Shish-kebab model

A shish-kebab model for tbe filament morphology was proposed. The electrospinning process was shown to be a means of creating porous thin films with structural gradients and controlled morphology that could enhance biocompatibility. 

Pig. 8.2. Rodlike polymer and shish-kebab model, which consists of N-Lib beads of diameter b placed along a straight line. 

As before, the Brownian motion of the polymer can be studied by dynamic light scattering. If we take the shish-kebab model shown in Fig. 8.2, the dynamical structure factor is given by... 

A crude estimation of W is done easily again by neglecting the hydrodynamic interaction in the shish-kebab model. Under the velocity gradient K, the rod rotates with the angular velocity eiu = X (ir ). Hence the velocity of the n-th bead relative to the fluid is... 

Supramolecular structures formed during the crystallization of the melt under a tensile stress have already been described by Keller and Machin25. These authors have proposed a model for the formation of structures of the shish-kebab type according to which crystallization occurs in two stages in the first stage, the application of tensile stress leads to the extension of the molecules and the formation of a nucleus from ECC and the second stage involves epitaxial growth of folded-chain lamellae. 

FIG. 19.1 Morphological models of some polymeric crystalline structures. (A) Model of a single crystal structure with macromolecules within the crystal (Keller, 1957). (B) Model of part of a spherulite (Van Antwerpen, 1971) A, Amorphous regions C, Crystalline regions lamellae of folded chains. (C). Model of high pressure crystallised polyethylene (Ward, 1985). (E) Model of a shish kebab structure (Pennings et al., 1970). (E) Model of paracrystalline structure of extended chains (aramid fibre). (El) lengthwise section (Northolt, 1984). (E2) cross section (Dobb, 1985). 

The effects of the addition of two or more additives (i.e. talc, montmorillonite, Ceo, PDLA, and various polysaccharides) have been studied by Tsuji et al. [313], while those of talc and/or triphenyl phosphate as a plasticizer were investigated by Xiao et al. [330], Derivative N,N,N-tricyclohexyl-l,3,5-benzenetricarboxylamide was used as a model to tailor the crystalline superstructure of PLLA three crystal morphologies including conelike, shish-kebab, and needlelike structures were obtained by melt crystallization [331],... 

The shish-kebab (cylindrite) stractures can be formed by compression as observed in in the UHMWPE/iPP blends. Two different self-seeding nucleation origins can be proposed (a) the classical row-nuclei model (b) thread-like nuclei. ... 

Semicrystalline materials are often considered as composite materials at a nanoscale and then the use of micromechanical models to predict the macroscopic properties is quite natm al. But semicrystalline materials camiot be put so easily in one of the three classical previous modeled families defined for composites and polycrystalline materials because the crystalline microstructure is complex and organized at several scales. Therefore, the first question is At which scale do we have to consider this composite material At a microscale, that is the scale of the crystalline microstructure (spherulites, shish-kebabs) Or at the nanoscale of the crystalline lamellae ... 

Haudin et al. [21] described shear-induced crystallization, taking into account both spherulites and shish-kebabs. The shish-kebabs were modeled as cylinders with an infinite length. Potential nuclei disappeared by activation and absorption, and new ones were created by flow. The crystallization was described by a set of differential equations, which were solved numerically. 

Electron micrographs, made after dissolving the LMW component, showed an unexpected shish-kebab structure for these special blends adjacent kebabs are interconnected by multiple short shish, quite different from the conventional results/view of one shish connecting multiple kebabs (see Fig. 14.7). It is not clear whether this is a result of the special blend or also applies to normal entangled blends. Nevertheless, based on these results Hsiao et al. [85] proposed a model for the shish-kebab formation not discussed in detail here. 

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