calculated from (11.1) and illustrated in Fig.11.7. Supposing polymer blends homo-
geneous although thermodynamically immiscible, the melting point of the crystalliz-
able component will increase with dilution, in contrast to the depression in
thermodynamically miscible blends. Since surface polymers are forced to contact
to the other component, their concentration is relatively lower than that of bulk
polymers. According to Fig.11.7, their melting point appears higher than that of
bulk polymers. This result implies that crystal nucleation at interfaces will be
accelerated with a larger degree of supercooling than that in the bulk phase. Parallel
simulations have verified this interface effect, and such a thermodynamic effect does
not provide any orientation preference to crystal nuclei at interfaces (Ma et al. 2008 ).
In immiscible polymer solutions, the theoretical melting points behave differ-
ently from those in the immiscible blends above. In a poor solvent, the melting
point does not move monotonically upward upon dilution, but rather first downward
then upward due to the significant effect of mixing entropy, as demonstrated in
Fig.11.8. This result suggests that, only in a sufficiently poor solvent, can polymer
crystal nucleation be accelerated at interfaces (Zha and Hu 2009 ). For instance at
T¼4.5EC/k, when the mixing energy parameter is 0.3, polymer melting point at
the interface (determined by the melting point curve at the supposed polymer
concentration 0.5) is lower than that in the bulk phase (determined by the melting
point curve at the concentration crossing the binodal curve atT¼4.5EC/k)in
Fig.11.8. When the mixing energy parameter becomes 0.4, the melting point at
interfaces is higher than that of the bulk phase. Therefore, the interfaces can induce
crystal nucleation only in a sufficiently poor solvent of polymer solutions. This
Fig. 11.7 Theoretical melting points versus volume fractions of crystallizable polymers in
homogeneous symmetric polymer blends with chain length 16 monomers, showing melting
point risen-up on dilution under the immiscible thermodynamic conditions. The mixing interaction
parametersB/Ecare labeled near thecurves, andEp/Ec¼1. Thearrowis drawn to guide the eyes
(Ma et al. 2008 ) (Reprinted with permission)
11.4 Accelerated Crystal Nucleation at Liquid Interfaces 231