Shear-induced crystallization precursors

Yang L, Somani RH, Sics I, Hsiao BS, Kolb R, Fruitwala H, Ong C. Shear-induced crystallization precursor studies in model polyethylene blends by in-situ rheo-SAXS and rheo-WAXD. Macromolecules 2004 37 4845-4859. 

Azzurri F, Alfonso GC. Lifetime of shear-induced crystal nucleation precursors. Macromolecules 2005 38 1723-1728. 

The epitaxial growth and the formation of a shish-kebab stmcture were also investigated in high molecular weight iPP (HMW-iPP)/low-molecular-weight LLDPE (LMW-LLDPE) blends [21]. The formation of the initial crystallization precursor structure was investigated by using synchrotron WAXS/SAXS techniques at 130 and 140 °C. Shear was applied at temperatures above the cloud points of these blends, and therefore, the HMW-iPP chains could form a flow-induced crystalline stmcture in the blends only at 6 and 9 wt% of HMW-iPP LMW-LLDPE merely served as the amorphous matrix (Fig. 5.3). When the HMW-iPP... 

To understand the mechanism leading to enhancement of crystallization under shear, the structure of the so-call shish or row nuclei, the primary nucleus induced by flow, is essential. The common textbook picture is that the shish consist of extended-chain crystals that maybe defective [184-189]. It is generally accepted that structures with some degree of order are induced by the flow before the onset of crystallization, which can be long living at shallow supercooling [127-150]. These shear-induced precursors have been described... 

The self-organizing nature of liquid crystal polymers is reflected in their complex flow behavior. The relaxation phenomenon of lyotropic polymer solution after shear cessation leads to band texture morphology that can be further induced to isotropic materials. Future research should focus on solvents influence on band size implicitly related to the induced pattern in polymers with different structures. Another aspect that could be explored is the imidization of patterned polyimide precursors and those conditions in which the texture is still maintained. 

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