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ABSTRACT: In this feature article, we briefly review the new methods we have utilized recently in the investigation of morphology and
phase behavior of block copolymers. We first describe the chromatographic fractionation method to purify block copolymers
from their side products of mainly homopolymers or block copolymer precursors inadvertently terminated upon addition of the
next monomer in the sequential anionic polymerization. The chromatographic method is extended to the fractionation of the
individual block of diblock copolymers which can yield the diblock copolymer fractions of different composition and molecular
weight, which also have narrower distributions in both molecular weight and composition. A more detailed phase diagram could
be constructed from the set of block copolymer fractions without the need of acquiring many block copolymers each prepared
by anionic polymerization. The fractions with narrow distribution in both molecular weight and composition exhibit better
long-range ordering and sharper phase transition. Next, epitaxial relationships between two ordered structures in block copolymer
thin film is discussed. We employed the direct visualization method, transmission electron microtomography (TEMT) to scrutinize
the grain boundary structure.
Keywordsblock copolymer–molecular characterization–chromatography–phase transition–epitaxial grain boundary–transmission electron microtomography
Macromolecular Research 05/2012; 17(6):365-377. · 1.15 Impact Factor
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ABSTRACT: An HPLC column with a self-contained temperature control device was constructed for preparative temperature programmed interaction
chromatography. Two Peltier plates were attached to a large bore column (120×22 mm i.d.) and the column temperature was controlled
by PID mode feed back control. At a flow rate of 1.5 mL/min, the column temperature could be increased and decreased at a
rate as high as 50 °C/min and 10 °C/min, respectively, which is much faster than using a column jacket and bath/circulator.
The rapid heating and cooling rates allows a high repetition rate of chromatographic fractionation. The performance of the
temperature controllable column was demonstrated successfully by the fractionation of homo-polymer precursors from diblock
copolymers.
Keywordspolymer fractionation–HPLC column–temperature control–Peltier device–temperature gradient interaction chromatography
Macromolecular Research 04/2012; 16(6):544-548. · 1.15 Impact Factor
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ABSTRACT: A phase diagram was constructed for a polystyrene-block-polyisoprene (PS-b-PI, M(W) = 32 700, f(PI) = 0.670) in thin films on Si wafer as a function of film thickness over the range of 150-2410 nm (7-107L(0) (L(0): domain spacing)). The PS-b-PI exhibits a variety of ordered phases from hexagonally perforated lamellar (HPL) via double gyroid (DG) to hexagonally packed cylinder (HEX) before going to the disordered (DIS) phase upon heating. The morphology of the PS-b-PI in thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography. In thin film, the phase transition temperature is difficult to be determined unequivocally with in situ heating processes since the phase transition is slow and two phases coexist over a wide temperature range. Therefore, in an effort to find an "equilibrium" phase, we determined the long-term stable phase formed after cooling the film from the DIS phase to a target temperature and annealing for 24 h at the temperature. The temperature windows of stable ordered phases are strongly influenced by the film thickness. As the film thickness decreases, the temperature window of layer-like structures such as HPL and HEX becomes wider, whereas that of the DG stable region decreases. For the films thinner than 160 nm (8L(0)), only the HPL phase was found. In the films exhibiting DG phase, a perforated layer structure at the free surface was found, which gradually converts to the internal DG structure. The relief of interfacial tension by preferential wetting appears to play an important role in controlling the morphology in very thin films.
ACS Nano 06/2010; 4(6):3109-16. · 10.77 Impact Factor
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ABSTRACT: In recent years, two-dimensional liquid chromatography (2D-LC) has been used increasingly for the analysis of synthetic polymers. A 2D-LC analysis provides richer information than a single chromatography analysis at the cost of longer analysis time. The time required for a comprehensive 2D-LC analysis is essentially proportional to the analysis time of the second dimension separation. Many of 2D-LC analyses of synthetic polymers have employed size exclusion chromatography (SEC) for the second-dimension analysis due to the relatively short analysis time in addition to the wide use in the polymer analysis. Nonetheless, short SEC columns are often used for 2D-LC analyses to reduce the separation time, which inevitably deteriorates the resolution. In this study, we demonstrated that high temperature SEC can be employed as an efficient second-LC in the 2D-LC separation of synthetic polymers. By virtue of high temperature operation (low solvent viscosity and high diffusivity of the polymer molecules), a normal length SEC column can be used at high flow rate with little loss in resolution.
Journal of chromatography. A 05/2009; 1216(21):4606-10. · 4.19 Impact Factor
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ABSTRACT: Uniform nanodonuts: Stable toroidal micelles that have a highly uniform size and shape spontaneously self-assemble from a selective THF/ethanol solvent mixture (see 3D AFM image). The donut-shaped micelles can be used as a template to grow gold nanoparticles, which form along the ring surface.
Angewandte Chemie International Edition 05/2009; 48(25):4594-7. · 13.45 Impact Factor
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ABSTRACT: We investigated the epitaxial phase transition from double gyroid (DG) to hexagonally packed cylinder (HEX) phases of a polystyrene-b-polyisoprene diblock copolymer in a thin film on a Si wafer substrate. The internal structure of the thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography (TEMT). TEMT allows observation of the 3D-image of coexisting DG and HEX directly. Good domain orientation in the thin film and direct 3D-imaging of TEMT made it possible to observe the coexisting phase of DG and HEX, and a new epitaxial transition path from DG to HEX was found.
Journal of the American Chemical Society 01/2009; 131(1):46-7. · 9.91 Impact Factor
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ABSTRACT: The retention behavior of star-shaped polystyrene (PS) at the liquid chromatographic critical condition of linear PS was investigated. The star-shaped PS samples were prepared by anionic polymerization of styrene and subsequent linking of the polystyryl anions with divinylbenzene. The linking reaction yields a series of star-shaped PS with different number of branches of equal length. Three star-shaped PS samples with different arm molecular weight (MW) were prepared. To investigate the MW (hence the branch number) dependence of the LCCC (liquid chromatography at the critical condition) retention, the two-dimensional liquid chromatography method was usedfirst separating the polymers with respect to the molecular weight and subsequently separating the effluent by LCCC. Two different pore size columns were used for the LCCC separation to investigate the pore size dependence. The LCCC retention shows a very complex behavior. The retention time of the star-shaped PS shows a strong variation with MW (branch number) at the coelution condition of linear PS, and the deviation from the coelution behavior is more serious at a smaller pore sized column. The peculiar LCCC retention behavior was successfully delineated by a lattice Monte Carlo method taking into account the excluded volume and weak attractive interaction of the chain ends.
04/2008;
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ABSTRACT: We report on mixed surface micellization behavior of two diblock copolymers: PS-b-P2VP (Mw = 56 000, wPS = 50%) and PS-b-PMMA (Mw = 50 000, wPS = 50%). Both diblock copolymers were synthesized by sequential anionic polymerization and have narrow molecular weight distributions. PS-b-P2VP and PS-b-PMMA were spread at the air−water interface in dilute chloroform solution (0.5 mg/mL) by two different methods: (1) spreading of a premixed solution and (2) separate spreading of each block copolymer solutions sequentially. The π−A isotherms were measured at different subphase pH, and the morphology of the surface micelles was investigated by atomic force microscopy after transferring to a Langmuir−Blodgett film onto a silicon wafer. The ionization of the P2VP block induced different morphology at low pH from which the aggregated structure of block copolymers in micelles could be delineated. When PS-b-P2VP and PS-b-PMMA are spread as a premixed solution, two block copolymers form surface micelles sharing a PS core and mixed corona of P2VP and PMMA chains while independent PS-b-P2VP micelles and PS-b-PMMA micelles coexist when the block copolymers were spread separately. These results indicate that the surface micellization takes place rapidly after spreading, and there is no observable exchange of the block copolymers between the micelles in a reasonable time span.
02/2008;
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03/2007;
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ABSTRACT: A two-dimensional liquid chromatography (2D-LC) method, normal phase liquid chromatography (NPLC) for one dimension and reversed phase liquid chromatography (RPLC) for the other dimension, was employed to map the molecular weight distribution (MWD) of the individual blocks of a polystyrene-block-polyisoprene (PS-b-PI) diblock copolymer. The first-dimension (1st-D) NPLC separates PS-b-PI according to the PS block length while the second-dimension (2nd-D) RPLC separates PS-b-PI according to the PI block length. For the first-dimension NPLC separation, the column temperature was controlled to improve the resolution while the 2nd-D RPLC was run isothermally to reduce the separation time. The MWD information of individual blocks provides equivalent information to MWD and chemical composition distribution of a block copolymer. In this analysis, the effluent from the 1st-D LC separation is concentrated before the injection to the 2nd-D LC by use of a trap column, which allows an efficient interface between the two LC separations. Over 200 different block copolymer species could be identified from the 2D-LC chromatogram.
01/2007;
