Insun Park

Pohang University of Science and Technology, Geijitsu, North Gyeongsang, South Korea

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Publications (12)27.37 Total impact

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    ABSTRACT: The electron density map of a block copolymer thin film having the hexagonally perforated layer (HPL) structure was directly obtained from the measured grazing-incidence small-angle X-ray scattering (GISAXS) pattern, exploiting the multiple-scattering phenomena present in GISAXS. It is shown that GISAXS is in principle equivalent to three-beam diffraction, which has been used to extract phases of diffraction peaks. In addition, X-ray reflectivity analysis has been performed which, when combined with the GISAXS results, provides full details of the HPL structure.
    Journal of Applied Crystallography 06/2007; 40(Part 3):496-504. · 3.34 Impact Factor
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    ABSTRACT: Block copolymer ordering in thin films on a preferentially wetting flat substrate is studied using a polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer, which forms PMMA cylinders in bulk. Tapping-mode AFM and cross-sectional TEM were employed to characterize the thin film ordered structure of the PS-b-PMMA on a flat silicon surface with native oxide that is preferentially wetted by PMMA blocks. The PS-b-PMMA in thin film develops hexagonally perforated layer (HPL), which is different from its cylindrical bulk morphology. The HPL structure of PS-b-PMMA exhibits islands and holes at the surface, which persists up to the film thickness as high as 6L 0 . Surface-induced reorganization of the block copolymers on PMMA-preferring flat surface may be responsible for the formation of the layerlike nonbulk structure of HPL, which has been templated from the flat surface and propagated into a multilayered HPL films.
    Macromolecules. 12/2005; 39(1).
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    ABSTRACT: We investigated the phase transition behavior from the hexagonally perforated layer (HPL) to the gyroid (G) phase in supported thin film of a polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer (Mn = 34.0 kg/mol, wtPI = 0.634) by grazing-incidence small-angle X-ray scattering. After annealing at 120 °C, the PS-b-PI thin film spin-coated on silicon wafer exhibited HPL morphology with its lamellae highly oriented parallel to the substrate up to a thickness as much as 1 μm. The interface-induced orientation allowed us to obtain a well-developed diffraction pattern in the absence of external mechanical strain to align the domains. The comparison with the computer-simulated diffraction pattern revealed that the HPL structure has mosaic grains oriented randomly in-plane with ABC stacking and undetectable amount of AB stacking. Upon heating, the HPL phase undergoes a phase transition to the G phase. The phase transition occurred epitaxially converting the HPL layers to the {121} planes of the G structure maintaining the G {121} plane oriented parallel to the substrate. This behavior is in contrast with the HPL to G phase transition found from the shear-oriented HPL samples, in which the G {121} plane is randomly oriented around the G [111] axis.
    Macromolecules. 11/2005; 38(25).
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    ABSTRACT: The grazing incidence small-angle X-ray scattering (GISAXS) from structures within a thin film on a substrate is generally a superposition of the two scatterings generated by the two X-ray beams (reflected and transmitted beams) converging on the film with a difference of twice the incidence angle (R i) of the X-ray beam in their angular directions; these two scatterings may overlap or may be distinct, depending on Ri. The two scatterings are further distorted by the effects of refraction. These reflection and refraction effects mean that GISAXS is complicated to analyze. To quantitatively analyze GISAXS patterns, in this study we derived a GISAXS formula under the distorted wave Born approximation. We applied this formula to the quantitative analysis of the GISAXS patterns obtained for various compositions of polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer thin films on silicon substrates with native oxide layers. This analysis showed that the diblock copolymer thin films consist of hexagonally packed cylinder (HEX) structures, hexagonally perforated layer (HPL) structures, and gyroid structures, all with characteristic preferential orientations, depending on the composition of the copolymer. This is the first report of GISAXS studies of HEX, HPL, and gyroid microdomain structures in block copolymer thin films. Moreover, our study also provides a simple method for understanding GISAXS patterns and for determining the structure factor or interference function from them. Thus, the use of the GISAXS technique with our derived GISAXS formula as a data analysis engine is a very powerful tool for determining the morphologies of polymer thin films on substrates.
    Macromolecules. 01/2005; 38(10).
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    ABSTRACT: An interaction-controlled HPLC technique has been developed to analyze homopolymer precursors in block copolymer systems that are not easily identified by size exclusion chromatography (SEC) and to obtain block copolymers that are homopolymer-free and compositionally narrower than the as-synthesized ones. We demonstrate that a "single peak" in SEC does not necessarily mean that the block copolymers are free of homopolymers (due to limitations in the SEC analysis of block copolymers) and propose to employ the interaction-controlled HPLC strategy for rigorous analysis and purification of block copolymers in terms of their chemical heterogeneity.
    Journal of the American Chemical Society 08/2004; 126(29):8906-7. · 10.68 Impact Factor
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    ABSTRACT: There have been significant advances in the synthesis of block copolymers with complex chain architectures by anionic polymerization. However, it is inevitable that as-synthesized block copolymers will contain prematurely-terminated homopolymer precursors, due to any trace amount of impurities or side reactions from the second monomer. The significance of this report is to introduce a interaction chromatography (IC) technique with an emphasis of block copolymer analysis and separation (i.e. fractionation) at a semi-prep scale ( 0.1 gram). We will present a semi-prep IC technique on ¡°as-synthesized¡+/- block copolymers (a) to obtain block copolymer samples that are synthetically challenging or unattainable and (b) to show that it is complement and even superior to the prevalent SEC technique for the analysis and fractionation of as-synthesized chemically heterogenous copolymers.
    01/2004;
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    ABSTRACT: We have studied the thin film morphology of a diblock copolymer. A commercially available PS-b-PMMA was fractionated by HPLC to remove homopolymer contaminant and to fractionate it into several fractions of different compositions. The block copolymer samples were spin-coated on silicon wafers and their surface structures and the structures within the film were studied using tapping mode atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS), respectively. We found that the morphology changes sensitively with the composition of the block copolymers. Three different morphologies-cylinder, hexagonally perforated layer, and lamellar structures were observed. The parallel cylinder morphology has their (100) plane parallel to film plane near perfectly. The hexagonally perforated layered structure appears more stable in thin film than in bulk.
    01/2004;
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    ABSTRACT: The chain architecture dependence of the retention behavior of block copolymers in the temperature gradient interaction chromatography (TGIC) and liquid chromatography at the critical condition (LCCC) was investigated. For the purpose, polystyrene (PS)/polybutadiene (PB) diblock (SB), SBS triblock, and BSB triblock copolymers were prepared by sequential anionic polymerization and further fractionated by reversed-phase TGIC to obtain a set of the block copolymers with high purity, narrow distribution, and matched block length. In the TGIC separation with C18 bonded silica stationary phase and a mixture of CH2Cl2/CH3CN mobile phase, retention of the three block copolymers with matched molecular weight and composition shows a significant architecture effect:  SBS elutes significantly earlier while BSB or SB elute later at similar retention volume. It indicates that the polymer−stationary phase interaction is less effective for the PB block located at the middle of the chain than the blocks located at the chain end. In LCCC separation at the critical condition for PB block, SBS is eluted early while SB and BSB were eluted later at the same retention time. Therefore, triblock copolymer with an invisible middle block behaves differently from those having invisible end block(s). This behavior is consistent with the theoretical prediction by Guttman et al. [Macromolecules 1996, 29, 5723].
    Macromolecules 10/2003; 36(22). · 5.93 Impact Factor
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    ABSTRACT: A polar polydimethylsiloxane terminator was prepared and reacted with living copolymer anion of styrene and butadiene, to synthesize end-functionalized styrene–butadiene rubber (SBR). As a polar functional terminator, poly(ethylene glycol)-poly(dimethylsiloxane) block copolymer (PEG-PDMS) containing a chlorosilyl moiety at one chain end (1) was synthesized by two-step hydrosilylation. End capping of poly(styrene–butadiene) living anion with PEG-PDMS terminator (1) afforded polymers with polar poly(dimethylsiloxane) end groups. PEG-PDMS terminated SBR, SBR-1, showed higher interaction with silica particles by microscophy and chromatography. Dynamic-mechanical analysis on silica composites of SBR-1 strongly supports the assumption that the PEG-PDMS end groups behave as polar functional groups, showing increase of the glass transition temperature (Tg) and storage modulus in the composite of SBR-1 with silica particles. The SBR-1/silica composite showed lower tan δ at 60°C and higher tan δ at 0°C as compared to SBR-Sn/silica composite.
    Polymer Journal 09/2002; 34(9):674-681. · 1.50 Impact Factor
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    ABSTRACT: Novel thermoreversible gelation behavior of aqueous solutions of ABA-type triblock copolymers composed of the central polyethylene oxide (PEG) block and two poly(D,L-lactic acid-co-glycolic acid) side blocks was found. Phase transition characteristics, such as critical gel concentration (CGC) and lower and upper critical gel temperature (CGT), are closely related to the molecular structure of the triblock copolymers. The CGC and the lower CGT both increases with increasing PEG/PLGA molecular weight ratio. Increasing the GA content in PLGA block induces a somewhat higher CGC. The copolymer forms micelles with a PLGA loop core and a PEG shell in water. Also grouped micelles are identified seemingly due to the bridging of two micelles sharing two PLGA blocks of a block copolymer chain. As the temperature increases the association of micelles increases, which results in gelation. The ABA-type copolymers exhibit a relatively low CGC (<10%) and low sol-gel transition temperatures compared to BAB-type copolymers. As the temperature increases further gel-sol transition is observed, which would result from the shrinkage of micelles with temperature increase. The hydrodynamic size of the micelles is monitored by dynamic laser scattering, and a possible gelation mechanism was suggested.
    Journal of Biomedical Materials Research 09/2002; 61(2):188-96.
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    Macromolecules 01/2002; 35(15):6067-6069. · 5.93 Impact Factor
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    Macromolecular Rapid Communications - MACROMOL RAPID COMMUN. 01/2001; 22(8):587-592.