This
study examined crystal orientation confined within a lamellar
microdomain morphology formed by the blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and
polystyrene-block-poly(acrylic acid) (PS-b-PAA) through wide-angle X-ray diffraction. The hydrogen-bonding
interaction between PEO and PAA molecules enabled block copolymers
to co-organize into a microphase-separated morphology without inducing
macrophase separation, but it hampered PEO crystallization. PEO crystallization
that occurred at −20 °C resulted in the nucleation mechanism
to be dominant, thus leading to the formation of small crystals. Small
crystals allowed them to be free from spatial confinement, and they
tended to be oriented with their c-axis parallel
to the microdomain interface. By contrast, when PEO was crystallized
at 40 °C, the high temperature facilitated PEO crystals to exhibit
large crystallite sizes, which aligned perpendicularly to the microdomain
interface. An increase in the PS-b-PAA concentration
considerably reduced the crystallizability of PEO. The presence of
a low amount of crystals and additional lateral confinement formed
by hydrogen-bonded PEO/PAA reduced the degree of orientation regardless
of the crystallization temperature.
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