Gil Sun Lee

Immobilization of poly(ethylene glycol) or its sulfonate onto polymer surfaces by ozone oxidation

A novel surface modification method has been developed to improve biocompatibility of polymeric biomaterials. This approach involves ozonation and then followed by graft polymerization with acrylates containing PEG, sulfonated PEG or by coupling of PEG derivatives. All the reactions were confirmed by ATR FT-IR and ESCA. The degree of ozonation measured by the iodide method was dependent on the ozone permeability of the polymers used. Surface hydrophilicity was investigated by measuring the contact angles. Ozonation itself yielded a slight increase in hydrophilicity and a decrease in platelet adhesion, but PEG immobilization showed a significant effect on surface hydrophilicity and platelet adhesion to confirm well-known PEGs passivity which minimize the adhesion of blood components on polymer surfaces. Both graft polymerization and coupling were effective for PU. In contrast, only grafting gave enough yields for PMMA and silicone. Platelet adhesion results demonstrated that all PEG modified surfaces adsorbed lower platelet adhesion than untreated or ozonated ones. Polymers coupled with sulfonated PEG exhibited the lowest platelet adhesion when compared with control and PEG coupled ones by virtue of the synergistic effect of non-adhesive PEG and negatively charged SO3 groups. This PEG or sulfonated PEG immobilization technology using ozonation is relatively simple for introducing uniform surface modification and therefore very useful for practical application of blood contacting medical devices.

Effect of phospholipid insertion on arrayed polydiacetylene biosensors

Micro-arrayed polydiacetylene (PDA) vesicles mixed with phospholipids on glass slides were prepared for label-free detection of Escherichia coli. When E. coli bound to its antibodies chemically attached to polydiacetylene, the fluorescence of the vesicles was dramatically increased. The insertion of dimyristoyl phosphatidylcholine (DMPC) in the vesicles drastically reduced the response time for the fluorescence changes. Vesicles with 20-30% DMPC provided optimal results for bacterial detection. Fourier transform infrared (FTIR) spectra analysis suggested that DMPC insertion decreased the strength of hydrogen bonding among the amide and carboxylic acid groups of the polydiacetylene vesicles. Reduced bonding strength resulted in less rigid structure of the polydiacetylene polymer, allowing more rapid detection upon molecular recognition.

Simple detection of food spoilage using polydiacetylene/poly(vinyl alcohol) hybrid films

Polydiacetylene (PDA)/poly (vinyl alcohol) (PVA) hybrid films are investigated for detection of ammonia gas generated by the food spoilage process. The films were obtained by mixing solutions containing diacetylene vesicles and aqueous PVA, and then drying. The films, which consist of carboxylic-acid-terminated PDA, showed a blue-to-red color transition upon reaction with ammonia gas. Through Fourier transform infrared (FTIR) analysis, we found that the observed color transition resulted from an ionic interaction between the carboxyl group of PDA and ammonia gas. In addition, patterned films were fabricated by selective UV irradiation through a photomask. Finally, the PDA/PVA hybrid films were found to show a color transition after reaction with real proteinic food at 25 °C. These results verify that the PDA/PVA hybrid films can be used for easier and more convenient real- time detection of food spoilage by the naked eye.

Rheology and curing characteristics of dual-curable clearcoats with hydroxyl functionalized urethane methacrylate oligomer: Effect of blocked isocyanate thermal crosslinkers

Rheological and mechanical properties of dual-curable automotive clearcoats containing different blocked isocyanate thermal crosslinkers (HDI, IPDI, and SMBI) have been compared by changing dual-curing sequences, i.e., UV-thermal dual curing and thermal-UV dual curing. Real-time elastic modulus data of clearcoats measured during several curing procedures have been correlated with the formation of crosslinked networks inside clearcoats. Clearcoat with SMBI shows increased modulus data due to the more reactive nature of functional groups in SMBI. Difference of rheological data of clearcoats under different curing temperatures during dual-curing sequences has been interpreted with the transition of chemical reactions inside clearcoats with different chemical structured crosslinkers. It turns out that scratch properties of cured clearcoats are also affected by the dual-curing sequence.

SELECTIVITY OF HEAVY METAL IONS AT ACIDIC SUPRAMOLECULAR SURFACES

Langmuir monolayers containing surface carboxylic acid head groups were examined in order to characterize their selectivity to metal ion adsorption. Experimental data of ion adsorption obtained by surface isotherms and FTIR spectroscopy were analyzed using a thermodynamic-and-electrochemical model. Among bivalent ions examined (Cr2+, Pb2+, Cu2+, Cd2+, Zn2+, Ca2+, Ni2+, and Ba2+), Langmuir monolayers showed the highest selectivity to chromium ions. In addition, it was found that adsorption constants of the surface ions are quite different from binding constants of the bulk ions. The results show important implications to sensing and separating metal ions by the use of acidic supramolecular materials.

Composition-dependent thermochromatic reversibility of polymerized diacetylene-xylenediamine complex films

Abstract

Photoluminescence Enhancement of Poly(3-methylthiophene) Nanowires upon Length Variable DNA Hybridization

The use of low-dimensional inorganic or organic nanomaterials has advantages for DNA and protein recognition due to their sensitivity, accuracy, and physical size matching. In this research, poly(3-methylthiophene) (P3MT) nanowires (NWs) are electrochemically prepared with dopant followed by functionalization with probe DNA (pDNA) sequence through electrostatic interaction. Various lengths of pDNA sequences (10-, 20- and 30-mer) are conjugated to the P3MT NWs respectively followed with hybridization with their complementary target DNA (tDNA) sequences. The nanoscale photoluminescence (PL) properties of the P3MT NWs are studied throughout the whole process at solid state. In addition, the correlation between the PL enhancement and the double helix DNA with various lengths is demonstrated.

Ion separation of binary metallic aqueous solutions at acidic Langmuir monolayer surfaces

We focused on analyzing the capability of the acidic monolayer surfaces for separation of toxic metal ions out of house-prepared binary inorganic ionic solutions such as calcium-lead, calcium-chromium, calcium-copper, and calcium-zinc aqueous systems. The affinities of the films to toxic metal ions were analyzed by using Fourier transform infrared spectroscopy. A model considering both the electrochemical and thermodynamic aspects was also applied to quantify the surface ion affinities. It is noted that surface ion binding capability for binary ionic solutions can be much different from that for pure ionic solutions. As a result, surface binding constants were found to be 4.5 × 106 for lead ions, 1.5 × 106 for chromium ions, 5.5×105 for copper ions, and 6 ×104 for zinc ions, respectively, at pH=5.5. For the separation experiments done at pH=5.5, lead, copper, zinc ions were separated more efficiently from the mixed ionic solutions by the factors of ca. 30,000, 10,000, 3,700, and 400, respectively, compared to calcium ions of which binding constant is 1.5 × 102. Interestingly, when compared to corresponding pure ionic systems, copper and lead ions were separated as much, while chromium and zinc ions were less by the factor of 500 and 50, respectively.

Huge Enhancement of Luminescence from a Coaxial-Like Heterostructure of Poly(3-methylthiophene) and Au

Recently, the light-matter interaction at nanoscale has attracted great interest from physicists, chemists and material scientists, as it gives peculiar optical properties that couldn’t be observed at the bulk scale. The synthesis and characterization of organic-inorganic heterostructures forming quantum dots, nanowires or nanotubes provide opportunities to understand their photophysical mechanism and to apply optoelecronic devices. Herein, we report a huge enhanced luminescence in a coaxial-like heterostructured poly (3-methylthiophene) (P3MT) with Au. We electrochemically synthesized P3MT nanowires (NWs) on a nanoporous template, and sequentially deposited Au on the surface of P3MT NWs. The diameter of heterostructured P3MT/Au NWs was about 200 nm, where the cladding-shape Au were about 10 nm. The visible range absorbance, with two new absorption peaks of P3MT/Au NWs, was significantly increased compared with that of P3MT NWs. Accordingly, the photoluminescence (PL) of a P3MT/Au NW was enormously increased; up to 170 times compared to that of P3MT NWs. More interestingly, an unexpected enhancement of PL was observed from cross-junction point of P3MT/Au NWs. The abnormal PL properties of P3MT/Au NWs were attributed to the charge transfer and the surface plasmon resonance between the cladding-shape Au and the core-shape P3MT, which resulted in the enhanced quantum yield. This incites us to reconsider the light-matter interaction in polymer-metal hybrid structures applicable for high-performance optoelectronic devices.

Temperature-Dependent Phase Behavior of Langmuir Films of 10,12-Pentacosadiynoic Acid at the Air/Water Interface and Its Effects on Chromatic Stability of the Polymerized Langmuir-Schaefer Films

The effect of temperature on the two-dimensional phase of 10,12-pentacosadiynoic acid (PCDA) Langmuir films at the air/water interface was investigated. The temperature of the Langmuir films was precisely controlled from 5 to 50 °C and their surface isotherms and in-situ visible absorption spectra were acquired. Depending on the temperature, the PCDA Langmuir films were found to be classified into a liquid-condensed (low temperatures, 5 and 25 °C) and a liquid-expanded phase (high temperatures, 40 and 50 °C). After polymerizing the PCDA Langmuir films with 254 nm UV light at the specific temperatures, the films were transferred to hydrophobic glass using the Langumir-Schaefer (LS) method. Upon thermal and pH stimuli, their chromatic transition characteristics were analyzed by visible spectroscopy. The liquid-condensed films were found to be more susceptible to thermal stimulus than the liquid-expanded films. The latter also showed remarkable chromatic stability against the pH in the region from 2 to 11, compared to the former. Thus, when sturdy films are required, the multilayered PCDA LS films prepared at the liquid-expanded phase are more suitable than the liquid-condensed films, and vice versa. This result is expected to be very useful for controlling the sensitivity and stability of polydiacetylene-based sensory systems simply by changing the polymerization temperature, even without synthesizing new monomers.