Spherulite positive

At very small strains within the viscoelastic region (e<0.5%), deformation within the PP solid is confined to disordered amorphous regions [97,98) due to their inherently low stiffness at temperatures above their Tg (-10 °C). In this deformation region, spherulites undergo affine deformation on the whole. Inside the spherulites, rotation of lamellae occurs [101]. The resulting orientation of lamellae depends on their position within the spherulite in respect to the orientation of the external deformation [102-104],... 

Much effort has been devoted to investigating the detailed architectures and the construction of spherulites. Early investigations of the crystallization of polymers through optical microscopy (OM) [7,8] posited that polymer spherulites consisted of radiating fibrous crystals with dense branches to fill space. Later, when electron microscopy (EM) became available, spherulites were shown to be comprised of layer-like crystallites [9,10], which were named lamellae. The lamellae are separated by disordered materials. In the center of the spherulites, the lamellae are stacked almost in parallel [5,6,11-15]. Away from the center, the stacked lamellae splay apart and branch, forming a sheaf-like structure [11,13-15]. It was also found that the thicknesses of lamellae are different [5,6,11,12]. The thicker ones are believed to be dominant lamellae while the thinner ones are subsidiary lamellae. 

Fig. 36 Phase image shows the structure of the eyes at the center position of a spherulite of BA-C8 [62]...

Fig. 15.6 Raman spectra recorded along the diameter of an iPP spherulite during isothermal crystallization from the melt at Tj, = 130°C. The variation in Raman bands at 809 cm and 841 cm indicating the amorphous and crystalline content of iPP are matched -with their positions on the polymer (Reprinted from [38])...

Fig. 2 Visible light micrograph of spherulites from a crystalline diepoxide taken with a 5X lens and cross polarization. The observed maltese cross pattern arises from the spiral positioning of lamella along the radial growth direction. The high refractive index c-axis is tangential to the spherulite s radius.

In injection molded composites of polypropylene containing short glass fibers, the fiber orientation depended on the flow pattern (which, in turn, is related to mold thickness, the position of the gate, and flow rate)." Substantial variation was detected along the thickness of the sample. Crystallites followed a pattern of fiber distribution but they grew in a direction perpendicular to the direction of the fiber and specimen surface. The direction of spherulite growth was different in neat resin where crystallites grew parallel to the surface of the mold (specimen). 

Optical microscopy using polarized light gives a first hint on the crystallinity of the obtained structures. A typical result of optical micrographs obtained without polarization, parallel and perpendicular orientation of the polarizer and analyzer are shown in the Fig. 4. If the relative position of the polarizer and analyser is changed the different regions of the spherulites change their colour, while the... 

Fig. 5. Details of a Rubrene spherulite. (a) Center, (b) Iris, (c) spherulite rim, and (d) surrounding amorphous matrix. Z-scale (a) 300 nm, (b) 50 nm, (c) 30 nm and (d) 5 nm. The insets show the cantilever position relative to the spherulite center.

Spherulites are classified as positive when the refractive index of the polymCT chain is greater across the chain than along the axis, and negative whrai the greater refractive index is in the axial direction. They also show various other features sueh as zigzag patterns, concentric rings, and dendritic strucfirres. 

Fig. 5.16 (a) A schematic diagram of the observed light scattering from a spherulitic polymer film placed between crossed polarisers. The straight lines indicate the directions of polarisation and the closed curves indicate one contour of intensity for each of the four patches of light seen. The crosses indicate the positions of maximum intensity, (b) A photograph of the corresponding pattern for a polyethylene film, ((b) Reproduced by permission of the American Institute of Physics.)... 

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