Kwang-Suk Jang

Enhanced performance of solution-processed organic thin-film transistors with a low-temperature-annealed alumina interlayer between the polyimide gate insulator and the semiconductor.

We studied a low-temperature-annealed sol-gel-derived alumina interlayer between the organic semiconductor and the organic gate insulator for high-performance organic thin-film transistors. The alumina interlayer was deposited on the polyimide gate insulator by a simple spin-coating and 200 °C-annealing process. The leakage current density decreased by the interlayer deposition: at 1 MV/cm, the leakage current densities of the polyimide and the alumina/polyimide gate insulators were 7.64 × 10(-7) and 3.01 × 10(-9) A/cm(2), respectively. For the first time, enhancement of the organic thin-film transistor performance by introduction of an inorganic interlayer between the organic semiconductor and the organic gate insulator was demonstrated: by introducing the interlayer, the field-effect mobility of the solution-processed organic thin-film transistor increased from 0.35 ± 0.15 to 1.35 ± 0.28 cm(2)/V·s. Our results suggest that inorganic interlayer deposition could be a simple and efficient surface treatment of organic gate insulators for enhancing the performance of solution-processed organic thin-film transistors.

Improving the thermoelectric power factor of CNT/PEDOT:PSS nanocomposite films by ethylene glycol treatment

This study investigates a post treatment method for improving the thermoelectric properties of carbon nanotube (CNT)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) nanocomposite films. Ethylene glycol (EG) treatment is performed by immersing the as-prepared CNT/PEDOT:PSS nanocomposite films in EG for 1 h followed by annealing at 140 °C for 10 min. Non-complexed PSS chains could be effectively removed using the EG treatment, resulting in a decrease in inter-bundle distances in the nanocomposite films. This drastically increases the electrical conductivity of the PEDOT:PSS matrix. EG-treated nanocomposite films with 20 wt% CNTs exhibited the highest power factor of 151 ± 34 μW m−1 K−2 among all the prepared samples. Our results indicate that the EG treatment is a promising method for fabricating cost-effective, high-performance thermoelectric CNT/PEDOT:PSS nanocomposite films. We fabricated an organic thermoelectric generator using EG-treated CNT/PEDOT:PSS nanocomposite patterns and evaluated its electric power generation capabilities.

Ultrasmall polymersomes of poly-α,β-(N-2-hydroxyethyl L-aspartamide)-graft-poly(L-lactic acid) copolymers as a potential drug carrier

Ultrasmall polymersomes of poly-α,β-(N-2-hydroxyethyl L-aspartamide)-graft-poly(L-lactic acid), 40–45 nm in diameter, were prepared based on a well-defined graft copolymer architecture and well-managed self-assembly process. The ultrasmall polymersomes are a proposed drug delivery platform based on their suitable size, narrow size distribution, uniform morphology, and high thermodynamic stability, which satisfy prerequisites for systemic drug delivery carriers. The functionality and versatility of this system as a potential general drug delivery platform are supported by its biodegradability, favorable modifiable chemical formula, and flexible polymersome size that could be tuned to a nanoscopic range by manipulating the thermodynamic balance of the self-assembly process.

Synthesis and characterization of thermally curable 4-(1,2,2-trifluorovinyloxy)benzoyl substituted poly(4-vinylphenol) for gate insulator in thin film transistor

ABSTRACT We have synthesized a thermally curable polymeric gate insulator (TFVOB-PVP) through the modification of the well-known poly(4-vinylphenol) (PVP) polymer using a 4-(1,2,2-trifluorovinyloxy) benzoyl (TFVOB) chloride. The thermal cross-linking of TFVOB-PVP was conducted and produced the cross-linked TFVOB-PVP with the perfluorocyclobutane (PFCB) structure. The PFCB structure was formed by the radical mediated thermal cycloaddition of trifluorovinyl ether group of TFVOB. The cross-linked TFVOB-PVP showed good thermal stability up to 423°C with only 5% weight loss and excellent chemical resistance to common organic solvents. The pentacene thin-film transistor (TFT) with the cross-linked TFVOB-PVP as a gate dielectric exhibited a field effect mobility of 0.14 cm2/Vs with almost no hysteresis during the TFT operation.

Diverse morphologies of self-aggregates from dodecyl chain grafted poly(2-hydroxyethyl aspartamide) in aqueous solution

A series of amphiphilic graft copolymers, poly(2-hydroxyethyl aspartamide) grafted with dodecyl chains with different degree of substitution (DS), were synthesized and their self-aggregates showing various morphologies in aqueous media were prepared by direct dissolution method. Spherical micelles, wormlike micelles, tubular networks, and vesicles observed by TEM were found to be a function of DS of the hydrophobic dodecyl chain, and those self-assembled nanostructures can be explained in terms of interfacial energy and packing parameter. To our knowledge, this is the first report of diverse morphologies for a comb-like amphiphilic graft copolymer system. Our system suggests very attractive advantages for biomedical applications and for mass production of aggregates by direct dissolution into water without an organic solvent.

Biolabeling and Binding Evaluation of Amphiphilic Nanocrystallopolymers

Surfactant-like inorganic-organic hybrid molecules named as nanocrystallopolymers were designed by conjugation of the hydrophilic synthetic poly(amino acid), poly-ź,β-(N-(2-hydroxyethyl)l-aspartamide), with hydrophobic inorganic nanoparticles. In aqueous media, amphiphilic nanocrystallopolymers form self-aggregates with unique morphologies. Here, a simple biolabeling method of nanocrystallopolymers was developed. Biotin was selected as a model biomolecule. The specific binding of biotin-labeled nanocrystallopolymers to the targeted surface was evaluated with a surface plasmon resonance sensor.

Synthesis and thermal transition behaviour of new reactive mesogens with propiolate (-C≡C-COO-) linkages

New diacrylate reactive mesogens (Ph1 and Fl1) with propiolate (-C≡C-COO-) linkages between the aromatic rings have been synthesised. Either 2-methylphenyl-1,4-diol (Ph) or 9,9-diethylfluorene-2,7-diol (Fl) was used as a central core unit. The mesomorphic properties were then compared with those of the homologues Ph2 and Fl2, which contain ester (-COO-) linkages. The new compounds Ph1 and Fl1 exhibited an increased nematic mesophase window that was probably caused by the additional triple bond present in the propiolate (-C≡C-COO-). Interestingly, the homologues Fl1 and Fl2, which were based on a 9,9-diethylfluorene-2,7-diol (Fl) core unit, showed a polymorphism. Furthermore, double clearing behaviour was observed by polarised optical microscopy for the compound Fl2, which to the best of our knowledge is the first example of such behaviour in reactive mesogens.