Young-Je Kwark

Soongsil University · Department of Organic Materials and Fiber Engineering

A porous nanofiber web with a hierarchical pore structure was formed by electrospinning and nonsolvent-induced phase separation (NIPS) processes. Phenyl silsesquiazane (PSSQZ) containing 20% high-molecular-weight poly(ethylene oxide) (PEO) was electrospun to form a nanofiber web, where a mixture of high volatility solvent and low volatility nonsolv...

A hierarchically porous SiCN monolith with aligned macropores was prepared using a branch‐structured polysilazane, silsesquiazane (SSQZ), as a precursor and polymer additive, through the freeze casting method. As polymer additives, polystyrene (PS) and poly(methyl methacrylate), which have different compatibilities with SSQZ, were used to confirm t...

We investigated the luminescent behavior of KBPO4 (KBPO4:Eu) nanocrystals (NC) doped with europium (Eu) ions, where B = Ca, Sr, and Ba. The NC samples were fabricated via the chemical method and annealed in different ambient environments for regulating the number of oxygen vacancies in the NCs. We observed that the as-synthesized KBPO4:Eu exhibited...

Polytetrafluoroethylene (PTFE) has high thermal stability and chemical resistance, and hence is gaining great attention in the industrial field of high-performance filters, membranes, and medical applications. However, since PTFE possesses a narrow gap between melting (330°C) and decomposition temperatures (350°C), the melt-spinning process that is...

A Co²⁺ adsorbent was prepared using electrospun porous polyacrylonitrile (PAN) nanofibers, featuring easy recovery for reuse compared with a nanoparticle-based adsorbent. As an efficient ligand for Co²⁺, ethylenediaminetetraacetic acid (EDTA) was introduced on the surface of porous PAN nanofibers with the aid of a branched polyethyleneimine (PEI) l...

Magnetoceramics composed of pure α-Fe crystals grown in an amorphous silicon carbonitride matrix were prepared using phenyl-silsesquiazane (PSSQZ) and iron oxide (Fe3O4) as precursors. Magnetoceramics with commercial polysilazane were also synthesized for comparison. The PSSQZ induced growth of only α-Fe crystals in the magnetoceramics because of t...

In this study, a conductive Si/C/N/Ni nanocomposite was prepared using phenyl-substituted polysilazane and nickelocene (NiCp2) as precursors. Ni-related nanoparticles were uniformly distributed throughout the Si/C/N/Ni nanocomposite without aggregation because of the large number of nitrogen atoms in the silsesquiazane used as a precursor of the ma...

To fabricate an efficient Cs ion adsorbent and prevent unexpected loss of Prussian blue (PB) colloidal particles during use, PB was immobilized on the surface of electrospun mesoporous silica nanofibers (MSFs) via a newly developed method of double exposure to Fe (III) ions. To introduce PB on MSFs, the MSFs were functionalized with ethylenediamine...

The Knoevenagel condensation was applied to the interfacial polymerization of difunctional aldehyde and trifunctional acetonitrile monomers for the first time. The polymerization was conducted at the interface between water containing a base and an organic phase containing the monomers at room temperature for periods ranging from a day to several w...

In this study, silver/polyimide (Ag/PI) composite films with enhanced heat dissipation properties were prepared. Ag was formed in situ by reducing AgNO 3 at various locations according to the reduction method. Two different types of soluble PIs capable of solution processing were used, namely Matrimid and hydroxy polyimide (HPI). Unlike Matrimid wi...

Inverse suspension polymerization method was applied to prepare poly(itaconic acid) based superabsorbent particles. The polymerization process was investigated to determine the influence of different parameters on the water absorption properties. It was found that processing parameters, such as oil/aqueous phase ratio, surfactant, stirring speed, a...

Polyimides (PIs) possess excellent thermal and mechanical properties, but their poor solubility in organic solvents restricts their utility. Numerous studies have focused on improving PI solubility by weakening inter-molecular interactions within the polymer. The polyimide composed of aromatic anhydride, 6,6′-(hexafluoroisopropylidene)dipthalic anh...

In this paper, we manufactured silsesquiaznae (SSQZ)-coated carbon nanotube (CNT) surface heating elements, which allowed stable heating at high temperatures. The prepared composite sheet was confirmed by FE-SEM that the SSQZ fully coated the surface of CNT sheet. Furthermore, it was also confirmed that the silicon carbonitride (SiCN) ceramic forme...

Porous polyacrylonitrile (P-PAN) nanofibers containing a conjugated microporous polymer (CMP) with photocatalytic ability were electrospun to obtain a reusable photocatalyst composite. P-PAN nanofiber was used as a robust supporting matrix for the CMP and could prevent undesirable CMP leakage during use. To provide porous nanofibers, poly (vinyl py...

The emission properties of the rare earth (RE) elements have been found to be sensitive to the local lattice environment around them, and could be employed for probing the local lattice environment. Because each constituent ion of a material should have its own particular structural environment, the emission profiles in RE elements depend strongly...

Hierarchically porous silicon carbonitride (SiCN) was prepared using the freeze casting method with silsesquiazane (SSQZ) as a precursor. As SSQZ possesses a highly branched structure, it can provide a higher cross-linking degree than linear polysilazane and thereby, improve the structural stability. The porous SiCN can be produced without collapsi...

Biomineralization of calcium carbonate has interesting characteristics of intricate morphology formation with controlled crystal polymorphs. In particular, modification of calcite morphology with diverse additives has been the focus of many biomimetic and bioinspired studies. The possible role of strontium ions in enhancing the morphology-modifying...

A series of linear aromatic copolyimides (Co-PIs) were synthesized by reacting 4,4′-biphthalic anhydride (BPA) with various molar contents of 2,2′-bis(trifluoromethyl)benzidine (TFB) and p-xylylenediamine (p-XDA) in N,N′-dimethylacetamide (DMAc). Co-PI films were fabricated by solution casting and thermal imidization with poly(amic acid) (PAA) on g...

A mixture of polysiloxane (PSO) and polysilazane (PSZ) was used to prepare a crosslinked organosilicon material for use as an LED encapsulant. The crosslinking was conducted by using two different chemistries: platinum-catalyzed hydrosilylation and peroxide-initiated radical reaction. Successful crosslinking was confirmed by FT-IR spectroscopy, whi...

Superabsorbent polymers of carboxymethyl cellulose-graft-itaconic acid were synthesized using potassium persulfate as a free radical initiator in the presence of N,N′-methylene bisacrylamide as a crosslinker using solution polymerization technique. The structures of the grafted copolymers were characterized by FT-IR spectroscopy and thermogravimetr...

Homogeneous polyimide (PI)/silica nanohybrid films were prepared using acetoxy group functionalized PI and silsesquiazane (SSQZ) as a silica precursor. During the heat treatment at 250 °C in a nitrogen atmosphere, the SSQZ was converted to silica. At the same time, the acetoxy groups of PI were converted into hydroxyl groups and formed covalent bon...

Spontaneously wrinkled films can be easily obtained from UV-crosslinkable liquid prepolymers under special UV-curing conditions. They vary wrinkle structures of the UV-cured films and, however, cannot be precisely controlled. Here, five different UV-crosslinkable prepolymers are synthesized to study the chemical structure effect of prepolymers on w...

In the present work, graft copolymers of acrylamide onto guar gum were synthesized by free radical polymerization using potassium bromate/thiourea redox initiating system. The guar gum and guar gum-g-polyacrylamide were characterized by infrared spectroscopy and thermogravimetric analysis. It was found that the guar gum-g-polyacrylamid was thermall...

We report a novel solvent-free and direct photo-patternable poly[(mercaptopropyl)methyl-siloxane] (PMMS) hybrid dielectric for flexible top-gate organic field-effect transistors (OFETs), utilizing a photo-activated thiol-ene reaction under UV irradiation of 254 nm to induce cross-linking, even in air and at low temperature. In particular, a solvent...

A series of well-defined hard-soft-hard triblock copolymers were synthesized by Ru-based atom transfer radical polymerization (ATRP) (MWD < 1.26) in order to examine their electromechanical properties under electric fields. The obtained methacrylate based triblock copolymers consisted of poly(dodecyl methacrylate) (PDMA) soft middle block segments...

We examined the deboronation reaction of 4-mercaptophenylboronic acid (4MPBA) via fructose and glucose on silver surfaces by means of surface-enhanced Raman scattering (SERS) at the excitation wavelengths of 488, 514, and 633 nm. The SERS spectra on silver nanoparticles clearly exhibited specific spectral signatures of thiophenol (TP) peaks, indica...

Artificial wrinkles have recently been in the spotlight due to their potential use in high-tech applications. A spontaneously wrinkled film can be fabricated from UV-crosslinkable liquid prepolymers. Here, we controlled the wrinkle formation by simply formulating two UV-crosslinkable liquid prepolymers, tetraethylene glycol bis(4-ethenyl-2,3,5,6-te...

The passivation layer, which is located between a pixel electrode and a data electrode, must provide sufficiently low parasitic capacitance and sufficient electrical insulation to reduce cross talk and signal distortion. The present demand for passivation materials for next-generation displays has created interest in substitutes with low dielectric...

Herein, we developed novel silicon-carbon-nitrogen (SiCN) composites synthesized by pyrolyzing silsesquiazane polymer as an anode material for rechargeable lithium-ion batteries. Among variable pyrolysis temperatures of 700 °C, 1000 °C and 1300 °C, the SiCN composites prepared at 1000 °C showed the highest capacity with outstanding battery cycle li...

Nano-scale drug delivery systems have undergone extensive development, and control of size and structure is critical for regulation of their biological responses and therapeutic efficacy. Amphiphilic polymers that form self-assembled structures in aqueous media have been investigated and used for the diagnosis and therapy of various diseases, inclu...

Special characteristics of wrinkles such as a scattering source and a high surface area are finding use in high-tech applications. UV-crosslinkable prepolymers are occasionally used for fabricating wrinkled films. Wavelength of the wrinkles formed from the prepolymers is several tens and hundreds of micrometers. Here, a UV-crosslinkable liquid prep...

The dispersion of calcium carbonate (CaCO3) in polypropylene (PP) and the effect of CaCO3 size on the crys-tallinity of PP were studied. Polymer composite usually suffers from the brittleness when reinforced with inorganic fillers. The problem is generally related to the size and dispersion of fillers. First, the dispersion was studied for the nano...

We investigated the temperature-dependent emission property of ferroelectric Pb(Zr,Ti)O3 (PZT) nanotubes with variation of the outer diameter from 60 nm to 420 nm at a fixed wall-thickness (25 nm). The PZT nanotubes were synthesized in the sol-gel template directed method with a spin-coating process. While the emission peak positions show a red-shi...

Densely structured polyhedral oligomeric silsesquioxane (POSS) was employed as an additive to enhance hardness of silicon-based hybrid gels for LED encapsulants. To improve the miscibility of POSS and polysiloxane resin, alkyl or oligosiloxane branches were introduced to POSS moiety. Platinum-catalyzed hydrosilylation reactions were used to attach...

Poly(ethylene oxide-b-acrylonitrile) (PEO-b-PAN) block copolymers were prepared as precursors to mesoporous carbons. Redox-initiated radical polymerization and controlled radical polymerization techniques, such as reversible addition-fragmentation chain transfer (RAFT) and activators regenerated by electron transfer atom-transfer radical polymeriza...

Chemotherapy is a widely adopted method for the treatment of cancer. However, its use is often limited due to side effects produced by anti-cancer drugs. Therefore, various drug carriers, including polymeric micelles, have been investigated to find a method to overcome this limitation. In this study, alginate-based, self-assembled polymeric micelle...

In organic field-effect transistors (OFETs), surface modification of the gate-dielectric is a critical technique for enhancing the electrical properties of the device. Here, we report a simple and versatile method for fabricating an ultrathin crosslinked interlayer (thickness ~3 nm) on an oxide gate dielectric by using polymeric silsesquiazane (SSQ...

In tissue engineering, the nanoscale topography of the substrate is important, because transplanted cells can recognize and respond to topographical patterns, allowing control of gene expression and tissue formation. In this study, we hypothesized that the height of cell-adhesive nanoposts could regulate cell phenotype. Nano-patterned surfaces were...

In our search for a new red phosphor, we investigated the photoluminescence from the high-K material SrHfO3 with co-doping of Eu3+ and Sm3+. We found that the red emission from co-doped SrHfO3 depended strongly on the doping concentrations of Eu3+ and Sm3+ and that the intensity was strongest for Eu3+ 1% (x = 0.01) and Sm3+ 1% (y = 0.01) co-doping....

Two different polysilanes, poly(methyl(phenyl)silane) (PMPS) and poly(methyl(phenyl)silane-co-methyl(vinyl)silane) (PMPS-co-PMVS), were synthesized as precursor polymers to ceramics as anodes in lithium ion batteries. Upon pyrolysis at 1000^{\circ}C, the polysilanes yielded ceramics with a Si content of 67-70%. The vinyl group containing PMPS-co-PM...

A high level of control over the photoinitiated RAFT polymerization of vinyl acetate (VAc) was achieved using a specifically designed xanthate, S-2-cyano-2-propyl-O-ethyl xanthate (CPEC), which acted as a radical source and a chain transfer agent simultaneously. Unlike other RAFT processes, the present system did not use any additional radical init...

A photoinitiated RAFT process in fluoroalcohols (FAs) was successfully applied to the preparation of poly(vinyl acetate) and its hydrolyzed polymer, poly(vinyl alcohol), permitting the simultaneous control over the molecular weight (MW) and tacticity. The polymerization reaction displayed living polymerization characteristics, evidenced with linear...

We investigated the structural and optical properties of Cu-poor CuGaSe2 (CGSe) films depending on the use of different substrates: indium-doped tin oxide (ITO) coated soda-lime glass (SLG) and fluorine-doped tin oxide (FTO) coated SLG as back contacts, widely used Mo-coated SLG, and pure SLG. The Cu-poor phase is chosen as a counterpart of Cu-poor...

Silsesquiazane (SSQZ), one of the branched forms of polysilazane, was blended with polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(iso-butyl methacrylate) (PBMA), and poly(vinyl acetate) (PVAc) to produce organic-inorganic hybrid materials. The polymers were selected to provide specific interaction, such as π-π interaction or hydrogen bond...

The surface nanotopography of polymer scaffolds is one of the most critical factors affecting cell phenotype and function in tissue engineering applications. We hypothesized that controlling the surface structure of polymer matrices on the nanometer size scale could be critical in the regulation of preosteoblast phenotypes. Nano-structured polymer...

We demonstrated multifunctional electrospun polyelectrolyte fabrics with switchable superhydrophobicity as well as oleophobicity. To produce this smart fabric, we used a strategy that combines electrospinning to fabricate nanofibrous templates with nanopores and a simple coating of the polyelectrolyte that can exchange counterions with various hydr...

Calcium carbonate () with 15~40 nm average diameter was compounded with polypropylene (PP) in a melted state to form composite materials. To enhance the dispersibility in PP, the surface of the was coated with hydrophobic stearic acid (SA). The SA-coated (SA-) showed hydrophobic nature, which resulted in rapid precipitation in water. When melt-comp...

A photoinitiation process was investigated to develop a rapid and well-controlled RAFT polymerization method applied to vinyl acetate (VAc) using methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as the RAFT agent and photoinitiator, respectively. MESA was selected as the photochemically inert...

The surface nanotopography of polymer substrates is a critical factor to regulate cellular behavior in tissue engineering approaches. In this study, nanopatterned surfaces were generated via self-assembly of polystyrene-b-poly(ethylene oxide)/dodecylbenzenesulfonic acid complex systems to control preosteoblast phenotype in vitro. Polystyrene domain...

We have demonstrated the preparation of interpenetrating polymer network (IPN) dielectrics for use in high-performance organic field-effect transistors by blending commercially available polymers (PMMA, PtBMA, and PS) with the crosslinkable polymeric silsesquiazane (SSQZ). This facile blending method is a powerful means of enhancing the electrical...

In this study, we prepared organic-inorganic hybrid nanoparticies with a core-shell structure using a surface-initiated polymerization technique. Initiators for the atom transfer radical polymerization were anchored onto the surface of silica nanoparticies, and from there N-isopropylacrylamide and methylene bisacrylamide were polymerized to form cr...

Polypropylene (PP)/multiwalled carbon nanotube (MWNT) composites were prepared with an environmentally benign processes. The surface functionalization of the MWNTs was performed with water as a solvent, and the functionalized MWNTs were mixed with PP to form composites with a melt process. The effects of the MWNTs on the mechanical and thermal prop...

Janus fabrics with superamphiphilicity were fabricated via electrospinning of polyacrylonitrile (PAN). PAN nanofibrous mats were formed on an aluminum foil substrate and then thermally treated to cause hydrolysis. An identical PAN solution was subsequently electrospun onto the hydrolyzed PAN layer, followed by peeling off of the bicomposite film fr...

Theoretical equation to predict kinetic absorption behaviors of swellable polymers was developed on the basis of Darcy’s law. The absorption pressure was derived on the model of binary interaction between polymer and solvent. The key variables considered in the equation were the absorption sites of polymer, the concentration of solvent, and the bin...

Poly(vinyl pyrrolidone) was used successfully to control the size and distribution of silver nanoparticles generated on inorganic silica nanofibers. The inorganic nanofibers were electrospun using sol-gel chemistry of silicates, and the diameter of the prepared nanofibers was unaffected by adding up to 7% of poly(vinyl pyrrolidone). The silver ions...

A new strategy using protection-deprotection chemistry was used to prepare branched polymers using the ATRP method only. Among the several monomers with different protecting groups, vinyl benzylt-butyloxy carbonate (VBt-BOC) and 4-methyl styrene (4-MeSt) could be polymerized successfully to form backbones using the ATRP method in a controlled fashi...

Nanofibers of phenylsilsesquiazanes (SSQZ), as a precursor of inorganic silicon nitride nanoweb, was prepared using the electrospinning process. The SSQZ was prepared by ammonolysis of phenyl trichlorosilane and condensation of the resulting aminosilanes. The molecular weight of resulting SSQZ increased with initial concentration of phenyl trichlor...

Silica nanofibers containing silver nanoparticles were successfully prepared using sol-gel chemistry and electro-spinning technique. Solution of tetraethly orthosilicate in ethanol containing silver nitrate was aged to have sufficient viscosity and electrospun to form nanofibers. Upon thermal treatment, the gelation reaction between silanols was co...

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends of various compositions were prepared by the solution-blending and melt-blending methods. The changes in miscibility and crystallization behaviors of the blends upon thermal treatment above the melting temperature of the blends at 280°C were investigated by using DSC, DM...

Pentamethylcyclopentadienyltitanium trichloride, bis(cyclopentadienyl)titanium dichloride (Cp2TiCl2), and bis(pentamethylcyclopentadienyl)titanium dichloride were used in the polymerization of styrene without the aid of Group I–III cocatalysts. The properties of the resulting polymer indicated that polymerization was more controlled than in thermal...

Performance requirements for extreme UV (EUV) resists will require the development of polymer platforms. A challenge in designing photoresists for EUV wavelengths is the selection of molecular structures that have minimal absorbance. For example, elements that are commonly used in photoresists at other wavelengths, such as oxygen and fluorine, are...

The opportunities posed by extreme ultraviolet (EUV) lithography are encouraging the development of new resist platforms. The absorbance characteristic of materials required for the EUV lithography demands the use of polymers containing highly transparent silicon atoms. At the same time, very low levels of outgassing of silicon containing fragments...

The uniqueness in extreme ultraviolet (EUV) Lithography is encouraging the development of new polymer platform as a resist material. The absorbance characteristic of materials at the EUV region demands the use of polymers containing highly transparent silicon atoms. Also very low level of outgassing is required due to the vacuum environment during...

The demands for high resolution and issues of line edge roughness require a reconsideration of current resist design strategies. In particular, EUV lithography will provide an opportunity to examine new resist concepts including new elemental compositions and low molar mass resists or molecular resists. In the former case, resist compositions incor...

Fluorinated polymers form an interesting class of materials with a wealth of unique properties including self-assembly, remarkably low surface energies, low absorbance to 157 nm UV light, and solubility in supercritical carbon dioxide. As a result many fluorinated polymers are of use in advanced technology applications. We review some of our work o...

To fulfill industry requirements for EUV resists, the development of entirely new polymer platforms is needed. In order to address transparency issues, we have been studying low absorbance materials, specifically silicon based resist platforms. In this approach, we have synthesized and studied resist materials based on polysilanes, polycarbosilane,...

The poly(ethylacrylate) (PEA) homopolymer and poly(ethylacrylate-co-sodium acrylate) ionomer that contain 8.4 mol % ionic groups (PEANa-8.4) were studied by 13C using cross polarization and magic angle spinning nuclear magnetic resonance (CP/MAS NMR). The 13C spin-lattice relaxation times in a rotating frame, T1ρ, were measured as functions of the...

Performance requirements for EUV resists may require the development of entirely new polymer platforms. In the first approach, we have synthesized norbornene-based copolymers using ring-opening metathesis polymerization (ROMP). Silicon containing norbornenes were synthesized and copolymerized with a series of monomers having acid sensitive and pola...

Several strategies were employed to improve the transparency and etch resistance of the acrylate-based 157 nm photoresists. (1) α-Fluorinated acrylates were synthesized and polymerized using radical initiation. The homopolymer of 2-[4-(2-hydroxy-hexafluoroisopropyl)cyclohexane]hexafluoro isopropyl-α-monofluoroacrylate (FA) showed high transparency...

Hexafluoroisopropyl alcohol-functionalized acrylate monomers and their (co)polymers were prepared as photoresist platforms for 157 nm imaging. In order to balance transparency with other desirable traits such as etch resistance, we developed several copolymer systems. One is using 2-methyl adamantyl methacrylate as a comonomer, and the copolymer sy...

2-[4-(2-hydroxyhexafluoro isopropyl)cyclohexane]hexafluoroisopropyl acrylate (AF) was prepared as a key monomer for 157 nm photoresist platforms. In order to balance transparency with other desirable traits such as etch resistance, new strategies for high resolution photoresists were developed and are discussed. (1) The alpha-trifluoromethyl group...

Atom transfer radical polymerization involves reversible one-electron oxidation of transition metal complexes accompanied by atom transfer. The metal catalyst should be able to undergo reversible 1-electron chemistry without degradative side reactions. In the context of polymer synthesis, several concerns arise. Such concerns are addressed through...

A new approach to determine kinetic parameters of polymerization of styrene based on a nonlinear regression was reported. Because the polymerization itself is too complex to describe in terms of the number of necessary differential equations, small molecular atom transfer radical addition (ATRA) reactions were used as model reactions. Several side...

Vinyl acetate (VAc) and vinyl pivalate (VPi) were homopolymerized and copolymerized by low-temperature redox emulsion polymerization using a manganese chelate as initiator. The polymerization kinetics in these systems were investigated by a mathematical model and estimating the respective kinetic parameters. Among the parameters, the radical entry...