result has been verified by the parallel simulations (Zha and Hu 2009 ). The
interface-induced crystal nucleation in the precipitated polymer droplets explains
the special bowl-shape morphology of solution-grown crystallites observed at low
temperatures in a poor solvent. Interface-induced crystal nucleation may be useful
in the fabrication of a well-designed texture of multi-component systems in order to
realize an integration of the advantages in each component.
11.5 Accelerated Crystal Nucleation in the Single-Chain
Systems
When a polymer solution becomes extremely diluted, each polymer chain will be
surrounded only by solvent molecules, which constitutes an isolated single-chain
system. Since a flexible polymer chain contains a large number of monomers, and
each monomer may contain variable chemical structures with multiple interactions
such as hydrogen bonding, hydrophobic and hydrophilic interactions, the phase
transition behaviors of such a small system will be very complicated. A typical
example is the protein folding from a random coil to its native state. Various
interactions between monomers make diverse contributions to the self-assembly
behaviors of proteins. Such a single-chain system is often regarded as the smallest
complex system in the world.
Hsien Wu first proposed that the mechanism for a protein to lose its living
function is the unfolding of its native conformation (Wu 1931 ). Anfinsen pointed
Fig. 11.8 Theoretical melting points (solid lines) versus volume fraction of crystallizable
polymers in polymer solutions with chain length 128 monomers. The mixing interaction
parametersB/Ecare labeled near thecurves, andEp/Ec¼1. Thedashed linesare the theoretical
binodal curves, and thedotted linesare the melting points of the bulk phases in comparison with
those at interfaces with the concentration 0.5 (Zha and Hu 2009 ) (Reprinted with permission)
232 11 Interplay Between Phase Separation and Polymer Crystallization