Chang Y. Ryu

Solubility-driven thin film structures of regioregular poly(3-hexyl thiophene) using volatile solvents

Using atomic force microscopy and grazing-incidence x-ray diffraction, the authors found that the use of volatile CH2Cl2 not only offers an advantage in minimizing regioregular poly(3-hexyl thiophene) (RR P3HT) film deposition time, but also directs the desirable parallel orientation of π-π stacking planes of RR P3HT with respect to solid substrates, for both spin and drop castings. The substrate temperature effects have been investigated to support claims that the substrate-induced crystallization of RR P3HT preseeds the parallel oriented crystals prior to spin casting, when the warm CH2Cl2 solution is loaded on a “cold” substrate held at room temperature.

Density control of single-walled carbon nanotubes using patterned iron nanoparticle catalysts derived from phase-separated thin films of a polyferrocene block copolymer

Single-walled carbon nanotube (SWNT) density and bundle size has been controlled by a simple one step CVD growth process using a polyferrocenylsilane block copolymer as the pre-organized catalyst source.

Parallel arrays of individually addressable single-walled carbon nanotube field-effect transistors

High-throughput field-effect transistors (FETs) containing over 300 disentangled, high-purity chemical-vapor-deposition-grown single-walled carbon nanotube (SWNT) channels have been fabricated in a three-step process that creates more than 160 individually addressable devices on a single silicon chip. This scheme gives a 96% device yield with output currents averaging 5.4mA and reaching up to 17mA at a 300mV bias. Entirely semiconducting FETs are easily realized by a high current selective destruction of metallic tubes. The excellent dispersity and nearly-defect-free quality of the SWNT channels make these devices also useful for nanoscale chemical and biological sensor applications.

Thermal property of regioregular poly(3-hexylthiophene)/nanotube composites using modified single-walled carbon nanotubes via ion irradiation

The effects of radiation-induced modifications on the thermal stability and phase transition behaviour of composites made of 1% pristine or ion irradiated single-walled carbon nanotubes (SWNTs) and poly(3-hexylthiophene) (P3HT) are reported. Thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), Raman spectroscopy and electron spin resonance (ESR) were used to investigate the radiation-induced functionalization of carbon nanotubes and to assess the effect of ionizing radiation on the adhesion between macromolecular polymer and carbon nanotubes. Irradiation was used to introduce defects in a controlled way solely within pristine nanotubes before composite synthesis. The addition of irradiated SWNTs to a polymer matrix was found to enhance thermo-oxidative stability and phase transition behaviour. Further, ESR studies demonstrate the electronic interaction through charge transfer between filler and matrix. These results could have immense applications in nanotube composite processing. Based on the experimental data, a model for the interaction between polymeric chains and carbon nanotubes is proposed.

A novel pathogen detection system based on high‐resolution CE‐SSCP using a triblock copolymer matrix

Although CE-SSCP analysis combined with 16S ribosomal RNA gene-specific PCR has enormous potential as a simple and versatile pathogen detection technique, low resolution of CE-SSCP causes the limited application. Among the experimental conditions affecting the resolution, the polymer matrix is considered to be most critical to improve the resolution of CE-SSCP analysis. However, due to the peak broadening caused by the interaction between hydrophobic moiety of polymer matrices and DNA, conventional polymer matrices are not ideal for CE-SSCP analysis. A poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) (PEO-PPO-PEO) triblock copolymer, with dynamic coating ability and a propensity to form micelles to minimize exposure of hydrophobic PPO block to DNA, can be an alternative matrix. In this study, we examined the resolution of CE-SSCP analysis using the PEO-PPO-PEO triblock copolymer as the polymer matrix and four same-sized DNA fragments of similar sequence content. Among 48 commercially available PEO-PPO-PEO triblock copolymers, three were selected due to their transparency in the operable range of viscosity and PEO(137)PPO(43)PEO(137) exhibited the most effective separation. Significant improvement in resolution allowed discrimination of the similar sequences, thus greatly facilitated CE-SSCP analysis compared to the conventional polymer matrix. The results indicate that PEO-PPO-PEO triblock copolymer may serve as an ideal matrix for high-resolution CE-SSCP analysis.

Stability of ion implanted single-walled carbon nanotubes: Thermogravimetric and Raman analysis

In this work, the effect of different ions (hydrogen, helium, and neon) implanted on single-walled carbon nanotube (SWNT) is being analyzed using thermogravimetric analysis (TGA), Raman scattering, and x-ray photoelectron spectroscopy (XPS). The TGA result shows that the temperature for maximum decomposition rate (Tmax) increases at relatively low doses, i.e., by about 30°C after hydrogen ion implantation (at the ion dose of 1015cm−2), 17°C after helium ion implantation (at the ion dose of 1013cm−2), and contributes no significant enhancement after neon implantation for all doses. The increase of Tmax indicates that small mass ion can be utilized to improve the thermal-oxidative stability of SWNTs. Raman scattering and XPS were used to monitor the lattice damage from ion implantation and chemical bonding states of the materials. The results indicated the material rigidity for low doses of hydrogen and helium, while the application of higher doses of neon caused the material to transform towards amorphous ...

Discriminating Among Co-monomer Sequence Distributions in Random Copolymers Using Interaction Chromatography

Interaction chromatography has been employed to validate that adsorption of poly[styrene-co-(4-bromostyrene)] (PBr(x) S) random copolymers, where x denotes the mole fraction of 4-bromostyrene (4-BrS) in PBr(x) S in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co-monomer sequence distribution in PBr(x) S.

Micellar ordered structure effects on high-resolution CE-SSCP using Pluronic triblock copolymer blends

Pluronic F108 block copolymers have shown a great promise to achieve the desirable high resolution in the conformation‐sensitive separation of ssDNA using CE‐SSCP. However, fundamental understanding of the structures and properties of Pluronic matrix affecting the resolution is still limited. Unlike conventional gel‐forming homopolymers, Pluronic F108 block copolymers are amphiphilic macromolecules consisting of poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide) triblock copolymers, which are capable of forming a highly ordered micellar structure in aqueous solution. In this study, we have performed a series of experiments by blending different types of Pluronic polymers to control the formation of micelles and to study the correlation between separation and rheological characteristics of Pluronic gels affecting the resolution of CE‐SSCP. Our experiments have been specifically designed to elucidate how the micellar structure affects the resolution of CE‐SSCP upon altering the size uniformity and constituent homogeneity of the micelles. Our results suggest that uniformly sized micelle packing is the primary structural feature of Pluronic gel matrix for the high‐resolution separation, while the size and constituent of the micelle themselves need to be considered as secondary factors.

Micellar packing of pluronic block copolymer solutions: Polymeric impurity effects

AbstractSmall angle X-ray scattering (SAXS), dynamic light scattering (DLS), and high performance liquid chromatography (HPLC) experiments are performed to support that the inter-micellar distance of Pluronic cubic structures in aqueous solutions is governed by the poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblock copolymer concentration (not the overall polymer concentration) in the solutions. The “as-received (AR)” and “purified (Pure)” F108 solutions show a separate concentration dependence of body-centered cubic (BCC) lattice spacing, when the overall polymer concentration is used as a micellar packing parameter in aqueous solution. When the 22 wt% of non-micellizable polymeric impurities in the AR Pluronic F108 is taken into account, however, a universal concentration dependence of the BCC lattice spacing is observed, unifying results from both AR and Pure F108 solutions. When the PEO-PPO-PEO triblock copolymer concentration from the HPLC analysis is employed as an effective polymer concentration parameter, the universal relationship is observed to provide strong evidence that the polymeric impurities in AR F108 locate themselves in the less dense parts of the interstitial regions on the BCC lattice points, where were occupied by the triblock copolymer micelles. Although the polymeric impurities in AR F108 do not affect the actual triblock concentration dependence of the lattice spacing, they do shift the onset concentration of BCC micellar ordering. In the Pure F108, the onset of BCC packing occurs at the point where the nearest-neighbor radius (Rnn) in the BCC lattice is approximately equal to the hydrodynamic radius (Rh), indicating that lattice formation begins upon “hydrodynamic contact” between micelles. In the AR F108, the onset of packing occurs when Rnn/Rh is approximately 0.9, indicating that, in the presence of the polymeric impurities, micelles must be forced together beyond the point of hydrodynamic contact for the BCC packing.

High χ block copolymers based on chemical modification of poly(t-butyl acrylate) containing block copolymers

We report the synthesis and characterization of novel block copolymer (BCP) materials for the directed self-assembly (DSA) nanolithography applications. Specifically, the poly(t-butyl acrylate) (PtBA) block in the styrenic block copolymers have been chemically modified to a fluorinated block for the enhancement of the BCP χ-parameters. dPSb- PtBA had been first synthesized by anionic polymerization to prepare a well-defined BCP precursor with narrow polydispersity for the fluorination of PtBA block. Then, the precursor BCP was chemically modified by transalcoholysis of the PtBA-block with 2,2,2-trifluoroethanol. This strategy offers the advantage of flexibility and controllability to tailor the χ-parameter, while maintaining the narrow molecular weight distribution of the BCP materials for the advanced lithography applications. The transmission electron microscopy/small angle x-ray scattering (TEM/SAXS) characterization results of the modified BCP consisting of poly(fluoroalkylate) and PS supported the development of highly ordered lamellar domains in bulk.