Spherulites formation

Recent developments have allowed atomic force microscopic (AFM) studies to follow the course of spherulite development and the internal lamellar structures as the spherulite evolves [206-209]. The major steps in spherulite formation were followed by AFM for poly(bisphenol) A octane ether [210,211] and more recently, as seen in the example of Figure 12 for a propylene 1-hexene copolymer [212] with 20 mol% comonomer. Accommodation of significant content of 1-hexene in the lattice allows formation and propagation of sheaf-like lamellar structure in this copolymer. The onset of sheave formation is clearly discerned in the micrographs of Figure 12 after crystallization for 10 h. Branching and development of the sheave are shown at later times. The direct observation of sheave and spherulitic formation by AFM supports the major features that have been deduced from transmission electron and optical microscopy. The fibrous internal spherulite structure could be directly observed by AFM. 

Homogeneous melt, Todt < Tc > Tg. In diblock copolymers exhibiting homogeneous melts, microphase separation is driven by crystallization if Tg of the amorphous block is lower than Tc of the crystallizable block. This generally results in a lamellar morphology where crystalline lamellae are sandwiched by the amorphous block layers and spherulite formation can be observed depending on the composition [6-10]. 

Spherulite formation by geometrical selection may rarely be seen on crystals with isotropic Habitus. Native arsenic. As, occurs in a confeito-like form, and is a type of spherulite grown through the geometrical selection of rhombohedral crystals. Spherical aggregation of calcite crystals with nail-head Habitus is also observed. Semi-spherical aggregates of platy barite crystals known as desert rose are shown in Fig. 8.6. 

Jabarin, S. A. and Stein, R. S. Light scattering and microscopic investigations of mesophase transitions of cholesteryl myristate. II. Kinetics of spherulite formation. J. Phys. Chem. 77, 409 (1973)... 

Rupture occurs without important plastic deformation when the ribbons of some neighboring spherulitic formations show a parallel orientation in the contact zone. Conversely, considerable elongation occurs when the orientation is normal at the contact limit because of plastic deformation of the ribbons (Figures 4 through 6). 

Probing spherulite formation both chemically and morphologically - to understand the correlated information. 

Figure 10.10 illustrates the kinetics of spherulite formation with and without fillers. The left half of each photograph shows spherulite growth without a filler. Two attributes of this growth are evident ... 

Tendency to crystallization in fibres with additives HC-2, HC-5, HC-6 increases still more. Radial spherulite formations of rather large size are observed in microphotoes of fibres modified by these hexaazocyclanes (Figure 3.6, 9, 10). 

As mentioned above, PLA should be addressed as a random copolymer rather than as a homopolymer the properties of the former depend on the ratio between L-lactic acid and D-lactic acid units. A few studies describe the influence of the concentration of D-lactic acid co-units in the PLLA macromolecule on the crystallization kinetics [15, 37, 77-79]. The incorporation of D-lactic acid co-units reduces the radial growth rate of spherulites and increases the induction period of spherulite formation, as is typical for random copolymers. In a recent work, the influence of the chain structure on the crystal polymorphism of PL A was detailed [15], with the results summarized in Figure 5.13. It shows the influence of D-lactic acid units on spherulite growth rates and crystal polymorphism of PLA for two selected molar mass ranges. 

The radial growth kinetics of PHB spherulite formation have been evaluated in terms of Hoffman s theoretical relationship ... 

The lamella stacks, which grow during spherulite formation, may break and branch out, new lamella stacks may emerge or grow together with others. The ball-shaped spherulite is filled with such crystalline fragments. 

F. Khoury, Mechanisms of Polymer Spherulite Formation, Private communication. 

Krebs MRH, Bromley EHC, Rogers SS et al (2005) The mechanism of amyloid spherulite formation by bovine insulin. Biophys J 88 2013-2021... 

Domike KR, Donald AM (2007) Thermal dependence of thermally induced protein spherulite formation and growth kinetics of p-lactoglobulin and insulin. Biomacromolecules... 

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