The Optical Behavior of Polyethylene Spherulites

Polyethylene was crytallized from the molten film under temperature gradient. As a result, the optically positive spherulites were observed, though only the negative spherulites had been observed previOusly in polyethylene. When the radial structure units twisted regulary in a spherulite are formed parallel to the surface of the film, the spberulite is usually optically negative in polyethylene. In this study, the temperature gradient normal to the surface of the film gives so significant tilt of the radial structure units formed to the surface of the film that the radial refractive index becomes larger than the tangential one under the transmitted polarized light and the spherulites have optically positive behavior. The optical behaviors of the polyethylene spherulites and the crystallizing condition were studied and discussed

Crystallization of triethyl-citrate-plasticized poly(lactic acid) induced by chitin nanocrystals

The aim of this study was to gain a better understanding of the crystallization behavior of triethyl-citrate-plasticized poly(lactic acid) (PLA–TEC) in the presence of chitin nanocrystals (ChNCs). The isothermal crystallization behavior of PLA–TEC was studied by polarized optical microscopy, scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). Interestingly, the addition of just 1 wt % ChNCs in PLA–TEC increased the crystallization rate in the temperature range of 135–125 °C. The microscopy studies confirmed the presence of at least three distinct types of spherulites: negative, neutral, and ring banded. The ChNCs also increased the degree of crystallinity up to 32%, even at a fast cooling rate of 25¿°C min-1. The XRD studies further revealed the nucleation effect induced by the addition of ChNCs and thus explained the faster crystallization rate. To conclude, the addition of a small amount (1 wt %) of ChNC to plasticized PLA significantly affected its nucleation, crystal size, and crystallization speed; therefore, the proposed route can be considered suitable for improving the crystallization behavior of PLA.Peer ReviewedPostprint (author's final draft

Spherulite formation in obsidian lavas in the Aeolian Islands, Italy

The authors wish to gratefully acknowledge Andy Tindle (The Open University) for assistance with EMP analyses, and Richard Darton and David Evans (Keele University) for assistance with XRD and Prof Alun Vaughan and Nicola Freebody (University of Southampton) with Raman analyses. LAB is grateful to Sophie Blanchard for support with MATLAB. The authors acknowledge support from Keele University, and grants from the Mineralogical Society (UK and Ireland) and Volcanic and Magmatic Studies Group. The authors thank Silvio Mollo and Francesca Forni for their detailed and helpful comments.Peer reviewedPublisher PD

Real time imaging of two-dimensional iron oxide spherulite nanostructure formation

The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view. Spherulite structures with radial fibrillar branches have been found in various solids; however, their growth mechanisms remain poorly understood. Here, we report real time imaging of the formation of two-dimensional (2D) iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy (TEM). By tracking the growth trajectories, we show the characteristics of the reaction front and growth kinetics. Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes (5.5–8.5 nm). The radius of a spherulite nanostructure increases linearly with time at the early stage, transitioning to nonlinear growth at the later stage. Furthermore, a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches. The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth. A growth model is further established, which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth. [Figure not available: see fulltext.]

Two Distinct Types of Spherulite in Poly (ethylene oxide)

Fujiwara's oriented crystallization method was applied to poly (ethylene oxide) to obtain a uniform texture composed of parallel fibrils which correspond to the structure of a radial direction of spherulites. Two different x-ray diffraction patterns in crystallite orientation of the spherulite radius were obtained. From these patterns and crystallization conditions it could be determined that the spherulite radius has a [401] rotation axis below about 50℃ and two [421] and [421]rotation axes above about 50℃. A reasonable interpretation was given for these two ways of spherulitic crystallization, based on the growth features of lamellar crystals of poly (ethylene oxide). That is, it is concluded that a second order transition in poly (ethylene oxide) lamellar crystals near the temperature of 50℃ is responsible for the change of the rotation axis in spherulite radius

Phase transitions during membrane formation of polylactides. I. A morphological study of membranes obtained from the system polylactide-chloroform-methanol

The influence of solid-liquid demixing, liquid-liquid demixing and vitrification on the morphology of polylactide membranes has been investigated. To study the effects of crystallization of polylactides on the membrane and morphology, polylactides of varying stereoregularity were used. The polymers applied were poly--lactide (PLLA) and copolymers with different molar ratios of -lactide and -lactide [poly-L95/D5-lactide (PLA95), poly-L80/D20-lactide (PLA80) and poly-L50/D50-lactide (PDLLA)]. Solutions of polylactides in chloroform cast on a glass plate were immersed in methanol. From solutions containing the slowly crystallizing PLA80 or uncrystallizable PDLLA porous membranes were obtained if the phase separated system was removed from the nonsolvent bath within a few hours after immersion. After longer equilibration times in methanol the structure collapsed. The swelling in the nonsolvent methanol was too high to allow stabilization of the liquid-liquid demixed structure by vitrification. Stable membranes were easily obtained with more rapidly crystallizing polymers like PLLA. Casting solutions with low PLLA concentrations gave membranes with a cellular morphology due to liquid-liquid demixing by nucleation and growth of a polymer poor phase. Crystallization only played a role in the fixation of the liquid-liquid demixed structure. At increasing PLLA concentrations the demixing sequence gradually reversed to crystallization followed by liquid-liquid demixing. In these cases membranes with porous spherulites or spherulites surrounded with a cellular layer were obtained

Temperature induced structural changes in even-odd nylons with long polymethylene segments

Structural transitions of nylons 8 9 and 12 9 heating and cooling processes were investigated using calorimetric, spectroscopic during and real time X-ray diffraction data. These even-odd nylons had three polymorphic forms related to structures where hydrogen bonds were established in two planar directions. Heating processes showed a first structural transition at low temperature where the two strong reflections related to the packing mode of the low temperature structure (form I) disappeared instead of moving together and merging into a single reflection, as observed for conventional even-even nylons. The high temperature structure corresponded to a typical pseudohexagonal packing (form III) attained after the named Brill transition temperature. Structural transitions were not completely reversible since an intermediate structure (form II) became clearly predominant at room temperature in subsequent cooling processes. A single spherulitic morphology with negative birefringence and a flat-on edge-on lamellar disposition was obtained when the two studied polyamides crystallized from the melt state. Kinetic analyses indicated that both nylons crystallized according to a single regime and a thermal nucleation. Results also pointed out a secondary nucleation constant for nylon 12 9 higher than that for nylon 8 9, suggesting greater difficulty in crystallizing when the amide content decreased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2494–2506Peer ReviewedPostprint (author's final draft