Ken Taguchi

Growth shape of isotactic polystyrene crystals in thin films

The crystal growth of isotactic polystyrene (it-PS) is investigated in very thin, 11 nm thick films. The it-PS crystals grown in the thin films show quite different morphology from that in the bulk. With decreasing crystallization temperature, the branching morphology in a diffusion field appears: dendrites and compact seaweed. The branching morphology is formed through a morphological instability caused by the gradient of film thickness around a crystal; the thicker the film thickness, the larger is the lateral growth rate of crystals. Regardless of the morphological change, the growth rate as well as the lamellar thickness depends on the crystallization temperature as predicted by the surface kinetics.

CRYSTAL GROWTH OF ISOTACTIC POLYSTYRENE IN ULTRATHIN FILMS: FILM THICKNESS DEPENDENCE

The film thickness dependence of crystal growth is investigated for isotactic polystyrene (it-PS) in thin films for thicknesses from 20 down to 4 nm. The single crystals of it-PS grown at 180°C in the ultrathin films show a morphology typical of diffusion-controlled growth: dense branching morphology and fractal seaweed. The characteristic length of the morphology, i.e., the width of the branch, increases with decreasing film thickness. The thickness dependence of the crystal growth rate shows a crossover around the lamellar thickness of 8 nm. The thickness dependences of the growth rate and morphology are discussed in terms of the diffusion of chain molecules in thin films.

Crystal Growth of Isotactic Polystyrene in Ultrathin Films: Thickness and Temperature Dependence

The growth rate and morphology of isotactic polystyrene crystals grown in ultrathin films have been examined experimentally in terms of the dependences both on the film thickness and on the crystallization temperature. We have found that the thickness dependence of growth rate, G, shows a crossover change when the film thickness becomes comparable with the lamellar thickness of the polymer crystals, irrespective of the temperatures. The morphology of crystals grown in ultrathin films shows a branching typical of dendrites, the growth of which is supposed to be controlled by a diffusion field. The change in the tip width of the dendrites with crystallization temperature follows the expected dependence of the Mullins–Sekerka stability length, ℓMS ∝ (D/G)1/2, determined by the diffusion coefficient, D, and the growth rate. The results confirm that a diffusion field plays an essential role in the evolution of the structure.

Screw dislocation lines in lysozyme crystals observed by Laue topography using synchrotron radiation

Laue topography of the tetragonal crystals of hen egg-white lysozyme has been carried out using synchrotron radiation. Straight-line images extending from the core part to the growth fronts were observed and interpreted as dislocations. They had the displacement vectors parallel to the line; they are similar type of dislocations common to the crystals grown from solutions. The Laue spots showed uniform distortion. The water filter 10 mm thick was effective in avoiding radiation damages.

Morphology, growth rate, and lamellar thickness of polymer crystals

At high supercoolings, isotactic polystyrene and polybutene-1 have a rounded crystal shape, suggesting kinetic roughening. Still, the growth rates of these polymer crystals show the supercooling dependence derived for nucleation controlled growth. On the other hand, isotactic poly-4-methylpentene-1 1,4 trans-polybutadiene at higher crystallization temperatures and polyethylene at high pressures show a rounded crystal shape: thermal roughening. Again, the growth rate is described by the nucleation theory. On the basis of these observations, we propose a crystallization kinetics taking account of the entropic barrier that was originally proposed by Sadler.

Kinetics of phase separation and coarsening in dilute surfactant pentaethylene glycol monododecyl ether solutions

We investigated the phase separation phenomena in dilute surfactant pentaethylene glycol monodedecyl ether (C(12)E(5)) solutions focusing on the growth law of separated domains. The solutions confined between two glass plates were found to exhibit the phase inversion, characteristic of the viscoelastic phase separation; the majority phase (water-rich phase) nucleated as droplets and the minority phase (micelle-rich phase) formed a network temporarily, then they collapsed into an usual sea-island pattern where minority phase formed islands. We found from the real-space microscopic imaging that the dynamic scaling hypothesis did not hold throughout the coarsening process. The power law growth of the domains with the exponent close to 1/3 was observed even though the coarsening was induced mainly by hydrodynamic flow, which was explained by Darcys law of laminar flow.

Dynamic Light Scattering Studies on Crystallization of Isotactic Polystyrene from Dilute Solutions at High Supercoolings

Crystallization of isotactic polystyrene (it‐PS) from dilute solution at high supercooling has been investigated by dynamic light scattering (DLS). We successfully obtained simultaneously, in situ in solutions, the time developments of both random coils of it‐PS molecules and the growing crystals. The size of coils remains constant during growth, while the crystals pass through two stages, that is, an induction period at the early stage with very slow growth rates and a subsequent linear growth stage. It is confirmed that the temperature dependence of the linear growth rates, determined by DLS, agree well with that determined by electron microscopy. The temperature dependences of the growth rate and the inverse of induction time are dependent on the viscosity of solvent, which indicates that all dynamics are dominated by the segmental motion of polymer chains in solution at high supercoolings (low temperatures). Two possibilities are proposed for the induction period.