Session J49: Focus Session: Crystallization in Single-, Multicomponent, and Hybrid Systems I

11:15 AM–2:15 PM, Tuesday, February 28, 2012
Room: 162A

Sponsoring Unit: DPOLY
Chair: Christopher Li, Drexel University

Abstract ID: BAPS.2012.MAR.J49.8

Abstract: J49.00008 : Crystallization and Microphase Separation in Chiral Block Copolymers

1:03 PM–1:39 PM

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Author:

  Rong-Ming Ho
    (Department of Chemical Engineering, National Tsing Hua University, Taiwan)

Block copolymers composed of chiral entities, denoted as chiral block copolymers (BCP*s), were designed to fabricate helical architectures from self-assembly. A helical phase (denoted H*) was discovered in the self-assembly of poly(styrene)-$b$-poly(L-lactide) (PS-PLLA) BCPs*. To examine the phase behavior of the PS-PLLA, self-assembled superstructures resulting from the competition between crystallization and microphase separation of the PS-PLLA in solution were examined. A kinetically controlled process by changing non-solvent addition rate was utilized to control the BCP* self-assembly. Single-crystal lozenge lamellae were obtained by the slow self-assembly (i.e., slow non-solvent addition rate) of PS-PLLA whereas amorphous helical ribbon superstructures were obtained from the fast self-assembly (i.e., fast non-solvent addition rate). As a result, the formation of helical architectures from the self-assembly of the PS-PLLA reflects the impact of chirality on microphase separation, but the chiral effect might be overwhelmed by crystallization. Consequently, various crystalline PS-PLLA nanostructures in bulk were obtained by controlling the crystallization temperature of PLLA ($T_{c,PLLA})$ at which crystalline helices and crystalline cylinders occur while $T_{c,PLLA}\over {\smash{\scriptstyle=}\vphantom{_x}}$}} T_{g,PS}$, respectively. Anisotropic arrangement of the PLLA crystallites grown within the microdomains was identified. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While $T_{c,PLLA}\over {\smash{\scriptstyle=}\vphantom{_x}}$}} T_{g,PS}$, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices and to result in crystalline cylinders.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.J49.8