Transcrystallized polymer crystals

In addition to the characterization of the morphology formed as a result of different thermal history, the role of interfaces and shear in transcrystallization (Fig. 18) (164,183) and thin films (184), as well the confinement effects of ultrathin films (185,186) on polymer crystallization, have been addressed by SFM approaches. 

Anisotropic friction was observed for all samples discussed in this paper. The anisotropy is directly correlated with the directionality of the polymer molecules at the surface of the specimens. The directionality was either confirmed experimentally by AFM (for uniaxially oriented polymers and the transcrystallized PEO) or reported in the literature in numerous diffraction studies for extended-chain polymer single crystals. The existence of regularly packed folds at the surface of lamellar polymer crystals is still a matter of discussions. 

Presence of TCL changes the properties of crystalline matrix. Transcrystallization of isotactic polypropylene in the presence of different fibers has been thoroughly analyzed. Gray as the first one provided detailed description of isotactic polypropylene behavior in the presence of wood fibers using polarized light microscopy. He observed that when melted polymer is cooled down, it crystallizes in spherulite forms in nonisothermal and isothermal conditions, creating additionally a TCL. 

Fig. 18. SFM image of the a, 8-cylindritic columnar morphology of transcrystallized isotactic PP induced by pulling of a carbon fiber. On the basis of these observations, Vancso and co-workers concluded that the lamellar growth occurs during epitaxial crystallization on bundles of extended isotactic PP chains, which form during shearing of the polymer matrix by fiber pull. Reprinted with permission from Ref 183. Copyright (1997) Steinkopff Verlag.

For polymers, anisotropic friction 10) was observed on lamellar crystals II -13 as well as on extended-chain crystals obtained by friction transfer deposition 14). The anisotropic friction for lamellar crystals was explained by the occurrence of chain-folding oriented preferentially in planes parallel to the corresponding crystal face. For extended-chain crystals friction anisotropy observed parallel and perpendicular to the chain direction was interpreted by the interlocking asperity model. In this paper we give an overview regarding our nanotribological observations on oriented high density polyethylene (HDPE), poly(tetrafluoroethylene) (PTFE) and on crystals of polyethylene (PE) and transcrystallized poly(ethylene oxide) (PEO). 

Moreover, if the fiber is in the crystalline state, as in the case of surface-induced polymer epitaxy, lattice matching between the polymer and fiber crystals provides another favorable situation for transcrystallization. For example, the existence of excellent matching of nylons and iPP with high-modulus graphitic carbon fibers has led to the transcrystallization of nylons and iPP around the carbon fibers [135]. Taking this into account, the case in which both fiber and matrix are of... 

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