Nucleation, crystal primary

Equation 20 predicts a free-energy barrier for primary crystal nucleation (i.e., the free-energy difference between the top of the barrier and the initial coil state) as... 

Ellis RJ (1997) Molecular chaperones avoiding the crowd. Curr Biol 7 R531-R533 Flory PJ (1953) Principles of polymer chemistry. Cornell University Press, Ithaca Graham PD, McHugh AJ (1998) Kinetics of thermally induced phase separation in a crystallizable polymer solution. Macromolecules 31 2565-2568 Hu WB, Frenkel D (2005) Oriented primary crystal nucleation in lamellar diblock copolymer systems. Faraday Discuss 128 253-260... 

In a broad sense, the concept of molecular nucleation can be applied to the primary crystal nucleation too, since the sizes of primary nuclei are usually smaller than the coil size of single macromolecules [37]. As a matter of fact, both experiments and simulations have provided evidences for the crystallization within a single homopolymer chain [38-42]. 

The result about the supercooUng dependence is consistent with the above estimation for primary crystal nucleation, implying the feasibility of a molecular-nucleation process in primary crystal nucleation of bulk polymers. Furthermore, this free-energy barrier is independent of chain length, in... 

From the above discussions, one may get the impression that molecular nucleation is quite appropriate to describe the rate-determining step of both primary crystal nucleation and crystal growth. Furthermore, the situation for molecular nucleation can be quite flexible. According to Eq. (3.10), the substrate for secondary molecular nucleation is not necessarily very smooth, because a terrace step crossing over the nuclei will not affect its lateral surface free energy much. Each event of molecular tiiicleation should be activated by a single macromolecule. Some other macromolecules can be involved in the same event of molecular nucleation and may act in a passive way. 

In practice, to get over the nucleation barrier via thermal fluctuations, the initiation of primary crystal nucleation requires a crystallization temperature something lower than 7, and thus a supercooling for crystallization is defined as... 

After primary crystal nucleation, crystals begin to grow. The crystal growth may be diffusion-controlled or interface-controlled. If crystal grows under a large supercooling in dilute polymer solutions, the growth rate is mainly controlled by... 

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