Kunihide Izumi

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.

Growth Rate of Isotactic Polystyrene Crystals in Thin Films

The lateral crystal growth rate of isotactic polystyrene lamellae developing in thin films (ranging from 20 nm to 500 nm) decreases with decreasing film thickness. The decrease in growth rate is inversely proportional to the film thickness: G ( D )= G (∞)(1- d / D ), where G ( D ) is the growth rate in a film of thickness D , G (∞) is the growth rate in the bulk, and d is a constant with a value of approximately 6 nm. Additionally, d is observed to be independent of the crystallization temperature; molecular weight and substrate material used in this study. It is proposed that the constant value of d corresponds to the tube diameter in the reptation model of polymer dynamics, and that near the substrate this diameter is reduced, thereby reducing the mobility of the molecules, and consequently the crystal growth rate.

X-ray topography of lysozyme crystals

Laue topography of orthorhombic and tetragonal lysozyme crystals has been carried out using synchrotron radiation. A water filter, 5 mm in thickness, was effective to avoid radiation damage. The orthorhombic crystals grown at 38°C showed strong asterisms. The tetragonal crystals grown at room temperature and the orthorhombic crystals incubated at room temperature from small crystals emerging at 38°C did not show asterism but showed white bands in black Bragg spots resembling the shape of the crystals. Straight bands directed to the radial directions of the diffraction pattern, wavy bands parallel to the c-axis of the orthorhombic crystal and straight twisted bands parallel to several directions in the tetragonal crystal were also observed.

The morphology of isotactic polystyrene crystals grown in thin films: the effect of substrate material

Thin isotactic polystyrene films (∼50 nm thick) have been crystallized from the melt on various substrate materials (carbon, glass, mica, polyimide sheet and silicon). The morphology of the crystals has been examined using atomic force microscopy, and was found to be dependent on the nature of the substrate, with two basic types of crystal forming. Crystals either develop around giant screw dislocations, or around small bundles of lamellae growing perpendicular to the substrate surface. It has further been observed that the number of screw dislocations generated in the lamellae is also dependent on the substrate, as is the growth rate of the spiral terraces. These effects are interpreted in terms of interactions between the molecules in the melt and the substrate surface.

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.

The Effects of Irradiation of 100 KeV Electrons on Alkali Halide Crystals; The Point Defect Coagulates in NaCl and KCl Irradiated at Room Temperature

Thin films of KCl and NaCl single crystals prepared by chemical polishing were examined by an electron microscope. During the observation, the thin films were damaged by electron beam used for the image formation. As a result of electron irradiation at room temperature, plate shaped defects parallel to one of the {100} planes and elongated in one of the directions were formed in both kinds of crystals. The maximum dimension of them was about 1 µ in long axis 1000∼3000 A in short axis and ∼100 A in thickness. It is supposed that these plates correspond to the small alkali metal colloids which were considered to be the origin of X-band absorption in the optical measurement, because the behaviour of the plates during heat treatment between room temperature and 300°C showed good agreement with that of the colloids.

Morphological Diversity in the Crystal Growth of Potassium and Rubidium Dichromates in Gelatin Gel

We have found that the crystals of rubidium dichromate (Rb 2 Cr 2 O 7 ) grown in gelatin gel have a rich variety of morphologies such as platelike, spherulitic and diffusion-limited aggregation (DLA)-like shapes. The morphological diagram has been determined in the range of solute and gelatin concentrations from 1.0 to 4.0%, 0.1 to 7.0%, respectively. The diagram corresponds to that of potassium dichromate (K 2 Cr 2 O 7 ) which is similar to Rb 2 Cr 2 O 7 in the crystal structure and physico-chemical properties. However, featherlike crystals have grown in the region of the diagram where the unique helical K 2 Cr 2 O 7 crystals grow. We discuss the morphological changes of two kinds of dichromate crystals grown in gelatin gel.

The lamellar thickness of melt crystallized isotactic polystyrene as determined by atomic force microscopy

Atomic force microscopy has been used to investigate the morphology of isotactic polystyrene lamellae growth from the melt in very thin films (∼ 50 nm in thickness). It is shown that atomic force microscopy can elucidate the crystal morphology and provide quantitative measurements of the step height (between successive crystal layers of a spiral overgrowth terrace) corresponding to the long spacing, provided suitable procedures are employed.

Atomic Force Microscopy of Isotactic Polystyrene Crystals

The growth of isotactic polystyrene crystals from a thin melt film is examined by atomic force microscopy. The crystals protrude from the film up to about 100 nm to form a hexagonal spiral with a hollow screw dislocation at the center; the distance between neighboring steps of the growth spiral is discussed on the basis of the critical nucleus. The entire crystal has collapsed to the substrate. An amorphous layer a few nanometers thick covers the surface of the crystal. At the crystal-liquid interface, a concave region about 2 nm deep extends ca. 400 nm.