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  • 1
    Electronic Resource
    Electronic Resource
    Small-angle x-ray scattering analysis of polymer-protected platinum, rhodium, and platinum/rhodium colloidal dispersions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5627-5638 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Formations of poly(N-vinyl-2-pyrrolidone)(PVP)-metal ion (Pt, Rh or Pt/Rh(1/1)) complexes in H2O/C2H5OH ("polymer–metal ion complexes") before alcohol-reduction and PVP–Pt, Rh, or Pt/Rh(1/1) metal cluster ("polymer–metal cluster") after alcohol-reduction were studied by small-angle x-ray scattering (SAXS). SAXS intensity of the solution containing polymer–metal ion complexes is higher than that of the reference polymer solution without metal ions, suggesting that concentration fluctuations of polymer segments are enhanced due to the formation of polymer–metal ion complexes. Spatial distributions of metal clusters in colloidal dispersions are different from each other among the cases of Pt, Rh, and Pt/Rh(1/1) colloidal dispersions. The superstructure (greater than 10.0 nm in diameter), whose average sizes highly depend on the metal element employed, are formed. These superstructures are composed of several fundamental clusters with a diameter of ∼2.0–4.0 nm. Colloidal dispersions of Rh form a percolation network of clusters with an average period of ∼6.0 nm inside the higher-order organization of its superstructure. Experimental results concerning the physical aging show the high stability of colloidal dispersions of metal clusters protected by water-soluble PVP. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477181
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  • 2
    Electronic Resource
    Electronic Resource
    Formation of droplets with a very narrow size distribution in mixtures subjected to shear flow. I. Shear rate dependence (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6963-6972 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The phase-separated structures of a semidilute solution of off-critical polymer mixtures composed of polystyrene (PS) and polybutadiene (PB) in a common solvent of dioctylphthalate (DOP) under steady shear flow are investigated by light scattering as a function of shear rate γ(overdot). Light scattering patterns show multiple-order scattering maxima up to the 13th order or more in a weak shear regime, revealing formation of droplets with surprisingly uniform size having a relative standard deviation of droplet radius σR∼0.03. The average droplet radii R¯x parallel and R¯z perpendicular to the flow direction are proportional to γ(overdot)−1, with an average aspect ratio v¯R≡R¯x/R¯z of 2 independent of γ(overdot) in the weak shear regime. The result obtained in the average particle size is in good agreement with that predicted by Taylor's theory for a single droplet case, but the extreme uniformity in size distribution would not be trivial and be worth it for future theoretical considerations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476112
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  • 3
    Electronic Resource
    Electronic Resource
    Heterogeneous percolation-to-cluster transition in phase separation of an off-critical polymer mixture (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3612-3620 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Phase separation kinetics of an off-critical polymer mixture involving percolation-to-cluster transition (PCT) was investigated by time-resolved light scattering and by transmission optical and electron microscopies. The process involving a splitting of a single peak in the light scattering profile into a double peak was observed for the first time after the onset of PCT. Each peak changes with time (t) according to different evolution modes, e.g., the first peak wave number qm,1 evolved according to the power law of percolated structures (qm∼t−α; α=0.9), while the time evolution of the second peak wave number qm,2 is very slow, which corresponds to the growth of cluster of the droplets after PCT. Furthermore, the real space pictures and the light scattering analysis reveal that a cluster of the small spherical droplets and the locally percolating domains coexist for a very long time. The percolating domains are larger than the small droplets, minor in volume fraction, and formed in bulk and they are developed into sheet-like grains with their surfaces parallel to the glass surface. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478229
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental study of dynamics of topological defects in nematic polymer liquid crystals (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 1618-1625 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of stringlike defects and the shrinkage and annihilation processes of individual defect loops in a nematic polymer liquid crystal have been experimentally investigated. In 40〈t〈500 s, the line density of defects ρ scales as ρ(t)∼t−1, as expected by theory and as found in the experimental studies of some low molecular weight (LMW) liquid crystals. For individual loops, they first change their complex shape into a circle, resulting in a rapid decrease in length, and then the circular loops continuously shrink. Before a complete annihilation, the relation between the radius R(t) of the circular loop and time t0−t, where t0 is the time to annihilation, is described by R2(t)=2Γ(t0−t)(t≤t0). The kinetic constant Γ determined from this polymer liquid crystal is 0.34∼0.38 μm2/s, much smaller than those (200∼300 μm2/s) obtained in some LMW liquid crystals. The small Γ is ascribed to the high viscosity of this polymer liquid crystal, compared with LMW liquid crystals. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475532
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  • 5
    Electronic Resource
    Electronic Resource
    Intermittency of droplet growth in phase separation of off-critical polymer mixtures (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 1225-1233 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Kinetics of the phase separation in binary off-critical mixtures of polybutadiene (PB) and polyisoprene (PI) was investigated as a function of quench depth and composition by using time-resolved light scattering. The kinetics for the off-critical mixtures is much slower than that for the critical mixture. The scattering maximum for the off-critical mixtures is very broad relative to that for the critical mixture. For the off-critical mixtures, the domain growth follows the same power law (qm∼t−α, Im∼tβ: α=0.25–0.33, β=0.75–1) in the long time limit covered in our experiments, independent of quench depth and composition. However, the domain growth became very slow before the long time limit under a certain condition (intermittency of the domain growth). In the regime where the intermittency was observed, the scaling exponents α and β depend on quench depth. The shallower the quench, the smaller the values of α and β and the longer the intermittent regime. These behaviors are largely different from those for the critical mixture for which the scaling exponents show almost the same value in the late stage for different quenches and the Langer–Bar-on–Miller or Chou–Goldburg scaling postulate is fulfilled. Scaled structure factor in the late stage of phase separation process was found to depend on quench depth, becoming broader as quench is shallower. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475484
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  • 6
    Electronic Resource
    Electronic Resource
    Crossover of domain-growth behavior from percolation to cluster regime in phase separation of an off-critical polymer mixture (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1634-1644 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-resolved light scattering has been used to investigate phase-separation dynamics for off-critical mixtures of polybutadiene (PB) and polyisoprene (PI) with a well defined phase diagram. Percolation-to-cluster transition (PCT) occurs in the course of the phase separation process for an off-critical mixture of the PB and the PI in the shallow quenches covered in this work. Before the onset of PCT occurs, the phase separation dynamics is fast, typically obeying qm∼t−0.9 and Im∼t2.7 ("percolation regime"), where qm is the scattering vector at the maximum scattered intensity Im. After the onset of PCT the time changes in qm and Im become very slow, and the phase separation process might appear to stop, if we observe the dynamics in a short time scale after the onset of PCT. The behavior corresponds to the results which Hashimoto et al. reported for the off-critical mixtures of poly(styrene-ran-butadiene) (SBR) and PB, and SBR and PI (spontaneous pinning of the domain growth) [J. Chem. Phys. 97, 679 (1992)]. However, it is shown in this paper that the droplets formed after PCT eventually grow according to the scaling law of qm∼t−n and Im∼t3n with n=1/4 to 1/3 ("cluster regime"), if we keep observing the phase separation process in the much longer time scale, beyond the time period over which the domain growth appeared to be pinned. To our knowledge, it is for the first time that such crossover of domain-growth behavior from percolation to cluster regime was observed via the intermittent time period over which the growth kinetics are apparently pinned. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474515
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  • 7
    Electronic Resource
    Electronic Resource
    Two-step phase separation of a polymer mixture. I. New scaling analysis for the main scattering peak (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6886-6896 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-resolved light scattering experiments have been performed on the two-step phase separation process for a binary mixture of deuterated polybutadiene and protonated polyisoprene with the critical composition. The first-step phase separation was induced by quenching the system from a temperature T0 in a single-phase state to T1. At various times in the late stage spinodal decomposition (SD) at T1, the mixture was further subjected to the second-step phase separation by temperature jump (T-jump) from T1 to T2 in such a way that the driving force for the phase separation increases and hence phase separation process is accelerated. The comparison between the single-step phase separation behavior from T0 to T1 or to T2 and the two-step phase separation behavior was made in terms of the time evolution of the main scattering peak arising from a dominant mode of the composition fluctuations developed in the phase separation process. To do so, we proposed and applied a new scaling method for the scattering peak position, qm,1, and intensity, Im,1, to explore the time evolution of the fluctuations for the two-step phase separation process. The new scaling method, which takes into account an abrupt change in the spatio-temporal scale of phase-separating system involved by the second-step T-jump clearly elucidates a nonlinear pathway according to which the initial structures developed in the first-step process is relaxed and transformed toward an equilibrium structure at T2 after the second-step process. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481317
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  • 8
    Electronic Resource
    Electronic Resource
    Two-step phase separation of a polymer mixture. II. Time evolution of structure factor (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6897-6909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonlinear time evolution of phase-separating structures in the two-step phase separation process was investigated for a deuterated polybutadiene–polyisoprene mixture by using a time-resolved light scattering technique. The mixture studied has a lower critical solution temperature type phase diagram with a spinodal temperature of 36 °C. The first-step phase separation via spinodal decomposition (SD) was conducted by a temperature jump (T-jump) from 23 °C to 42 °C, and to the late stage of the SD for varying time periods, t0, in order to develop phase-separated domains with varying characteristic size Λm,1. This phase separation was followed by the second-step T-jump to a higher temperature of 70 °C so that each phase-separated domain is again quenched into thermodynamically unstable region. Nonlinear time evolution processes of phase-separating structures after the second-step SD were explored as a function of size of the initial structures Λm,1. We found the following intriguing effects of the initial structures on further evolution of phase-separating structure via the second-step SD: (1) When Λm,1(very-much-greater-than)Λm,0 (characteristic length of composition fluctuations developed in the early stage SD after quenching the system from a single-phase state to 70 °C), small domains were evolved within the initial domains (defined as large domains) developed during the first-step SD process, while (2) when Λm,1≤Λm,0, the small domains were not developed, but only the large domains grew at a growth rate larger than that at 42 °C. In the former case (1), we succeeded in separating the scattering due to the small domains and that due to large domains from the observed scattering profile. The separation allows us to investigate a coupling of the time evolution of the large and small domains and nonlinear pathways for the system to achieve a new equilibrium structure after the second-step SD process. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481321
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  • 9
    Electronic Resource
    Electronic Resource
    Order-disorder transition of polystyrene-block-polyisoprene. I. Thermal concentration fluctuations in single-phase melts and solutions and determination of χ as a function of molecular weight and composition (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7765-7777 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Small-angle x-ray scattering (SAXS) from single-phase melts and solutions of polystyrene-block-polyisoprene (SI) having various degrees of polymerization N and compositions f were analyzed on the basis of Landau-type mean-field theory developed by Leibler. The effective Flory interaction parameter χeff per segment in melts and in semidilute aitch-theta solutions were determined from the mean-field analysis of the SAXS profiles obtained at temperatures higher than TMF, the crossover temperature above which the non-mean-field effects become less significant and the mean-field theory becomes a good approximation. It was found that χeff thus determined depends on N, f, volume fraction of the SI in the solution φp and the interaction parameter χ0 in melt: χeff=φpχ0 and χ0 is a function of f and N; χ0 at a given f is a decreasing function of N and that at a given N is approximately a quadratic function of f with a minimum at f(approximately-equal-to)1/2. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471656
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  • 10
    Electronic Resource
    Electronic Resource
    Void structure and vapor–liquid condensation in dilute deionized colloidal dispersions (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 10146-10151 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Void formation and vapor–liquid condensation in deionized dilute aqueous colloidal dispersions were studied for the same latex sample. The former was observed under density-matched conditions, while the latter was observed when the particles were denser than the dispersion medium. The critical concentration for void formation was found by direct observation using a confocal laser scanning microscope. Vapor–liquid condensation was observed for a dispersion of the same latex particles below the critical concentration. The critical concentrations for both phenomena were in agreement. The results clearly suggest an important role of a long-range electrostatic attractive interaction on the stability of the colloidal dispersion. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469916
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