the Surface of NPs and Control their Locations within Block Copolymer Templates

Polymer nanocomposites consisting of polymers and inorganic nanoparticles (NPs) have attracted many attentions due to their promising potentialsof diverse applications such as solar cell, sensors, catalysts, ferroelectric devices, etc. To impart sufficient stability of NPs and integrate NPs into polymer matrix, it is a prerequisite that the surface of the NPs is properly treated with various ligands having desired properties. Up to date, a number of strategies to synthesize the appropriate gold nanoparticles (Au NPs) have been reported. The most popular method that has been for a long time to prepare Au NPsis to use citrate reduction of HAuCl4 in water, which was introduced by Turkevitch (Turkevich et al., 1951). And this method was developed by Frens to obtain controlled size of Au NPs from 10 to 100 nm, via varying the concentration ratio between HAuCl4 and sodium citrate (Frens, 1973). In organic solvent, the so called “two-phase method” developed by Brust et al. has a considerable impact in this field until today due to the facile synthesis of stable Au NPsthat are protected by alkanethiols with controlled size and monodispersity (Brust et al., 1994). Later, they also introduced the “one-phase method” in methanol (Brust et al., 1995) and Yee et al. have expanded this method to various metal NPs such as gold, palladium and iridium in tetrahydrofuran (Yee et al., 1999). Furthermore, Hostetler et al. demonstrated that the functionality of monolayer protected NPs can be further enhanced via ligand exchange method (Hostetler et al., 1999). Recently, the inorganic NPs which is surface modified with polymeric ligands instead of the small surfactant molecules, such as alkanethiols or citrate, have attracted great interest as they can provide not only the improved stability but also various functionalities, unique structure and characteristics, and compatibility with other matrices. As a versatile approach for the surface modification of NPs, it has been shown that various polymers can be grafted onto the NP surface via “grafting-from”, “grafting-to”, “ligand exchange” or “templating” methods. In the “grafting-from” method, polymers are usually grown from the NP surfacesvia living-free radical polymerization, which are modified with the initiators. In contrast, when the end-functionalized polymers are synthesized, such as thiol-terminated