Polymer crystallization, nucleation regime

Hu W, Cai T (2008) Regime transitions of polymer crystal growth rates molecular simulations and interpretation beyond Lauritzen-Hoffman model. Macromolecules 41(6) 2049-2061 Hu W, Frenkel D (2004) Effect of metastable liquid-liquid demixing on the morphology of nucleated polymer crystals. Macromolecules 37(12) 4336-4338 Hu W, Frenkel D (2005) Polymer crystallization driven by anisotropic interactions. Adv Polym Sci 191 1-35... 

The regime-transition phenomena of polymer crystal growth have been well explained on the basis of the Lauritzen-Hoffman model [14,15]. Nevertheless, the assumptions about the details of secondary crystal nucleation can be replaced by the intramolecular crystal nucleation, without a substantial loss of semi-quantitative predictions about regime transitions. 

The drawing temperature is selected above the Tg in order to modify the amorphous phase in the rubbery state the initial crystallinity, the nucleation and growth rate according to the crystallization regimes I-III, the polymer chain mobility, and the polymer molecular weight are important factors for optimization of fiber orientation and crystallization. Typically, PLLA melt-spun fibers after drawing at 160°C reach a crystallinity of about 50-70% [24, 80]. 

For regime II, large numbers of surface nuclei form on the substrate at a rate I and spread slowly at a velocity g. This results in multiple nucleation acts commencing before previous ones have finished. The newly formed surface is rough and uneven on a molecular scale. Gjj = b(2ig), i.e. polymer crystal growth is proportional to the square root of the surface nucleation rate and A is thus defined ... 

These three cases are the reason for the existence of three regimes of crystallization and the respective changes in polymer morphology. The transitions to different regimes are possible because the completion rate depends on temperature but much less than the nucleation rate. The... 

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