homogeneous crystal nucleation inducing random stacking of lamellar crystals. If
microphase separation occurs first, we observe crystallization confined in
microdomains. The microdomains not only provide a spatial template for crystal-
line ordering, but also guide crystal orientations (Hu and Frenkel 2005 ). Fig-
ure11.12a, bdemonstrate that the lamellar microdomains can induce parallel
stacking of lamellar crystals at high crystallization temperatures, while the homo-
geneous primary nucleation generates only random stacking of lamellar crystals
(Ma et al. 2011 ). Parallel stacking of lamellar crystals benefits the barrier properties
of semi-crystalline engineering plastics, applied in wrapping films, Coke bottles
and oil tanks (Lemstra 2009 ). Such a template-controlled growth actually widely
exists in the bio-mineralization process, such as the bio-fabrication of shells,
enamels and bones in Nature (Currey 2005 ).
11.7 Implication of Interplay in Biological Systems
There are wide implications of phase-transition interplay in the biological systems,
besides protein folding and bio-mineralization. Double-helix DNA constitutes a
single rigid chain and has to fold up in order to be stored into the cell nucleus. Since
the persistence length of DNA is as long as 50 nm, the local chain rigidity makes
DNA molecules to fold up into a toroid ring similar to a “doughnut”, with the help
of certain enzymes. As a result of interplay between chain extending and parallel
stacking, the folding speed follows a nucleation-controlled kinetics (Yoshikawa
and Matsuzawa 1996 ). The parallel packing interactions of DNA chains mainly
originate from the concentration fluctuations of counter-ions surrounding the poly-
electrolyte chains, as introduced in Sect.4.3.
Fig. 11.12 Snapshots of diblock copolymers obtained after isothermal crystallization under the
conditions of (a)B/Ec¼0.2,T¼4.1Ec/k for prior microphase separation to crystallization; (b)B/
Ec¼0.2,T¼2.9Ec/k for crystallization first, withEp/Ec¼1 for the crystallizable yellow 16-
mer blocks, and 0 for the noncrystalliableblue16-mer blocks. All the bonds are drawn as cylinders
in the cubic lattice of 64^3 with periodic boundary conditions (Ma et al. 2011 ) (Reprinted with
permission)
236 11 Interplay Between Phase Separation and Polymer Crystallization