Kyung Youl Baek

Molecular layer-by-layer assembled thin-film composite membranes for water desalination

Molecular layer-by-layer (mLbL) assembled thin-film composite membranes fabricated by alternating deposition of reactive monomers on porous supports exhibit both improved salt rejection and enhanced water flux compared to traditional reverse osmosis membranes prepared by interfacial polymerization. Additionally, the well-controlled structures achieved by mLbL deposition further lead to improved antifouling performance.

High photo- and electroluminescence efficiencies of ladder-like structured polysilsesquioxane with carbazole groups

Ladder-like structured polysilsesquioxane with carbazole groups showed unexpected high photo- and electroluminescence efficiencies both in solution and solid states due to its rigid silicone ladder structures, which efficiently isolated the carbazole groups and thus suppressed their excimer formations by inter- and intramolecules.

Tailor-Made Polyamide Membranes for Water Desalination

Independent control of the extrinsic and intrinsic properties of the polyamide (PA) selective layer is essential for designing thin-film composite (TFC) membranes with performance characteristics required for water purification applications besides seawater desalination. Current commercial TFC membranes fabricated via the well-established interfacial polymerization (IP) approach yield materials that are far from ideal because their layer thickness, surface roughness, polymer chemistry, and network structure cannot be separately tailored. In this work, tailor-made PA-based desalination membranes based on molecular layer-by-layer (mLbL) assembly are presented. The mLbL technique enables the construction of an ultrathin and highly cross-linked PA selective layer in a precisely and independently controlled manner. The mLbL-assembled TFC membranes exhibit significant enhancements in performance compared to their IP-assembled counterparts. A maximum sodium chloride rejection of 98.2% is achieved along with over 2.5 times higher water flux than the IP-assembled counterpart. More importantly, this work demonstrates the broad applicability of mLbL in fabricating a variety of PA-based TFC membranes with nanoscale control of the selective layer thickness and roughness independent of the specific polyamide chemistry.

Novel Polymer Nanowire Crystals of Diketopyrrolopyrrole‐Based Copolymer with Excellent Charge Transport Properties

The first demonstration of polymer nanowire (PNW) crystals based on a diketopyrrolopyrrole-based copolymer (i.e., PDTTDPP), and their application to field-effect transistors (FETs) is reported. Remarkably, transmission electron microscopy and selected area electron diffraction analyses of the PNW reveal its single-crystalline (SC) nature. FETs fabricated of a SC PNW exhibit a maximal charge carrier mobility of ≈7.00 cm(2) V(-1) s(-1) , which is almost one order of magnitude higher than that of the thin-film transistors made of the same polymer (PDTTDPP).

Fouling-Tolerant Nanofibrous Polymer Membranes for Water Treatment

Nafion/polyvinylidene fluoride (PVDF) nanofibrous membranes with electrostatically negative charges on the fiber surface were fabricated via electrospinning with superior water permeability and antifouling behaviors in comparison with the conventional microfiltration membranes. The fiber diameter and the resultant pore size in the nanofibrous membranes were easily controlled through tailoring the properties of the electrospinning solutions. The electrospun Nafion/PVDF nanofibrous membranes revealed high porosities (>80%) and high densities of sulfonate groups on the membrane surface, leading to praiseworthy water permeability. Unexpectedly, the water permeability was observed as proportional to the fiber diameter and pore size in the membrane. The presence of sulfonate groups on the membrane improved the antifouling performance against negatively charged oily foulants.

Rational design of multiamphiphilic polymer compatibilizers: Versatile solubility and hybridization of noncovalently functionalized CNT nanocomposites

The design of amphiphilic polymer compatibilizers for solubility manipulation of CNT composites was systematically generalized in this study. Structurally tailored multiamphiphilic compatibilizer were designed and synthesized by applying simple, high-yield reactions. This multiamphiphilic compatibilizer was applied for noncovalent functionalization of CNTs as well as provided CNTs with outstanding dispersion stability, manipulation of solubility, and hybridization with Ag nanoparticles (NPs). With regard to the dispersion properties, superior records in maximum concentration (2.88-3.10 mg/mL in chloroform), and mass ratio of the compatibilizer for good CNT dispersion (36 wt %) were achieved by MWCNTs functionalized with a multiamphiphilic block copolymer compatibilizer. In particular, the solubility limitations of MWCNT dispersion in solvents ranging from toluene (nonpolar) to aqueous solution (polar) are surprisingly resolved by introducing this multiamphiphilic polymer compatibilizer. Furthermore, this polymer compatibilizer allowed the synthesis of the hybrid CNT nanocomposites with Ag nanoparticles by an in situ nucleation process. As such, the multiamphiphilic compatibilizer candidate as a new concept for the noncovalent functionalization of CNTs can extend their use for a wide range of applications.

Ionic block copolymer doped reduced graphene oxide supports with ultra-fine Pd nanoparticles: strategic realization of ultra-accelerated nanocatalysis

We synthesized an ultra-fine Pd nanocatalyst supported by ionic block copolymer doped reduced graphene oxide (Pd-PIBrGO) for ultra-accelerated nanocatalysis. This hybrid catalyst exhibited exceptionally advanced catalytic performance for the reduction of methylene blue using miniscule quantities of Pd-PIBrGO due to facilitated diffusion of reagents, resulting in full reduction within a few seconds and showing a 280-fold increase of the rate constant over Pd-rGO without ionic block copolymers.

Cationically photopolymerizable epoxy-functionalized thermoplastic polysilsesquioxanes: synthesis and properties

A series of epoxy-functionalized inorganic–organic hybrid ladder-like structured polysilsesquioxanes were synthesized in one-batch via a base-catalyzed co-solvent system. Two types of epoxy functionalities were examined: aliphatic and cycloaliphatic. Obtained polymeric epoxy-functionalized ladder-like polysilsesquioxanes were cationically photopolymerized under UV irradiation over glass and plastic substrates. Obtained cross-linked films were examined as hardcoating materials as their thermal, optical, mechanical, and barrier properties were studied. These materials showed superior thermal properties (Td > 400 °C), high optical transparency (>95%), high pencil hardness (4H–9H), low dielectric constant (3.0–3.6), and good barrier properties (WVTR < 101 g m−2 day−1, OTR < 102 g m−2 day−1).

Molybdenum-Doped PdPt@Pt Core-Shell Octahedra Supported by Ionic Block Copolymer-Functionalized Graphene as a Highly Active and Durable Oxygen Reduction Electrocatalyst.

Development of highly active and durable electrocatalysts that can effectively electrocatalyze oxygen reduction reactions (ORR) still remains one important challenge for high-performance electrochemical conversion and storage applications such as fuel cells and metal-air batteries. Herein, we propose the combination of molybdenum-doped PdPt@Pt core-shell octahedra and the pyrene-functionalized poly(dimethylaminoethyl methacrylate)-b-poly[(ethylene glycol) methyl ether methacrylate] ionic block copolymer-functionalized reduced graphene oxide (Mo-PdPt@Pt/IG) to effectively augment the interfacial cohesion of both components using a tunable ex situ mixing strategy. The rationally designed Mo-PdPt@Pt core-shell octahedra have unique compositional benefits, including segregation of Mo atoms on the vertexes and edges of the octahedron and 2-3 shell layers of Pt atoms on a PdPt alloy core, which can provide highly active sites to the catalyst for ORR along with enhanced electrochemical stability. In addition, the ionic block copolymer functionalized graphene can facilitate intermolecular charge transfer and good stability of metal NPs, which arises from the ionic block copolymer interfacial layer. When the beneficial features of the Mo-PdPt@Pt and IG are combined, the Mo-PdPt@Pt/IG exhibits substantially enhanced activity and durability for ORR relative to those of commercial Pt/C. Notably, the Mo-PdPt@Pt/IG shows mass activity 31-fold higher than that of Pt/C and substantially maintains high activities after 10 000 cycles of intensive durability testing. The current study highlights the crucial strategies in designing the highly active and durable Pt-based octahedra and effective combination with functional graphene supports toward the synergetic effects on ORR.

A facile synthetic route for highly durable mesoporous platinum thin film electrocatalysts based on graphene: morphological and support effects on the oxygen reduction reaction

Porous-structured noble metal electrocatalysts offer activity and durability benefits based on a high surface area and interconnected nanostructure, respectively. However, conventional technical methods used for synthesizing a porous structure are still difficult as well as resulting in defects in the structure. Here we report a facile route for the synthesis of uniform, large-area mesoporous platinum thin films based on ionic polymer doped graphene, which exhibit substantially enhanced activity and durability for oxygen reduction relative to commercial Pt/C. Notably, a remarkable durability (≥95% retention of electrochemical activities after 30 000 cycles of intensive accelerated durability tests) is acquired which is ascribed to the synergistic effects derived from the interconnected Pt structure (morphology) and ionic polymer-doped graphene (support). The suggested robust concept for a controlled mesoporous-structured platinum thin film on graphene could be a great breakthrough for obtaining a highly durable electrocatalyst.